Boiler/pump settings for in floor

[Smrtpunk]

What temperature are you setting your boilers at for in floor heat?

I seem to remember setting mine to the lowest setting available (115F) as per the manufacture's instructions. I wonder however, if setting it higher would result is a faster heat up time in my shop?

Thought's? Any reason why the lowest setting. Also, what speed do you run your pumps at?

 

[phansen39]

Even 115 is pretty hot for infloor heat. You say heating the shop. Sounds like you turn it off. A heating system like this is designed to be left on at a steady temperature. Takes a long time to heat the concrete slab.

 

[finn]

Set it to around 100 -115 degrees F, max.

If you need to swing the temperatures, Invest in a hanging heater and use that to bring the room temperature up.

Radiant systems aren’t compatible with changing thermostat settings because of their inherent slow response rates. They are best for buildings that have to be heated to a set temperature 24/7.

 

[Smrtpunk]

Set it to around 100 -115 degrees F, max.

If you need to swing the temperatures, Invest in a hanging heater and use that to bring the room temperature up.

Radiant systems aren’t compatible with changing thermostat settings because of their inherent slow response rates. They are best for buildings that have to be heated to a set temperature 24/7.

I have heard that before and have in fact purchased another hanging heater.

However, there's times where I would like to heat the building up with just the floor heat and it would be nice for it to take less than a day to move 5 degrees.

 

[yeldogt]

You can increase the temps initially ....... return it to the lower temps once the floor warms up ... what type of boiler?

A thick slab w/ 12" spacing will take a while to heat. Closer spacing increases response.

It's better to maintain some level of heat in the slab and increase temp when needed with another type of heater

 

[mygarageone]

I knew this would be an issue in my garage , so I ran my tubing 8" on center rather than the recommend . Makes heating the garage from a cold temp to a comfortable temp very quick. And I can run my operating temps below 105 ,I do however keep my garage heated yr around .

 

[Chris705]

I think pump speed/gpm setting wants to be closest to where you get about twenty degrees difference between you supply and return water temps... I believe the reason for this is to allow the slab to absorb the heat...return water that is warmer means its running thru the tube too fast (wasting energy), colder return and you aren’t getting even heating.

 

[GrayFlattop]

FWIW, I use a Tekmar boiler control with outdoor reset. The Tekmar control uses a variable speed mixing pump that delivers the correct water temp for indoor temp desired. For this to work, you need a primary loop (high temp) and a secondary loop (low temp) The primary loop would be used for indirect water heaters . radiators, baseboards and the secondary loop would be used for in-floor tubing (you can add a setpont for a max temp in the secondary loop - typically 130F.

No question it requires a bit more $ to set things up this way, but the results are just fantastic. Tekmar has some very good technical resources for system design - start here: http://www.tekmarcontrols.com/support.html

 

[raspy]

It's best to know what type of boiler and what the plumbing scheme is being used before answering that question. Standard boilers must be allowed to operate above their condensing temperatures, while condensing boilers can be set at very low settings. If the boiler is only sized large enough to compensate for the losses of the building, the setting will be practically meaningless as it will constantly be overloaded during warm up.

If the boiler is set higher, it still should be set low enough so that if someone turns the thermostat all the way up it won't destroy the flooring and kill the fish, etc.

The final thing is whether or not the house is set on constant circulation or not.

I never run constant circulation, so I want good response when I call for heat. My systems use condensing and modulating boilers with about two or three times the capacity of the heat loss of the house. So I set them at about 126* in new houses for good response with setback thermostats. My own house is set at 130* in a non modulaing boiler with a 10* differential controller. For an area that is thermostat controlled, but without setback, 100* should be fine. If you have an injection system or you modulate the delivery temp independent of the boiler high limit, you must set the boiler high enough to feed the highest temp the modulating system will allow and at the same time keep the boiler above it's condensing temp, if it is a conventional boiler.

Bottom line: 100 - 120 will always be enough to actually heat the house assuming conventional in-slab design. Constant circulation will be considerably cooler. The average floor temp only needs to be about 70* to be comfortable in living areas. Never more than 80* even in bathrooms. Workshops and sleeping areas are often fine at about 65* That is not the delivery temp, it's the average temp across the floor.

 

[Smrtpunk]

It's best to know what type of boiler and what the plumbing scheme is being used before answering that question. Standard boilers must be allowed to operate above their condensing temperatures, while condensing boilers can be set at very low settings. If the boiler is only sized large enough to compensate for the losses of the building, the setting will be practically meaningless as it will constantly be overloaded during warm up.

If the boiler is set higher, it still should be set low enough so that if someone turns the thermostat all the way up it won't destroy the flooring and kill the fish, etc.

The final thing is whether or not the house is set on constant circulation or not.

I never run constant circulation, so I want good response when I call for heat. My systems use condensing and modulating boilers with about two or three times the capacity of the heat loss of the house. So I set them at about 126* in new houses for good response with setback thermostats. My own house is set at 130* in a non modulaing boiler with a 10* differential controller. For an area that is thermostat controlled, but without setback, 100* should be fine. If you have an injection system or you modulate the delivery temp independent of the boiler high limit, you must set the boiler high enough to feed the highest temp the modulating system will allow and at the same time keep the boiler above it's condensing temp, if it is a conventional boiler.

Bottom line: 100 - 120 will always be enough to actually heat the house assuming conventional in-slab design. Constant circulation will be considerably cooler. The average floor temp only needs to be about 70* to be comfortable in living areas. Never more than 80* even in bathrooms. Workshops and sleeping areas are often fine at about 65* That is not the delivery temp, it's the average temp across the floor.

It's an electric boiler, I believe it's a 4 KW unit. It uses a 40amp 240 breaker to operate.

It's thermostatically controlled to 5 degrees (C) at all times. I have an auxiliary 30 amp 240 electric fan heater as my secondary means to heat the building (16*37) when I go out there to work.

Thing is and this is where it mostly becomes an issue. My secondary fan heater shares the same electrical CCT as my electric beer brewing equipment... So on days where I'm brewing beer, I only have the floor heat to rely on.

Right now, on colder days, It takes hours, I mean like 8-10 hours non stop running to bring the room up to 10-12 degrees (C) from 5 (C).

If raising the temp of the water could mean a decrease in the time it would take to gain room temperature, then I say why not?

 

[raspy]

Raising the water temp, in your case will not make a difference in the recovery time. You are only adding about 12,000 BTU to your system and that is very low. In this case it's not the temp that counts, it's the Watts or BTUs that count, and your delivery is low. The boiler will always be in an overloaded condition and unable to come up to a higher delivery temp. It will always be putting it's full output into the system when on.

My previous post assumed a gas boiler was being used. With electric, there is no condensing or tempering to worry about.

 

[Radix2]

It's an electric boiler, I believe it's a 4 KW unit. It uses a 40amp 240 breaker to operate.

It's thermostatically controlled to 5 degrees (C) at all times. I have an auxiliary 30 amp 240 electric fan heater as my secondary means to heat the building (16*37) when I go out there to work.

Thing is and this is where it mostly becomes an issue. My secondary fan heater shares the same electrical CCT as my electric beer brewing equipment... So on days where I'm brewing beer, I only have the floor heat to rely on.

Right now, on colder days, It takes hours, I mean like 8-10 hours non stop running to bring the room up to 10-12 degrees (C) from 5 (C).

If raising the temp of the water could mean a decrease in the time it would take to gain room temperature, then I say why not?

What are the supply and return temps to the boiler right now when the floor is heating up? Is the flow low enough that when the floor is at 5c, the boiler is able to supply water at its setpoint? Very often when heating from a low temp, the boiler is not able to hit its setpoint anyway, so it will not matter if you set it higher.

 

[finn]

One boiler I had mandated a primary- secondary piping system to minimize thermal shock to the heat exchanger. We plumbed my new boiler (different building) with the primary secondary.

Works well.

 

[yeldogt]

You simply don't have enough capacity to do what you want to do -- it's like standing in your house with a hair dryer.

If the space is well insulated ... try a combination of the floor heat at a higher set temp and the fan heater.

I'm in cold climate ... it's been in the 20's at night for months. We use constant circulation and a boilers sized for the load. The 20 degree difference supply/return is to maintain a uniform slab temp

 

[Smrtpunk]

You simply don't have enough capacity to do what you want to do -- it's like standing in your house with a hair dryer.

If the space is well insulated ... try a combination of the floor heat at a higher set temp and the fan heater.

I'm in cold climate ... it's been in the 20's at night for months. We use constant circulation and a boilers sized for the load. The 20 degree difference supply/return is to maintain a uniform slab temp

I don't buy into this idea that I'm maximizing my output on the heater as the system barely runs...

I swear as long as it's set to 5C I almost never walk into the garage and see it running. I could probably check the data log from my electricity company to see what times it's running in the middle of the night as it would be easy to track since we would have almost nothing on. but like I say, it seems to be barely running, unless I crank it at which point it runs for hours to make heat.

I'm going to check the differential on the pipes and see what I come up with. So far, I feel that no one has made a very solid argument to run the system as intended at a lower temp. Seems to me that a higher temp would result in the room heating faster.

 

[yeldogt]

Well 5C .. 41 degrees to us south of you is cold. Getting that slab and space up 12 degrees C takes many BTU's ... more than you have available. Thats 61 degrees! Maintaining a temp is not the same as raising a temp .. especially at 41 degrees. You only have 4kw.

When you turn that unit on ... the water coming back is cold. It's on or off w/ the temp set point being the limit. Whats controlling the system.

Even a gas or oil boiler with 7 times the output would need to run a while before it was able to get high return temps in the tubes at 41 degrees.

 

[raspy]

Well 5C .. 41 degrees to us south of you is cold. Getting that slab and space up 12 degrees C takes many BTU's ... more than you have available. Thats 61 degrees! Maintaining a temp is not the same as raising a temp .. especially at 41 degrees. You only have 4kw.

When you turn that unit on ... the water coming back is cold. It's on or off w/ the temp set point being the limit. Whats controlling the system.

Even a gas or oil boiler with 7 times the output would need to run a while before it was able to get high return temps in the tubes at 41 degrees.

Yeldogt is exactly right.

When a boiler is severely overloaded, you don't have the luxury of calling out the in and out temps or trying for a 20* differential, etc. You are just adding all the power you have, over a long period, to raise the overall room temp. All the while, you are fighting losses to the environment and changing the temperature of tons of concrete. It's a big job with a little tool.

BTUs and watts are equal to horsepower. Raising a temperature is equal to going up a hill. Try towing a logging truck with a VW Bug and discover how it takes all day to get up a grade. Or light a match and stand in the room waiting for the temperature to go up. The match is very hot, but the room doesn't change much. The room's rise rate doesn't have much to do with the temperature of the match, it's the total BTU output of the match that is important. Same with your boiler.

Turn the outlet temp up on your boiler and then measure what is happening while it's running, to satisfy yourself. It's really not a debatable situation, just simple physics, do some testing for yourself, rather than waiting to be convinced.

The reason your boiler is not running very much, until you raise the thermostat, is because your room is so cold that it doesn't have much loss to the environment. Raising the temp, and then holding it there, is more difficult.

 

[Jackfre]

This may be a pump issue as well. How long are your loops and what size? Reverse returns on the loops? Does the slab warm consistently across all zones? How big is the space and how well is it insulated? Slab edge insulation? Your 4 kw unit is max input of 13200 btu. That is not a lot for radiant slabs.

 

[Smrtpunk]

I ran the system for a while last night then checked the temps on the feed and return hose with my infrared thermo, it read 66F feed and 60F return. If my math is right, thats a 10 percent differential.

I decided to crank the machine to 150F and ran it for 30 mins before checking again and the results were 67/62. I then checked the pump speed and noticed it was at its fastest setting, I dropped it down to med and have yet to run a test.

According to some of the comments made my temperature differential is not ideal, hopefully changing the speed will bring it more into a favorable 20% difference. Also, I'm guessing the boiler is struggling to reach its temp setting which is what many people here were saying.

I'll try to run some more testing with the slower pump temperature to see how it goes.

 

[raspy]

Smrt,

I think you are still missing the point.

20* is a random number that is better than 30* or 50*, etc. It is not, in itself "ideal". The point is that the larger the differential, the more uneven the heat and the more thermal shock in the boiler, not that you are out of the "ideal" range and that that is why you are not getting the performance you seek.

You are getting all the energy that your boiler can produce, delivered to the floor, and your 6* differential means nothing other than it tells you the boiler is overloaded and you are delivering all it can produce.

For some reason, it seems you want your boiler to produce more than it can or you don't understand that it is doing all it can. The numbers you posted make perfect sense (only a 5 or 6* differential), for a system that has a very slow recovery rate. A large differential would mean you are not delivering all the energy, or all the energy evenly, a small differential means you are.

You can test this, if you wish and as I previously recommended. Restrict the flow gradually with one of the valves on the delivery lines. As you do the differential will gradually increase. Eventually the differential will get to be so much that the boiler will cycle off as it reaches it's high limit. At that point, you will be delivering less overall, because the boiler will be spendong some of it's time off. See what I mean?

And again, this is not a contest to convince by presenting the best argument. It's basic boiler function and heat absorption. You need to look more carefully and experiment more to get results for yourself. See what you get and try to figure out what it means.

More restricted flow means more differential and less even heating. More restricted flow means more OFF time for the boiler which means slower recovery.

Less restrictive flow means less differential. Less restriction means more even heating and more energy delivered over time.

20* differential is NOT a magic number in any way. it's a common number used as a reference that is better than a higher number, but not better than a lower number. A compromise. It only comes into play when the boiler has enough power and the flow is slow enough, to cause some other problem, such as thermal shock or uneven heat. In your case, the problem is not enough BTUs from the boiler to have a reasonable recovery rate. The problem is NOT the differential. You are wasting your time looking for ways to make it produde more than it can. Better to think about what the numbers actually mean and experiment for yourself to better understand.

Please re-read post 17 about heating a room with a match. Look up BTU (British Thermal Unit) and think about how temperature is only one of the factors in that calculation. You can always fake it and get a higher delivery temperature by restricting the flow, you can always adjust to a higher differential, but those means nothing as far as total energy delivered.

 

[yeldogt]

I ran the system for a while last night then checked the temps on the feed and return hose with my infrared thermo, it read 66F feed and 60F return. If my math is right, thats a 10 percent differential.

I decided to crank the machine to 150F and ran it for 30 mins before checking again and the results were 67/62. I then checked the pump speed and noticed it was at its fastest setting, I dropped it down to med and have yet to run a test.

According to some of the comments made my temperature differential is not ideal, hopefully changing the speed will bring it more into a favorable 20% difference. Also, I'm guessing the boiler is struggling to reach its temp setting which is what many people here were saying.

I'll try to run some more testing with the slower pump temperature to see how it goes.

When you decided to "crank" all you did was allow the unit to run until it hit 150 .. the unit is not big enough to ever get to that temp. The unit is on or off .. it's not like a car engine where you can push down on the pedal and get more out of it. That's why the numbers did not change ...

 

[finn]

Six degrees measured at sixty degrees isn’t a ten percent change.

The scale would probably have to start at absolute zero and run to infinity if wanted to use percentages in temperature comparisons... in any event, percentage means nothing in this case.