Any one who has in slab radiant particularly anyone using a propane or ng tankless water heater experimented with different slab inlet temps vs fuel consumption. I have a 2400 sqft building using a nortiz tankless and it's doing great I've just been playing with things to find where it's happiest. Building is heated full time at a single temp setting. The people i bought Everything from recommended starting with 120 they said it gave the best results between response and economy. I bumped it down to 110 and it didn't seem to have much effect but i don't yet have anything in place to monitor run time and fuel consumption besides looking at the tank gauge daily. Thanks attached is a pic of my install
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Radiant tunning
- Thread starter Jking24
- Start date
The water temp required is based on outside temp and the insulation ..... the goal with any system is to match the load to the buildings need.
As temps drop you will need hotter water ...
That's why people set radiant up with outdoor reset (ODR).
What you are doing is heating the slab and waiting for the heated slab to heat the building ... it is guess work. Again -- the goal is lowest temp water to heat the building
I see two pumps ... but no close spaced "T" ... how are you doing separation?
Where are you measuring the temp -- boiler ? or temp to floor. these are different
As temps drop you will need hotter water ...
That's why people set radiant up with outdoor reset (ODR).
What you are doing is heating the slab and waiting for the heated slab to heat the building ... it is guess work. Again -- the goal is lowest temp water to heat the building
I see two pumps ... but no close spaced "T" ... how are you doing separation?
Where are you measuring the temp -- boiler ? or temp to floor. these are different
mobetta
Well-known member
I'm tring to figure out if theres a "close boiler loop"
maybe another pic that gets the whole piping in the shot???
one benifit of using a boiler vs water heater is most mod cons come with an ODR so they modulate output according to exterior temperatures.
not sure how to do that on a water heater
seems like most water heaters are too many btus to be efficient for a small shop
maybe another pic that gets the whole piping in the shot???
one benifit of using a boiler vs water heater is most mod cons come with an ODR so they modulate output according to exterior temperatures.
not sure how to do that on a water heater
seems like most water heaters are too many btus to be efficient for a small shop
Randy in Maine
Well-known member
I never care what the outside temp is. I just keep the shop thermostat set to 52º. My thermostat is mounted on an interior wall about 4' above the floor. The thermostat either calls for heat or it doesn't.
I'm tring to figure out if theres a "close boiler loop"
maybe another pic that gets the whole piping in the shot???
one benifit of using a boiler vs water heater is most mod cons come with an ODR so they modulate output according to exterior temperatures.
not sure how to do that on a water heater
seems like most water heaters are too many btus to be efficient for a small shop
The best way when using an on-demand water heater -- create a buffer tank. The water heater has the tank to heat and you pull from the tank -- it's like a big loss header.
What many do is try and set the output of the water heater low -- but now you have a small delta and the heater may or may not be able to modulate that low .. most can not.
The inefficiencies are not noticed with natural gas as the fuel is so cheap and the supply endless. with propane being 4x the cost and the tank going down -- it's more noticeable .. especially as you increase building size and colder area
It's a closed loop system the heater has variable output 17000btu -199000btu their is no mixing valve so measured temp out of the heater is slab inlet temp +- whatever minimal losses their are from tank to slab roughly 8' of pipe the thermostat measures ambient inside the building and controls the pumps the water heater kicks in when it senses water flow. Water temp is set independently and the floor system has no control of it.The system is performing beautifully for a lack of better words I'm just playing with output temp to see if their are any fuel savings to be had their.
At some point the slab gets warm -- the return temp of the water nears the required output and the delta drops ... what does the heater do?
Much depends on the building size and insulation .....
My new house has 5000sf of space heated with radiant -- the boiler is under 70k with modulation down to 17k.
You just have to play with your system ... some people eventually use a slab sensor to maintain a minimum slab temp ... You have to be the ODR
Much depends on the building size and insulation .....
My new house has 5000sf of space heated with radiant -- the boiler is under 70k with modulation down to 17k.
You just have to play with your system ... some people eventually use a slab sensor to maintain a minimum slab temp ... You have to be the ODR
At some point the slab gets warm -- the return temp of the water nears the required output and the delta drops ... what does the heater do?
Much depends on the building size and insulation .....
My new house has 5000sf of space heated with radiant -- the boiler is under 70k with modulation down to 17k.
You just have to play with your system ... some people eventually use a slab sensor to maintain a minimum slab temp ... You have to be the ODR
Other than on fire up for about 10-15 seconds the outlet temp of the heater stays pretty much spot on whatever it's set at. It's currently set on 110 and at the temp probe location about 3-4 foot from heater outlet it will read 108.5 to 109 the entire cycle i haven't tried any cooler yet but at 120 setting it would hoover at 119. I ordered a hour meter that i will attach to the system and log but with the heater being variable btu is not necessarily going to reflect actual fuel usage
You don't really have variable output ... unless you have windows open that 2400sf will never need the lowest output of the unit ... 170k . It's always oversized.
I have no idea how it starts out -- some water heaters go on high at start and then drop down. But, again ... the building will never need 170k.
So what temp does it need ? Only you can determine that with trial and error ... when its 5 degrees out it will need more BTU's to keep it warm vs when it's 40 out.
But -- the unit has no idea what the temp outside is. It's just going to pump out what you plug in.
As I said .... the goal is to give the slab just what it needs to keep the building warm. My setup works with a small energy efficient pump that will keep the water moving all the time -- the boiler adjusting the water temp as required based on outside temp.
The other day when it was 28 out the boiler was making 109 to the low loss header ...
Slab temp will determine room temp ..... if you pump in too hot the slab will over shoot or it will radiant unevenly with the space around the tubes warm and the spaces cold
I have no idea how it starts out -- some water heaters go on high at start and then drop down. But, again ... the building will never need 170k.
So what temp does it need ? Only you can determine that with trial and error ... when its 5 degrees out it will need more BTU's to keep it warm vs when it's 40 out.
But -- the unit has no idea what the temp outside is. It's just going to pump out what you plug in.
As I said .... the goal is to give the slab just what it needs to keep the building warm. My setup works with a small energy efficient pump that will keep the water moving all the time -- the boiler adjusting the water temp as required based on outside temp.
The other day when it was 28 out the boiler was making 109 to the low loss header ...
Slab temp will determine room temp ..... if you pump in too hot the slab will over shoot or it will radiant unevenly with the space around the tubes warm and the spaces cold
Thankyou for the info and i understand all the concepts. I was only referencing temps to answer your first question. the heater was sized by the company who designed the system and appears to be able to throttle down enough to not over heat as the delta closes during a cycle. The system also has a slab sensor and is set to maintain a minimum slab temp. As you stated i just need to play with the system to see what it likes best. Im not looking for debates about why a boiler is or isn't better. I asked if anyone had any first hand experience with a similar setup and water heater settings. For a full house setup sutch as yours I'm sure a constant flow system with a high efficiency condensing boiler would probably be the best solution. Unfortunately the cost of those just were not in my budget. As i stated my system is performing very well as installed. It has more than enough capacity to keep up on it coldest days and so far does not seem to struggle on the lower demand days. My building is 2400sqf but also has 15ft ceilings so its a fairly large space to keep at tempYou don't really have variable output ... unless you have windows open that 2400sf will never need the lowest output of the unit ... 170k . It's always oversized.
I have no idea how it starts out -- some water heaters go on high at start and then drop down. But, again ... the building will never need 170k.
So what temp does it need ? Only you can determine that with trial and error ... when its 5 degrees out it will need more BTU's to keep it warm vs when it's 40 out.
But -- the unit has no idea what the temp outside is. It's just going to pump out what you plug in.
As I said .... the goal is to give the slab just what it needs to keep the building warm. My setup works with a small energy efficient pump that will keep the water moving all the time -- the boiler adjusting the water temp as required based on outside temp.
The other day when it was 28 out the boiler was making 109 to the low loss header ...
Slab temp will determine room temp ..... if you pump in too hot the slab will over shoot or it will radiant unevenly with the space around the tubes warm and the spaces cold
Thankyou for the info and i understand all the concepts. I was only referencing temps to answer your first question. the heater was sized by the company who designed the system and appears to be able to throttle down enough to not over heat as the delta closes during a cycle. The system also has a slab sensor and is set to maintain a minimum slab temp. As you stated i just need to play with the system to see what it likes best. Im not looking for debates about why a boiler is or isn't better. I asked if anyone had any first hand experience with a similar setup and water heater settings. For a full house setup sutch as yours I'm sure a constant flow system with a high efficiency condensing boiler would probably be the best solution. Unfortunately the cost of those just were not in my budget. As i stated my system is performing very well as installed. It has more than enough capacity to keep up on it coldest days and so far does not seem to struggle on the lower demand days. My building is 2400sqf but also has 15ft ceilings so its a fairly large space to keep at temp
The ceiling height should not matter -- in fact that's one of the benefits of radiant. With the proper slab temp you don't end up with superheated ceiling and stack effect losses. The slab releases heat and the air cools as you go up .... with radiant the air temp should be lower at the ceiling .... that's why you don't use fans with proper radiant setups.
I was trying to answer your original question -- water temps.
A slab is nothing more than a big radiator. They told you 120 ... because at a constant 120 with the size input you have it's impossible for it not to heat the space. They want the space to heat .... Since this is a new setup == I'm assuming it's reasonably tight and insulated.
The slab sensor is indeed the better way to go as it will cut the system off sooner than a room sensor .. this will help with possible over shooting.
When you do a load it's typically based on a max slab output of 85 degrees -- you can go higher as it's concrete. But that's typically the upper limit as far as comfort.
So what do you have the slab sensor set to ?.... if you have the sensor in the middle of the tubing and it's at 80. Pumping 120 degree water will heat the slab faster than 110 degree water and trip the sensor. It now becomes a factor of how thick the slab and how far apart the tubing -- the slab will continue to release heat. 8" separation will heat faster vs 12"
Ideally you still want the same thing as anyone else --- long run times with the lowest temp water.
With the type system you have my guess is you will want to run colder water dropping it down until the system falls behind ... note the temp and wind conditions. This will show you the low set point at a given outdoor temp. You will quickly discover what temp water is required at various outside temps.
Then it's a simple understanding --- it's been 40 degrees for three weeks .. But, I see it's going to drop into the teens in a few days .... you raise the water temp to one of the historical numbers you have for that outside temp.
The overall savings may or may not be great -- that will depend on the building insulation. Lower water temps always save .... no one can tell you how much.
Thanks the slab sensor is surface mounted with insulation glued over it. It's relatively close to the manifold roughly 3' away. It's currently configured to use the air temp as is primary and the floor only for min and max values. Max is set at 83 and min is 69. I guess because of the close proximity to the manifold coupled with our bi-polar weather around here i have seen quite a swing in slab temp. Anywhere from 70-81 with a thermostat setting of 63. Now it needs mentioning it was 24 degrees Saturday night and it's 52 today so not exactly consistent loads I'm dealing with. My current plan is to run for a week and document fuel consumption compared to average daily temp and then adjust and run another week.The ceiling height should not matter -- in fact that's one of the benefits of radiant. With the proper slab temp you don't end up with superheated ceiling and stack effect losses. The slab releases heat and the air cools as you go up .... with radiant the air temp should be lower at the ceiling .... that's why you don't use fans with proper radiant setups.
I was trying to answer your original question -- water temps.
A slab is nothing more than a big radiator. They told you 120 ... because at a constant 120 with the size input you have it's impossible for it not to heat the space. They want the space to heat .... Since this is a new setup == I'm assuming it's reasonably tight and insulated.
The slab sensor is indeed the better way to go as it will cut the system off sooner than a room sensor .. this will help with possible over shooting.
When you do a load it's typically based on a max slab output of 85 degrees -- you can go higher as it's concrete. But that's typically the upper limit as far as comfort.
So what do you have the slab sensor set to ?.... if you have the sensor in the middle of the tubing and it's at 80. Pumping 120 degree water will heat the slab faster than 110 degree water and trip the sensor. It now becomes a factor of how thick the slab and how far apart the tubing -- the slab will continue to release heat. 8" separation will heat faster vs 12"
Ideally you still want the same thing as anyone else --- long run times with the lowest temp water.
With the type system you have my guess is you will want to run colder water dropping it down until the system falls behind ... note the temp and wind conditions. This will show you the low set point at a given outdoor temp. You will quickly discover what temp water is required at various outside temps.
Then it's a simple understanding --- it's been 40 degrees for three weeks .. But, I see it's going to drop into the teens in a few days .... you raise the water temp to one of the historical numbers you have for that outside temp.
The overall savings may or may not be great -- that will depend on the building insulation. Lower water temps always save .... no one can tell you how much.
Slab sensor placement is always a bit of a guess ..... In my new build I have walls crossing the slab ... so I drilled a hole in the stud equal distant between two tubes and dropped it in. Have also used a length of PEX back to a box or even gray conduit -- both of those being buried in the slab. The stud wall I have found works well.
The goal being to get a relative number -- not too close to a tube that it heats too quick. It's still a relative number and over time you can figure out how the sensor spot relates to other places in the slab. IE: I need a slab temp of "X" where I have the sensor to get "Y" temp at position "Z" on the slab.
There are just too many variables to give definitive answers. Heat load on the building -- number of feet of PEX in the slab ... BTU of the heat source. Unless you had identical buildings and did one thing different in each there is no way to say ... this change makes "X" difference. A building with a lot of solar gain and thick slab often must have a slab sensor ... a room thermostat will turn the slab off and allow it to cool in the afternoon as the sun heats the space and then it will not be able to recover fast enough as the sun goes down. You must maintain a minimum slab temp even risking overheating if you want the space warm. And the reverse as well .... turning off the slab knowing the room will overheat in the sun.
There are basic truths. More PEX = faster response = lower water temp = lower cost. The cost to make the hot water is dependent on source.
Even using a boiler with outdoor reset requires set up time. I have been playing with mine for a couple weeks now. There are two slopes ... the general slope that makes hotter water as outside temps drop and the shift the takes into account the building envelope. As outdoor temps drop a building will lose more BTU based on its construction and placement. Only the very best buildings will have no shift. I have never built one.
The reason slab radiant works so well is the slab is such a large radiator -- the slope for slab is much flatter vs other type radiation and typically has a lower slope shift You can heat a building with 120 water and copper baseboard is often figured out at 180 or even 200 degrees.
I'm only discussing this as you seem as if you are more interested.
Having done many projects -- all with some type of radiant I'm interested myself when the systems are finally running to see if I am correct ...and they work as I had planned.
Even with ODR most systems have a master room control -- for fine adjustment. I have done very complex systems ... but, also simple systems where I have thought them through ..laying out the radiant very carefully with lots of calculations.
My new system with 5ksf only has one system pump -- feeding 4 manifolds and 3 types of radiant using one water temp. I'm running into the same problem as you ..... 25 one day and 55 two days later.
The goal being to get a relative number -- not too close to a tube that it heats too quick. It's still a relative number and over time you can figure out how the sensor spot relates to other places in the slab. IE: I need a slab temp of "X" where I have the sensor to get "Y" temp at position "Z" on the slab.
There are just too many variables to give definitive answers. Heat load on the building -- number of feet of PEX in the slab ... BTU of the heat source. Unless you had identical buildings and did one thing different in each there is no way to say ... this change makes "X" difference. A building with a lot of solar gain and thick slab often must have a slab sensor ... a room thermostat will turn the slab off and allow it to cool in the afternoon as the sun heats the space and then it will not be able to recover fast enough as the sun goes down. You must maintain a minimum slab temp even risking overheating if you want the space warm. And the reverse as well .... turning off the slab knowing the room will overheat in the sun.
There are basic truths. More PEX = faster response = lower water temp = lower cost. The cost to make the hot water is dependent on source.
Even using a boiler with outdoor reset requires set up time. I have been playing with mine for a couple weeks now. There are two slopes ... the general slope that makes hotter water as outside temps drop and the shift the takes into account the building envelope. As outdoor temps drop a building will lose more BTU based on its construction and placement. Only the very best buildings will have no shift. I have never built one.
The reason slab radiant works so well is the slab is such a large radiator -- the slope for slab is much flatter vs other type radiation and typically has a lower slope shift You can heat a building with 120 water and copper baseboard is often figured out at 180 or even 200 degrees.
I'm only discussing this as you seem as if you are more interested.
Having done many projects -- all with some type of radiant I'm interested myself when the systems are finally running to see if I am correct ...and they work as I had planned.
Even with ODR most systems have a master room control -- for fine adjustment. I have done very complex systems ... but, also simple systems where I have thought them through ..laying out the radiant very carefully with lots of calculations.
My new system with 5ksf only has one system pump -- feeding 4 manifolds and 3 types of radiant using one water temp. I'm running into the same problem as you ..... 25 one day and 55 two days later.
Slab sensor placement is always a bit of a guess ..... In my new build I have walls crossing the slab ... so I drilled a hole in the stud equal distant between two tubes and dropped it in. Have also used a length of PEX back to a box or even gray conduit -- both of those being buried in the slab. The stud wall I have found works well.
The goal being to get a relative number -- not too close to a tube that it heats too quick. It's still a relative number and over time you can figure out how the sensor spot relates to other places in the slab. IE: I need a slab temp of "X" where I have the sensor to get "Y" temp at position "Z" on the slab.
There are just too many variables to give definitive answers. Heat load on the building -- number of feet of PEX in the slab ... BTU of the heat source. Unless you had identical buildings and did one thing different in each there is no way to say ... this change makes "X" difference. A building with a lot of solar gain and thick slab often must have a slab sensor ... a room thermostat will turn the slab off and allow it to cool in the afternoon as the sun heats the space and then it will not be able to recover fast enough as the sun goes down. You must maintain a minimum slab temp even risking overheating if you want the space warm. And the reverse as well .... turning off the slab knowing the room will overheat in the sun.
There are basic truths. More PEX = faster response = lower water temp = lower cost. The cost to make the hot water is dependent on source.
Even using a boiler with outdoor reset requires set up time. I have been playing with mine for a couple weeks now. There are two slopes ... the general slope that makes hotter water as outside temps drop and the shift the takes into account the building envelope. As outdoor temps drop a building will lose more BTU based on its construction and placement. Only the very best buildings will have no shift. I have never built one.
The reason slab radiant works so well is the slab is such a large radiator -- the slope for slab is much flatter vs other type radiation and typically has a lower slope shift You can heat a building with 120 water and copper baseboard is often figured out at 180 or even 200 degrees.
I'm only discussing this as you seem as if you are more interested.
Having done many projects -- all with some type of radiant I'm interested myself when the systems are finally running to see if I am correct ...and they work as I had planned.
Even with ODR most systems have a master room control -- for fine adjustment. I have done very complex systems ... but, also simple systems where I have thought them through ..laying out the radiant very carefully with lots of calculations.
My new system with 5ksf only has one system pump -- feeding 4 manifolds and 3 types of radiant using one water temp. I'm running into the same problem as you ..... 25 one day and 55 two days later.
All information is greatly appreciated. I have a infrared camera aswell as a cad file with shots on all the tubing locations pre pour. I'll have to check my sensor location. With the simplicity of my system and it being in a garage as long as it maintains temp consistently its more than comfortable enough. My only real tunning is all towards reducing fuel consumption. I do have three speed pumps that are currently on high. The big question that only time can answer for me is weather lower temps with longer run times or higher temps and shorter run times will yeild less fuel burn. I can already tell that the lower temps are creating a more consistent temp reading as compared to the higher temps created a temp surge then slow fall back to thermostat setting.
meathooker
Well-known member
Yeldogt- I may have to pick your brain on my system as you seem very savvy on Hydronics. A suppler had a sweet 300k btu boiler with 5:1 turn down I’m trying to figure out the best way to utilize it.
He said it turns down to 17k btu ... not 170k
You don't really have variable output ... unless you have windows open that 2400sf will never need the lowest output of the unit ... 170k . It's always oversized.
I have no idea how it starts out -- some water heaters go on high at start and then drop down. But, again ... the building will never need 170k.
He said it turns down to 17k btu ... not 170k
Yeldogt- I may have to pick your brain on my system as you seem very savvy on Hydronics. A suppler had a sweet 300k btu boiler with 5:1 turn down I’m trying to figure out the best way to utilize it.
He said it turns down to 17k btu ... not 170k
Post #6 says 170k EDIT ... you are correct ..sorry.
300k is a huge boiler -- even with turn down at 20%. That's 60k out of the gate.
When you do a heat load on a building --- this is worst case. And it often uses historical low temps that may not occur but a few times a decade. In the old days with few boiler sizes .... installers had to go even larger. So buildings ended up with huge boilers --- these numbers stick and people say ..... that building had a 150k boiler and my space is bigger ... I need more.
Same thing happens with AC. When I do a load test I watch the upper limits of both the outside and the inside target. Most are extreme and will give you too big on both ends.
The issue with combination boilers w/ radiant .... the size to heat the water has to be so high that it often throws the boiler in the oversized camp. A straight on-demand has the additional problem of needing more head on the pump.
The OP has a larger space and this is helping him vs the same heater in a two car garage.
heating water as it goes through a heat exchanger takes a lot of BTU's -- you only get one pass. A typical 40 gallon tank water heater is only about 26k BTU .... and that's input not net to the tank.
Manufacturers are now coming out with small boilers directly linked to small water tanks -- 25g tanks that the boiler can quickly reheat.
All information is greatly appreciated. I have a infrared camera aswell as a cad file with shots on all the tubing locations pre pour. I'll have to check my sensor location. With the simplicity of my system and it being in a garage as long as it maintains temp consistently its more than comfortable enough. My only real tunning is all towards reducing fuel consumption. I do have three speed pumps that are currently on high. The big question that only time can answer for me is weather lower temps with longer run times or higher temps and shorter run times will yeild less fuel burn. I can already tell that the lower temps are creating a more consistent temp reading as compared to the higher temps created a temp surge then slow fall back to thermostat setting.
Thinking a bit more on your system ....my guess is with the Alpha 2 pump that will work with a delta T ... you could have used one of those pumps and it would have run your system based on return temp from the slab .. constant circulation using almost not power. I have the slightly less expensive Alpha 2 on my system they have an auto and pressure/ flow settings. The boiler loop typically is using 15watts and the other about 40w .
The cool thing about the new pumps is they can make complex system -- less complex. My new system has zine controls on three manifolds and the 4th has a zone valve to control the whole manifold. The Alpha pump understand when things open and close and it automatically adjusts the flow. Not many years ago ... each manifold would have needed a pump and controls ...possible bypass loops
I was wondering where the 170k number was coming from.Post #6 says 170k EDIT ... you are correct ..sorry.
300k is a huge boiler -- even with turn down at 20%. That's 60k out of the gate.
When you do a heat load on a building --- this is worst case. And it often uses historical low temps that may not occur but a few times a decade. In the old days with few boiler sizes .... installers had to go even larger. So buildings ended up with huge boilers --- these numbers stick and people say ..... that building had a 150k boiler and my space is bigger ... I need more.
Same thing happens with AC. When I do a load test I watch the upper limits of both the outside and the inside target. Most are extreme and will give you too big on both ends.
The issue with combination boilers w/ radiant .... the size to heat the water has to be so high that it often throws the boiler in the oversized camp. A straight on-demand has the additional problem of needing more head on the pump.
The OP has a larger space and this is helping him vs the same heater in a two car garage.
heating water as it goes through a heat exchanger takes a lot of BTU's -- you only get one pass. A typical 40 gallon tank water heater is only about 26k BTU .... and that's input not net to the tank.
Manufacturers are now coming out with small boilers directly linked to small water tanks -- 25g tanks that the boiler can quickly reheat.
Thinking a bit more on your system ....my guess is with the Alpha 2 pump that will work with a delta T ... you could have used one of those pumps and it would have run your system based on return temp from the slab .. constant circulation using almost not power. I have the slightly less expensive Alpha 2 on my system they have an auto and pressure/ flow settings. The boiler loop typically is using 15watts and the other about 40w .
The cool thing about the new pumps is they can make complex system -- less complex. My new system has zine controls on three manifolds and the 4th has a zone valve to control the whole manifold. The Alpha pump understand when things open and close and it automatically adjusts the flow. Not many years ago ... each manifold would have needed a pump and controls ...possible bypass loops
The only thing about that that would be a problem for my current configuration is the tankless setup it essentially operates independently and is triggered internally based on flow. Im not aware of this being adjustable or externally controllable with the particular unit i have.
Denwood
Well-known member
Any one who has in slab radiant particularly anyone using a propane or ng tankless water heater experimented with different slab inlet temps vs fuel consumption. I have a 2400 sqft building using a nortiz tankless and it's doing great I've just been playing with things to find where it's happiest. Building is heated full time at a single temp setting. The people i bought Everything from recommended starting with 120 they said it gave the best results between response and economy. I bumped it down to 110 and it didn't seem to have much effect but i don't yet have anything in place to monitor run time and fuel consumption besides looking at the tank gauge daily. Thanks attached is a pic of my install
110 is likely fine. I ran our system (about 4600 sq/ft) at that temp with four zones. The triangle tube tankless unit modulates to whatever the load is, as likely does yours. As you're running a single temp, I don't think you'll see any change in overall use (assuming that your unit modulates output) between 110 or 120.
You basically have separation ... you don't seem to be using close spaced "T's" ... but, it must be working ...
The system pump to the slab ... can be smart and work off of a delta.
The boiler/ water heater just keeps i's loop at whatever you pick -- the smart pump pulls what it needs.
The boiler pump just needs to be pumping enough to satisfy the boiler/water heater flow requirements .... You can play around with less flow
The system pump to the slab ... can be smart and work off of a delta.
The boiler/ water heater just keeps i's loop at whatever you pick -- the smart pump pulls what it needs.
The boiler pump just needs to be pumping enough to satisfy the boiler/water heater flow requirements .... You can play around with less flow
The unit is adjustable in 5 degree increments from somthing like 85-140110 is likely fine. I ran our system (about 4600 sq/ft) at that temp with four zones. The triangle tube tankless unit modulates to whatever the load is, as likely does yours. As you're running a single temp, I don't think you'll see any change in overall use (assuming that your unit modulates output) between 110 or 120.
I understand what your saying I'm not sure what my heater does when flow is still present but delta is low or non. My guess is since it's designed to be a residential water heater and that scenario virtualy non existent that is not equipped to deal with it. My system is currently setup a a single zone and no mixing valve. I do have manual valves on each of the 6 300' loops but have not really found any uneven areas or signs that a particular loop needs any more or less flowYou basically have separation ... you don't seem to be using close spaced "T's" ... but, it must be working ...
The system pump to the slab ... can be smart and work off of a delta.
The boiler/ water heater just keeps i's loop at whatever you pick -- the smart pump pulls what it needs.
The boiler pump just needs to be pumping enough to satisfy the boiler/water heater flow requirements .... You can play around with less flow
You don't have a picture of all the piping -- but you mention two pumps. I'm assuming there is a pump for the heater and one for the system?
... Most on-demand water heaters don't modulate down as low as yours -- so that helps a lot.
... Most on-demand water heaters don't modulate down as low as yours -- so that helps a lot.
You don't have a picture of all the piping -- but you mention two pumps. I'm assuming there is a pump for the heater and one for the system?
... Most on-demand water heaters don't modulate down as low as yours -- so that helps a lot.
Their are two pumps in the picture one is in the corner and the other is only half shown but the sytem is set up as basically one primary loop with a pump on each side the valve that runs vertically and is closed is a bypass valve and i beleive that is where a mixing valve would be in a more typical setup with a tank. I also played with the sytem a little last night and found my heater will shut down when the delta closes and flow is still present. It seems to be more of a safety feature and not ment to be used for normal modulation. It allowed it to over temp 5 degrees before shutting down then refired at 1-2 degrees below the set point
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Their are two pumps in the picture one is in the corner and the other is only half shown but the sytem is set up as basically one primary loop with a pump on each side the valve that runs vertically and is closed is a bypass valve and i beleive that is where a mixing valve would be in a more typical setup with a tank. I also played with the sytem a little last night and found my heater will shut down when the delta closes and flow is still present. It seems to be more of a safety feature and not ment to be used for normal modulation. It allowed it to over temp 5 degrees before shutting down then refired at 1-2 degrees below the set point
Oh yes ... I did see that pump initially ... my quick look this morning missed it.
Did the Co. you bought it from tell you how to pipe? The typical thing on a small system is close spaced "T" Pumping is towards on the boiler loop. The system is piped pumping away. This way the boiler gets what it wants as far as flow and the system pulls as needed. No bypass.
I would think it's just shutting down as the temp is met.
Sometimes is's best to look at a system and say. If money was no object and I wanted the most comfort ... what would I do? Then you reengineer it making it simple and cost effective to run.
My system works on three temps. The boiler loop ... the LLH temp and the temp at each manifold. The last should be close .. but this changes as the load increases (falling temps).
So you should be trying for the lowest water temp in the boiler loop and watch the temp out to the floor. Over time you will see the relationship.
As i said in an early post .. your savings will be marginal. Since the temps are close. It's just a fun exercise. About 20 years ago I bought a huge stone victorian in Chestnut Hill PA -- old huge boiler in the basement. I installed twin Buderus gas boilers with ODR and ran the system with constant circulation. So before it was heat on 190 degree water ... new way was send heat around at the temp the building needed. It rarely went above 150 .... huge savings. more comfort.
Now that my system is up and running and all the floors are warm -- the boiler was running at 99 degrees w/ 34 degree outdoor temps and mid 70 floor degree water at the loops. I forget the LLH temp .... the goal is to keep it all running so the floor never falls behind ..... but, to find that point initially you need to go past.
Most people in a garage because of design end up having more of an on and off situation ...
Yes it is plumbed exactly as the company recommended they referred to it as a closed direct primary loop system. I understand what you are saying about the constant flow. Now maybe it's just a little outside my education level but with me having no tank involved to bleed the stored energy from what advantage would constant flow be ? I can see the advantages if constant flow with an appropriately sized tank. That would obviously require a complete redesign of my above slab system. This is my first system so i left the design up to a professional the only real things that were dictated by me were budget and space concerns. I was out their last night from sons 4pm until close to 8 outside temps were in the mid 40's during the day and dropped to around 32 when i went in during that time the system only ran once for 3 minutes or lessOh yes ... I did see that pump initially ... my quick look this morning missed it.
Did the Co. you bought it from tell you how to pipe? The typical thing on a small system is close spaced "T" Pumping is towards on the boiler loop. The system is piped pumping away. This way the boiler gets what it wants as far as flow and the system pulls as needed. No bypass.
I would think it's just shutting down as the temp is met.
Sometimes is's best to look at a system and say. If money was no object and I wanted the most comfort ... what would I do? Then you reengineer it making it simple and cost effective to run.
My system works on three temps. The boiler loop ... the LLH temp and the temp at each manifold. The last should be close .. but this changes as the load increases (falling temps).
So you should be trying for the lowest water temp in the boiler loop and watch the temp out to the floor. Over time you will see the relationship.
As i said in an early post .. your savings will be marginal. Since the temps are close. It's just a fun exercise. About 20 years ago I bought a huge stone victorian in Chestnut Hill PA -- old huge boiler in the basement. I installed twin Buderus gas boilers with ODR and ran the system with constant circulation. So before it was heat on 190 degree water ... new way was send heat around at the temp the building needed. It rarely went above 150 .... huge savings. more comfort.
Now that my system is up and running and all the floors are warm -- the boiler was running at 99 degrees w/ 34 degree outdoor temps and mid 70 floor degree water at the loops. I forget the LLH temp .... the goal is to keep it all running so the floor never falls behind ..... but, to find that point initially you need to go past.
Most people in a garage because of design end up having more of an on and off situation ...
With the restraints of my system design. I can only do pulsed run times. Now I'm my head the dance becomes directly related to the pads ability to absorb and transmit said heat into the space. I could imagine that input btu vs heater output efficiency is not linear so their is going to be a balancing act between run time a x btu and the slabs ability to absorb and transmit that heat. From a comfort stand point long low temp runs are the obvious winner but on the fuel consumption front. In my head their are too many variables to be able to definitively say lower water temp (heater set point)is with out a doubt going yeild less fuel consumption. Time will tell and hopefully it's not too expensive if a learning curve lol.i hope this makes sense. Im not always good at writing my thoughts
With constant flow the water in the boiler loop is spinning around -- the boiler is happy and not shutting off because it is seeing the flow (water going through the heat exchanger) that it needs. It is seeing the proper flow -- because you have the proper pump.
The colder water comes into the boiler -- gets heated .. goes out ...
Now -- before that now hotter water can come back around to the circulator and boiler ... the system pump pulls the hot water out of the boiler loop ... the boiler loop circulator does not care as any lost water is being made up by the system return piping. It's a closed system remember.
So the two pumps work together .... The system pump can pull this hot water out to the radiant ... and will do so properly because you have the correct system circulator.
The benefit -- the radiant is always seeing heat. The goal is to give it just want it needs to heat the slab to the temp required -- to keep the space temperature what you want. The boiler loves it because it can run long and slow .. this is the most efficient way for them to run. That's why modulation saves fuel.
Your piping is unusual to me ... but again -- radiant can be very forgiving. Send a big burst of heat into a slab ...it will get warm and heat the space. You can do this over and over again with a slab sensor ... will it work (most likely) ... it's just not as efficient. I'm assuming the people you bought it from have experience with what they sell and the size system you have.
Take two other examples.
People use a tank water heater -- circulator and some PEX. In a small space it will work ... try and heat 2000sf and the typical water heater (gas) does not have enough BTU's (often 26k burner). The water heater will never shut off and never heat the slab. In a small space the pump will run and shut off ... and you can adjust the temp of the water as well.
Using an on-demand water heater in a small space. I see them piped with one circulator feeding 3 PEX loops. The circulator has enough power to both push the water through the heaters exchanger and send the water through the PEX. They cycle like crazy as you are now trying to put 150k of heat into a small space and the return water is too hot. But - they often work. Take that same heater and try and heat a 2000sf space and what happens. Normally the pump does not have enough Head to push the water through both the exchanger and the PEX. Now people can't figure out why the heater starts and shuts off all the time. Or does not start at all.
Both of the above examples cause problems ... Why? Lots of people copy others. So if it works in my friends shop why not mine? Well ...How big is your shop.
If you take a look at my system -- there is not much to it. It's still just two loops -- two pumps. Now, I'm trying to heat 5k sf of a house ... so to do that with comfort and efficiency requires more parts.
In my case it's a Viessmann boiler -- you can get the basic boiler for around $2500. It's all the rest of the items required that makes the systems expensive. This project has to run on propane .. Viessmann has the best burners when running propane. Propane is a dirty fuel vs natural gas. Again -- what you would do for a house is different than a shop.
I have another boiler that will be going in the rebuilt studio -- that system will be much simpler and will have some panel radiators. The floor will be set to ODR at a lower temp and the radiators can be manually modulated.
The colder water comes into the boiler -- gets heated .. goes out ...
Now -- before that now hotter water can come back around to the circulator and boiler ... the system pump pulls the hot water out of the boiler loop ... the boiler loop circulator does not care as any lost water is being made up by the system return piping. It's a closed system remember.
So the two pumps work together .... The system pump can pull this hot water out to the radiant ... and will do so properly because you have the correct system circulator.
The benefit -- the radiant is always seeing heat. The goal is to give it just want it needs to heat the slab to the temp required -- to keep the space temperature what you want. The boiler loves it because it can run long and slow .. this is the most efficient way for them to run. That's why modulation saves fuel.
Your piping is unusual to me ... but again -- radiant can be very forgiving. Send a big burst of heat into a slab ...it will get warm and heat the space. You can do this over and over again with a slab sensor ... will it work (most likely) ... it's just not as efficient. I'm assuming the people you bought it from have experience with what they sell and the size system you have.
Take two other examples.
People use a tank water heater -- circulator and some PEX. In a small space it will work ... try and heat 2000sf and the typical water heater (gas) does not have enough BTU's (often 26k burner). The water heater will never shut off and never heat the slab. In a small space the pump will run and shut off ... and you can adjust the temp of the water as well.
Using an on-demand water heater in a small space. I see them piped with one circulator feeding 3 PEX loops. The circulator has enough power to both push the water through the heaters exchanger and send the water through the PEX. They cycle like crazy as you are now trying to put 150k of heat into a small space and the return water is too hot. But - they often work. Take that same heater and try and heat a 2000sf space and what happens. Normally the pump does not have enough Head to push the water through both the exchanger and the PEX. Now people can't figure out why the heater starts and shuts off all the time. Or does not start at all.
Both of the above examples cause problems ... Why? Lots of people copy others. So if it works in my friends shop why not mine? Well ...How big is your shop.
If you take a look at my system -- there is not much to it. It's still just two loops -- two pumps. Now, I'm trying to heat 5k sf of a house ... so to do that with comfort and efficiency requires more parts.
In my case it's a Viessmann boiler -- you can get the basic boiler for around $2500. It's all the rest of the items required that makes the systems expensive. This project has to run on propane .. Viessmann has the best burners when running propane. Propane is a dirty fuel vs natural gas. Again -- what you would do for a house is different than a shop.
I have another boiler that will be going in the rebuilt studio -- that system will be much simpler and will have some panel radiators. The floor will be set to ODR at a lower temp and the radiators can be manually modulated.
With the restraints of my system design. I can only do pulsed run times. Now I'm my head the dance becomes directly related to the pads ability to absorb and transmit said heat into the space. I could imagine that input btu vs heater output efficiency is not linear so their is going to be a balancing act between run time a x btu and the slabs ability to absorb and transmit that heat. From a comfort stand point long low temp runs are the obvious winner but on the fuel consumption front. In my head their are too many variables to be able to definitively say lower water temp (heater set point)is with out a doubt going yeild less fuel consumption. Time will tell and hopefully it's not too expensive if a learning curve lol.i hope this makes sense. Im not always good at writing my thoughts
Well if the heater can really run at efficiency -- down to 17k ... you should be able to get longer run times from it.
One of the hits against -- constant circulation. Years ago ... fuel was cheap and pumps very inefficient. Why would you want to have constant ... and how would you control the temps. I saw system years ago with 5 pumps -- even small they were 500w running 24/7. That's a lot of electric to push water around -- but, people wanted comfort. There were always better ways to do it ... but, more pumps is easier to do and requires no "thinking "
Modern pumps changed all of this -- it's not unusual for them to be using under 20w. My system uses about $12 a month in electric .. the system pump using between 25 and 45w depending on zones open
Yes the people who designed it use this particular setup quite a bit i beleive the key is the heaters large range of adjustability when my system is running it has no problem maintaining the set point. I use burst to describe functionality but it works a little more seamlessly than that. As i said depending on outside temps it will run anywhere from 3-6 minutes on an average cycle and these range from 35 minutes apart to a few hours depending on outside conditions. During a cycle the heater maintains 109 degrees outlet and the return water temps typically start in the high 60's to low 70's and reach mid 80's by the end of cycle. Since we are in the same fuel. And seem to be dealing with similar weather conditions( im in Central Maryland) do you mind sharing some average fuel consumption numbers. I'm only in week three so i don't have any solid numbers yet. The only thing i have to compare to is my house and it's on oil. So other than dolars to area heated it's not apples to apples by any meansWith constant flow the water in the boiler loop is spinning around -- the boiler is happy and not shutting off because it is seeing the flow (water going through the heat exchanger) that it needs. It is seeing the proper flow -- because you have the proper pump.
The colder water comes into the boiler -- gets heated .. goes out ...
Now -- before that now hotter water can come back around to the circulator and boiler ... the system pump pulls the hot water out of the boiler loop ... the boiler loop circulator does not care as any lost water is being made up by the system return piping. It's a closed system remember.
So the two pumps work together .... The system pump can pull this hot water out to the radiant ... and will do so properly because you have the correct system circulator.
The benefit -- the radiant is always seeing heat. The goal is to give it just want it needs to heat the slab to the temp required -- to keep the space temperature what you want. The boiler loves it because it can run long and slow .. this is the most efficient way for them to run. That's why modulation saves fuel.
Your piping is unusual to me ... but again -- radiant can be very forgiving. Send a big burst of heat into a slab ...it will get warm and heat the space. You can do this over and over again with a slab sensor ... will it work (most likely) ... it's just not as efficient. I'm assuming the people you bought it from have experience with what they sell and the size system you have.
Take two other examples.
People use a tank water heater -- circulator and some PEX. In a small space it will work ... try and heat 2000sf and the typical water heater (gas) does not have enough BTU's (often 26k burner). The water heater will never shut off and never heat the slab. In a small space the pump will run and shut off ... and you can adjust the temp of the water as well.
Using an on-demand water heater in a small space. I see them piped with one circulator feeding 3 PEX loops. The circulator has enough power to both push the water through the heaters exchanger and send the water through the PEX. They cycle like crazy as you are now trying to put 150k of heat into a small space and the return water is too hot. But - they often work. Take that same heater and try and heat a 2000sf space and what happens. Normally the pump does not have enough Head to push the water through both the exchanger and the PEX. Now people can't figure out why the heater starts and shuts off all the time. Or does not start at all.
Both of the above examples cause problems ... Why? Lots of people copy others. So if it works in my friends shop why not mine? Well ...How big is your shop.
If you take a look at my system -- there is not much to it. It's still just two loops -- two pumps. Now, I'm trying to heat 5k sf of a house ... so to do that with comfort and efficiency requires more parts.
In my case it's a Viessmann boiler -- you can get the basic boiler for around $2500. It's all the rest of the items required that makes the systems expensive. This project has to run on propane .. Viessmann has the best burners when running propane. Propane is a dirty fuel vs natural gas. Again -- what you would do for a house is different than a shop.
I have another boiler that will be going in the rebuilt studio -- that system will be much simpler and will have some panel radiators. The floor will be set to ODR at a lower temp and the radiators can be manually modulated.
Yes the people who designed it use this particular setup quite a bit i beleive the key is the heaters large range of adjustability when my system is running it has no problem maintaining the set point. I use burst to describe functionality but it works a little more seamlessly than that. As i said depending on outside temps it will run anywhere from 3-6 minutes on an average cycle and these range from 35 minutes apart to a few hours depending on outside conditions. During a cycle the heater maintains 109 degrees outlet and the return water temps typically start in the high 60's to low 70's and reach mid 80's by the end of cycle. Since we are in the same fuel. And seem to be dealing with similar weather conditions( im in Central Maryland) do you mind sharing some average fuel consumption numbers. I'm only in week three so i don't have any solid numbers yet. The only thing i have to compare to is my house and it's on oil. So other than dolars to area heated it's not apples to apples by any means
My particular system is new as well .... so I don't have fuel usage.
Getting slab temps at different points would be interesting ....
It would also be interesting to know how the water heater works __ 17k is very low for an on demand. Most start out on high and come down ... but 17k is not much when you are trying to heat domestic water in one pass.
It sounds like it is firing on high -- 3 to 6 min is not a lot of time .... so it has to be just heating around the pipe and shutting off and the slab then gives off heat.
As I said -- mine was heating 5k sf of house to the upper 60's at 99 degree water output. The max output of the unit is under 70k BTU. The house is still under construction and not all tight ... so the slope will change once we are in.
Most water heaters manufacturers don't publish the efficiency ratings where you need to see them. A ModCon boiler will have graphs showing efficiencies ... it's also a given that lower is better ... plus you get the Condensing (the Con ) in ModCon.
stingry
Well-known member
People use a tank water heater -- circulator and some PEX. In a small space it will work ... try and heat 2000sf and the typical water heater (gas) does not have enough BTU's (often 26k burner). The water heater will never shut off and never heat the slab. In a small space the pump will run and shut off ... and you can adjust the temp of the water as well.
I beg to differ! I heat 3600 sq ft with a 75 k btu 75 gallon hot water heater. My heat load calculator called for 50 k btu at a design temp of -12 degrees. I intentionally oversized by 50%. My system works extremely well, running very seldom to maintain 65 degree air temperature. I have 12 loops with two zones, each with it’s own circulator and thermostat. We can have some very cold temps here in Western Nebraska, single digits and below zero not uncommon. In the coldest months, my combined ng and electricity bill is around $100. A very simple and economical system. A well designed radiant floor system utilizing a hwt can be effective and economical. I do agree with you on the pitfalls of the on demand heaters being the reason I used the tank heater.
I beg to differ! I heat 3600 sq ft with a 75 k btu 75 gallon hot water heater. My heat load calculator called for 50 k btu at a design temp of -12 degrees. I intentionally oversized by 50%. My system works extremely well, running very seldom to maintain 65 degree air temperature. I have 12 loops with two zones, each with it’s own circulator and thermostat. We can have some very cold temps here in Western Nebraska, single digits and below zero not uncommon. In the coldest months, my combined ng and electricity bill is around $100. A very simple and economical system. A well designed radiant floor system utilizing a hwt can be effective and economical. I do agree with you on the pitfalls of the on demand heaters being the reason I used the tank heater.
Typical = 40g .. they have a 26K burner at 80%. You have a 75k BTU -- the tank size really does not matter much ... but more water in the tank will act as a buffer against the burner time and the standby loss is into the space. Often a vent damper if it's atmospheric will save some $$
You also have a well insulated space. I have been asked more than once to look at a system where the person did not understand what a typical water heater has as an output. It's not magic -- heat in heat out. The time factor (run time) is all dependent on the BTU's the system needs and what you are giving it.
Also -- what's the life of a 75K power vent water heater? + they are not cheap ($1300). There is no one way to do it. Example: You have two pumps. It could also be one smart pump and two zone valves. Or one smart pump and a single manifold with controls on the zones.
How long will you be in a space -- whats the payback with more efficiency. The key to your system working is the building was well constructed and you did a heat load so you understood what you needed