Calling all in floor heat users

[dirttracker18]

I know this issue has been beat to death so what I am looking for is some real world experiences.

I currently have in floor heat using an electric hot water heater. I took about a year to get the system balanced out and I think I am getting about the best I can out of the system as it sits.

I have recently found what I think is a good deal on a Hydro Shark III 12KW unit at $565.

So first questions is, is this is a good price for this unit. It seems so from what else I can find on it.

Second question is for those that have made the switch from hot water heaters to on demand units. Did you see any significant imporvemnt in electrical usage?

I believe my current set up has a difficult time keeping up with demand. I start to lose input temps before the pump shut offs. So I am running out of "hot" water before the temp in the shop comes up and am using warm water now instead. As well I cannot get the input temps I want. The best I can do is 90* input and not run out of hot water before the pump shuts down. Even at that my temps drop.

So back to the questions, is this a wise investment in that I can save money in the long run? I realize there should be savings just by not having to keep a tank full of water hot but how much overall?

Any thoughts?

 

[Fastback]

Do you have the elements tied together? You may want to try that before spending more money.

Can you tell me more about your slabs size and loop length?

I dont have a hydroshark but I have a really cheap on demand unit... I have always read that a BTU is a BTU,so having a 12kw hydroshark versus a tank heater with two 6k elements strapped together for simultaneous runtime should be the same thing, the difference being the size of the tank and any heat loss that it gives up.

I run about 110 in with my 11kw Titan, I have a 720' slab 6" thick with two loops, if I was doing it again I would have three loops, that would give me a higher delta-T. the 11kw unit can send in 140 fluid if I want but I still have a wide delta.

My thermostat basically switches the pump, and then flow dictates that the heater turn on. I cant just circulate warm water through my slab at all, I kinda wish I could have a small tank because then I could use a solar tube collector and maybe a wood heater to heat that tanks supply and let the pump have all of the 100 degree water it wants.

I guess I just dont see a big negative to having a tank, provided that its not a huge amount of expensive antifreeze.

 

[00si2]

http://cgi.ebay.com/Electric-Radian...801?pt=LH_DefaultDomain_0&hash=item3f0623e6d9

I just purchased 2 24kw units off of this seller in the last couple months. This is a little cheaper than you mentioned.

 

[dirttracker18]

http://cgi.ebay.com/Electric-Radian...801?pt=LH_DefaultDomain_0&hash=item3f0623e6d9

I just purchased 2 24kw units off of this seller in the last couple months. This is a little cheaper than you mentioned.

Actually that is the one I am looking at and from that seller.

HS Unit $527

Shipping $22

Cost to pick up at the border $15

Thats where I arrived at the $560 figure.

Anyone that has changed from a hot water tank to a tankles boiler that can share their results? Was it worth the change for you?

Fastback, I have tied the elements together and am heating 1200 foot slab 30 X36 garage with 12 foot ceilings. I have 5 loops.
The issue seems to be that I run out of 'hot' water before the air temp comes up. I am them heating the floor with warm water, 10 to 15* cooler then I started with.

 

[danski0224]

That's what happens when people try to DIY heating and cooling stuff without figuring out their required loads. Oops.

How big is the tubing in your loops? How long are the loops? Just looking at "5 loops" and "30 x 36", I'm guessing you are short on loops/too far apart and/or too long on length. If you don't have 5/8" tube and/or exceed 300 feet per loop, you have a problem that can't be fixed with a bigger water heater.

Do you know how many BTU's you need?

Do you know how many BTU's you are getting from your current water heater with the elements tied together?

How many BTU's will the tankless deliver? And more importantly, is it enough?

 

[dirttracker18]

Actually the system was well planned out but I choose to go with the hwt because I had it just sitting there as opposed to buying an on demand boiler. The system itself functions well, but once again the tank runs low on 'hot' water before the cycle ends.

No to offend but I am really not looking for advice on the system but real world observations from those that made the switch from hwt to boilers.

Is the efficiency of the boiler worth the switch or is the pay back too long term to be concerned.

In addition to the already mentioned information, electricity is not cheap around here, infact some of the most expensive in Canada. So any savings from better efficiency are magnified but a higher price. However I do not have access to NG and use propane for the house, which is also expensive here at $3.22 a gallon right now and rising.

 

[danski0224]

Actually the system was well planned out but I choose to go with the hwt because I had it just sitting there as opposed to buying an on demand boiler. The system itself functions well, but once again the tank runs low on 'hot' water before the cycle ends.

No to offend but I am really not looking for advice on the system but real world observations from those that made the switch from hwt to boilers.

Is the efficiency of the boiler worth the switch or is the pay back too long term to be concerned.

In addition to the already mentioned information, electricity is not cheap around here, infact some of the most expensive in Canada. So any savings from better efficiency are magnified but a higher price. However I do not have access to NG and use propane for the house, which is also expensive here at $3.22 a gallon right now and rising.

There is no efficiency difference between an electric water tank and an electric boiler, excluding stand by losses.

As far as turning electrons to heat is concerned, both are 100% efficient.

I suspect that the on demand unit you mentioned is at least 2x the capacity in kWh of your tank style electric water heater.

Not to offend, but if you do not know the load requirements of your heating system, and if the installed system is incapable of properly heating the space, the on demand system will cost you a whole shitload more to operate because it will be on all the time trying to heat a space that it can't.

There is a great deal of stored energy in your water tank. It is a crutch for your existing system.

You may be better off to add a second electric water heater tank.

There is no way to answer your question unless you know how many btu's you need, and is your existing system capable of delivering them. Based on your description, I don't think it can.

 

[Fastback]

Well, you have not told us how many KW the heater you have is per element or otherwise, so how can anyone answer your question?

 

[dirttracker18]

The question is for anyone that has switched from a hwt to an on demand boiler. Was it worth the switch.
A btu is a btu may very well be true but in this case the on demand unit can produce a constant temp of water while the hwt can only offer what is in storage. If the demand to bring the temp back up is more then the stored capacity of the hwt then the cycle runs a lot longer with less temp in the water. The hwt could never reheat fast enough if the demand is equal to what is in the tank.

In the intial design stage the hwt was speced as enough btu for the need. However, you cannot just compare btu's when talking in floor heat with a hwt or an on demand boiler. It is comparing apples to oranges. The tanks has "X" amount of stored heat capacity while the on demand unit can produce "X" temperature water indefinitely. The savings from not storing unneeded hot water and the fact that the on demand unit will modulate and not use all of the available 12kw makes the savings a no brainer. A 9kw unit will work for the space and heat loss but just barely. In a cold snap of below -30 c (which we get here) the 9 kw unit would really be taxed to keep up. Since the unit can modulate as needed, teh small extra cost for the 12kw seems reasonable and called for. Not too mention the planned shop expansion in the future (5 to 8 years).

All things being equal, in theory the on demand unit should out perform the hwt as far as electricity use, all things being equal. The only factor is initial cost which for me was nothing, that made it worthwhile to start with the hwt.
Can in floor heating be done with a hwt? The answer is yes. Is it optimal? The answer is no. There is no question about that.

My only question now is are the cost savings (all things being equal) with the on demand unit worth it in the long run for those that made the switch.

 

[Possum]

Sent you a PM earlier today.

 

[Fastback]

The question is for anyone that has switched from a hwt to an on demand boiler. Was it worth the switch.
A btu is a btu may very well be true but in this case the on demand unit can produce a constant temp of water while the hwt can only offer what is in storage. If the demand to bring the temp back up is more then the stored capacity of the hwt then the cycle runs a lot longer with less temp in the water. The hwt could never reheat fast enough if the demand is equal to what is in the tank.

In the intial design stage the hwt was speced as enough btu for the need. However, you cannot just compare btu's when talking in floor heat with a hwt or an on demand boiler. It is comparing apples to oranges. The tanks has "X" amount of stored heat capacity while the on demand unit can produce "X" temperature water indefinitely. The savings from not storing unneeded hot water and the fact that the on demand unit will modulate and not use all of the available 12kw makes the savings a no brainer. A 9kw unit will work for the space and heat loss but just barely. In a cold snap of below -30 c (which we get here) the 9 kw unit would really be taxed to keep up. Since the unit can modulate as needed, teh small extra cost for the 12kw seems reasonable and called for. Not too mention the planned shop expansion in the future (5 to 8 years).

All things being equal, in theory the on demand unit should out perform the hwt as far as electricity use, all things being equal. The only factor is initial cost which for me was nothing, that made it worthwhile to start with the hwt.
Can in floor heating be done with a hwt? The answer is yes. Is it optimal? The answer is no. There is no question about that.

My only question now is are the cost savings (all things being equal) with the on demand unit worth it in the long run for those that made the switch.

Whatever. I think you may find the on demand heater will run a lot more than what you have been used to, the ONLY difference will be where the heat is stored, the floor is will the storage instead of your current tank, you could obtain the same results with what you have now but you obviously dont want to hear it.

Good luck.

 

[dirttracker18]

Actually I would be interested in hearing why you believe that the on demand boiler would run longer then the current set up with the hwt. I am having a difficult time understanding why it would run longer? If the boiler produces heat at the same temp as the hwt provides, why would that cause the boiler to run longer?
Wouldn't the cycle be the same length? In theory (well as I see it anyway) if the hwt is running out of 'hot' water before the cycle ends, why would the boiler run longer? Would it not run for a shorter period of time since it can rpovide the correct temp?
What am I missing here?
Thanks

 

[Fastback]

What is a "Correct temp"? .

Im still curious what the total size of your current heater is so I can compare apples to apples, sure you could go with a monster electric on-demand and "Think" you have it dicked, but you may be wrong. What size is your current unit as far as KW ?

I took my heater apart, its just two hot water heater elements in a threaded tube no bigger than the nut size on the element (1"), the tubes are connected with a restrictive tube size to retain the fluid in those tubes long enough to be blasted with heat, it is 12kw.

I understand that my heater cannot run out of hot water so long as power is going to it, but that does not translate into efficiency.

 

[CADPoint]

I do and don’t have an interest in this post! I’ll take the blows for my remarks.
I’ll take them where they land!

The OP says that it was well planned out, but just went with the H20 heater they had sitting around, as implied these units aren’t designed to be commissioned for such a task required by the scope of this project. No mention of this H2O heater size was given.

Your system needed to be designed for the most critical usage IE days of low temperatures!

Your real key here is what is the returning temperature on your returning loops.

This will determine your required requirements to reheat to a desired level. Prime is understanding this output rate of the H2O heated, output verses
the input of the requirment of heating concrete, then yes you might well be short.

In no way is the floor loops a storage nor is the concrete. The loops are a means to disperse the heat to concrete. A big consideration is the heat loss or the heat transfer coefficient of concrete, but that’s not it either it’s really the heat transfer by convection.

The heat is dispersed to the concrete and needs to be replaced constantly. It’s coefficient is .42 for light concrete, portland cement .29 (.5 is considered poor -in respects to co efficiency,.8 is only fair), heat is hardly going to be stored in concrete.

In talking to other parties, the equation for a complete understanding of an HVAC system can be the breath of a page, I don’t know the complete equation that you’d need for you OP. But there is an answer!

The answer lies on the other forums that are devoted to your subject matter!

There’s no evading the fact that math is involved here. Plugging the wrong number in here or there can drastically change the sum, or in the OP’s case the wrong desired result.

We (ok- some of us might) daily deal mostly with end results summary equations of A=B/C, this in not the case for the OP.

You say you maxed/tweaked it to the max, and it’s still not right, the numbers exist and you are either stuck with the wrong numbers and or don’t understand where to correct your numbers.

My suggestion is that you get an engineer in their and crunch some math, somebody has missed something!

This Page helped me compile my thoughts as presented but is not in direct answer to your problem.

 

[Possum]

Some of you guys have come a long ways in a month to be busting a guys balls over this question... http://www.garagejournal.com/forum/showthread.php?t=86439

Seems like most electric water heaters I have encountered have two 4500w elements, tied together that would be the same figure as the 9KW or 31000 BTU's that he stated the garage required. That number doesn't sound too far off for 1100 square feet Southern Canadian garage with at temp delta of 60F or -10F outside to and 50F inside (assumptions). If hes right on the edge of capacity with the 9KW tank water heater then the max 12000w that this unit has may be just the few more BTU he needs. Back to his question of is there and advantage to a tankless heater that has a recovery rate in gallons per minute for a given flow, or a tank type that is more of a gallons per hour rating? Instead of the return water being mixed with the hot water in storage and lowering the output temps, is it better to heat the returning water to a constant as it comes back with a modulating element? He hasn't listed all his specs on the system, so we can't really make any assumptions if its right or wrong. It stated that its "well thought out" so maybe its an engineered system that ended up with a bit to small but economical at the time heat source to start out with? If its working now, I bet it will function better with a boiler with an extra 10000 btu's . Will he see any savings over the tank type? Probably not.

 

[Fastback]

Some of you guys have come a long ways in a month to be busting a guys balls over this question... http://www.garagejournal.com/forum/showthread.php?t=86439

Hey, I was honest about what I wanted to do, I learned everything I could and built it, and mine works. This guy wants to know if one is better than another in his system that does not work, and yet we have no real info.

If you think I or anyone else here was ballbusting you must live in a church.

Im done with this thread, its pointless.

 

[dirttracker18]

You don't need my system info to tell me about your experience when you changed from a hwt to an on demand system.
That's all I was looking for, not a critique of my system or knowledge.

I have seen many posts where guys have stated they started with a hwt and switched to an on demand unit. I just wanted to know how the change over worked out for them and if they felt it was a good idea. Did they save money?

Fastback, mine works too. In fact it heats just fine. But now that I have it all fine tuned and have put a lot of thought into how it works, why and when, I can see that it cold run better (read cheaper). I saved money on the initial build but would now like to save money on the long term operation.

Anyone that made the switch care to chime in with their results?

 

[sneezer41]

The problems people have using tankless water heaters relates to their restriction of flow in order to raise temp. a tank does not restrict flow in this way

your idea of increasing 'efficiency' with a tankless is flawed. the only way a tankless is more efficient than a tank is standby losses. think now, where is the heat going from the standby losses in your tank type? Into the garage.......

when using a hot water heater for its stated purpose, this is waste because you do not want to heat the space, only the water, but in this case you want to heat the space, so an electric[tank] hot water heater is exactly as efficient as an electric tankless because all of its 'waste' heat ends up in the room you want to heat.

If you want better quality advise, go to a heating specific site, such as heatinghelp.com

If you want less abuse[which will not be the case at a heating site] dial it back a notch and try to digest what people are telling you, whether you want to hear it or not.

 

[dirttracker18]

Seriously?
I asked for observations and experiences from people who have changed their heater and what I keep getting is advice on mine. That's great and I do read and consider what people say but some are speaking without a solid knowledge base and making statements they cannot back up. It is just unsubstainiated opinions and guesses about what I am doing and what I may or may not know.
Those that have chimed in and know what they are talking about have added some food for though as I consider attempting to optimize the system and thank you to those.

So to answer your question I DO want to hear useful and pertinent information that people have. I am ignoring information that is flawed or baseless.

I guess the post title is what is throwing people off. I really would like to hear some real world experiences from people. However I don't seem to be getting any takers.

I did not really want to go to other sites as we have many knowledgable people here and many have express that they have done just what I am asking about. In addition most sites don't treat newbies who show up and ask questions very well. In general, poeple on this board are must easier to deal with, even when debate begins.

Unless I actually get some stories on here, I may have to change my plan of attack. At this point I have decided not to buy the Hydroshark at this time. I want to wait until I have more information upon which to make an educated decision. I have a couple of other options available to consider including waiting to see government grants come back so we can move ahead with the plan for geothermal for the house. That would change the game once again.

 

[Possum]

The problems people have using tankless water heaters relates to their restriction of flow in order to raise temp. a tank does not restrict flow in this way.

The Hydro-hark is sold as a boiler. It is manufactured by Stiebel Eltron. They look identical to the Tempra Plus line of tankless water heaters, but are claimed to have different internals. They have 3/4 NPT connections but the internal plumbing is much smaller. See above quote.

For savings on heat - is your building sealed up and insulated as well as you can? Does your electric provider do low cost energy audits? Have you considered an real electric boiler? One with an outdoor reset that might provide some savings? Thermolec makes a 11KW mini boiler (BT-11tmb) with one - here it is for $935 http://www.blueridgecompany.com/radiant/hydronic/325/thermolec-boilers How about supplementing some of the demand with solar? Ever thought about moving someplace warmer....

 

[dirttracker18]

Well judging by the views, this thread is being watched by a number of people so I thought an update is in order.

First off, after speaking with the designers of my system they do believe there is the 'potential' for cost savings by using the on demand unit that I mentioned. Notice they said potential. They believe that there will be savings but but would not commit to any figures. Basically the likelyhood is that I would save some money on heating costs and they confirmed my logic as to the reasons why. However, the payback time may be lengthy, then again it may not be too bad. Long term yes.

For now I will stay with the current set up.

However, my electrician (a master electrician and has been involved with the instal and trouble shooting of many infloor systems) was hanging out at the shop today and I picked his brain as to the option of changing to an on demand boiler. He also sees the benefit but had a suggestion that should eleviate one of the issues with extreme cold temps.

To add to the story, I noticed the issue of running out of hot water when we had a two week cold snap. At one point I went into the shop and found I had lost about 3 degrees of temp. This was due to running out of hot water after having to have the service door open during the extreme cold. I had the race car trailer in the garage with the car loaded up for racing to keep it warm for the next days races and had the door open to back in, hook up and pull out. The system continuing to run after a big loss of warm air and cooling of the floor were to blame. The system ran out of hot water before the floor had recovered and air temp in the garage had risen. This meant the pump continued to circulated with only warm water. The tank could not reheat the water as it continued to circulate.

My electricain buddys suggestion to fix this was to simpl`y hook up a relay that would turn off the pump when the upper element turned on. Under normal operation the upper element will not turn on as the cool water enters at the bottom. We have checked this as he had earlier added indicator lights hooked to the elements so I could tell when elements were on and which ones. The only time the upper element comes on is if most of the hot water was used up.

Now if this happens in the future, when the upper element turns on, the relay will shut off the pump, stopping circulation and allowing the elements to reheat the water. If the temp is still down in the shop, when the element turns off, the pump will restart and have plenty of hot water to use.

Seems to be a simple idea that will eliminate the issue of running out of hot water. This was the major concern in the first place as when this happens both elements are on and the pump runs until I notice the problem and turn the thermostate down to allow the tank to reheat.

This should solve that issue and save some money as it will give the tank the chance to catch up to demand when it calls for more hot water then it provided at one time.

 

[danski0224]

I still fail to see how any savings will be attained, other than standby losses, which are negligible... unless you go high tech and match flow rates.

An 11kW unit has roughly 37,400 BTU available.

What are the ratings on your pump in GPM?

Supply and return temps?

What are the temperature rise ratings on that boiler in GPM?

In other words, if you have a 7 GPM circulator and desire a 120* outlet temperature and have 100* retun temp, will the boiler deliver that 20* rise at 7 GPM?

Of course, the return temperature would need to meet the boiler manufacturers' minimums. You may need additional piping and a mixing valve to do that.

You have to look at the boiler flow data and see if the boiler is rated for a 20* rise at whatever your circulator GPM is.

Taken a step further, if you have a "dumb" circulator and replace it with a variable speed circulator with supply and return sensors... the circulator will adjust GPM to meet demand.

Hopefully, the boiler you are looking at has low water cutoffs and flow sensors built-in. If not, you better add some. Of course, the flow sensors would have to work with the modulating circulator.

So, once you go through all this, and if that 11kW boiler is capable of meeting the heat loss of your garage, you will see additional savings because you are heating a much smaller volume of water with the storage tank out of the picture.

I am not capable of quantifying that number, but through logic, the savings are possible.

If that boiler has staged heating elements and an outdoor sensor and a controller (built-in or aftermarket), demand will be matched with outdoor temps.

Given you proposed solution above (the relay), I would try some other stuff first.

Primary-secondary piping will allow you to run a hotter water heater loop and a cooler in-floor loop. You need 2 circulators to do this. The natural hydraulic properties of water and proper piping will keep the 2 loops from mixing with a simple check valve. You will need a mixing valve on the floor side unless your boiler will work with low temperature water directly (some of the gas high efficiency boilers have built-in controls for this).

I would pipe in a mixing valve to the tank as-is. This will allow you to run the current tank at a hotter temperature if the thermostat allows it.

I would wire up the elements so they both come on at the same time.

You could try an outdoor reset control and wire in each element as a "stage" of heat.

If you are willing to install a relay to shut down the circulator when the upper element kicks on, then I would install a modulating circulator.

If the piping is reworked now, you may get much of the savings you are reaching for.

Once the piping is re-worked, the system will work with a future boiler.

Unless you have a primary-secondary loop now, or at least a mixing valve, simply plopping in an on-demand boiler will probably do little.

 

[stingry]

The system ran out of hot water before the floor had recovered and air temp in the garage had risen. This meant the pump continued to circulated with only warm water. The tank could not reheat the water as it continued to circulate.

There is your problem, your hot water heater does not have the capacity to keep up under extreme conditions! I do not know why some people want to overcomplicate these systems. There are many on this forum that run these systems on hot water heaters and on demand water heaters. You just do not have enough capacity when it gets really cold.

These are relatively simple systems. You just have to put in as much heat as is escaping your slab. For this reason, I do not think your "stop circulating until the water heater catches up" stategy will work. While the hwt is shut down, the slab continues to cool, adding to the load waiting for the system once the circulators turn on again. You will then again run out of hot water and the cycle starts all over again. I don't know much about electric hwt's. but rewiring the elements so that they both work in tandem as suggested in a previous post seems to make sense.

I would think that a properly sized on-demand unit would work just fine. It sounds like your system is working quite well, it just needs more heat input during extreme conditions.

Cheers
Steve

 

[danski0224]

The OP has never posted a calculated heat load.

Given the size of the space, and assuming an available 11kW of heat (~34,700 btu), I don't think it is enough... unless the space is exceptionally well constructed and insulated- especially the perimeter of the slab.

This is before considering that both elements are not on all the time, if I am reading correctly.

I did a heat loss on a 22' x 28' x 12' garage (one 16' door, one 8' door and a double man door- all insulated), and a water heater was just big enough with 2 x 6 walls and regular insulation. It also has 5 loops- none more than 300' of 5/8" tubing. It is warmer here in winter than the OP's location.

 

[dirttracker18]

Just to clarify, both elements are wired independent of each other and both controlled thermostatically at the element. In other words, yes they are wired so they can both come on but they only come on when called for. When the system is running the tank cools from the bottom up. This should be logical but has also been proven by the indicator lights we installed to let us know when an element is on. Under most conditions the upper element rarely comes on. The bottom element always comes on shortly after the pump starts. Having the upper element on when the water at the top of the tank is already up to the desired temp is not neccessary and would only waste electricity.

To answer stingry's concern, yes it will work. The floor does not cool fast enough to be concerned. When the system fell behind on demand for hot water, I simply turned the thermostate down below the current air temp until the hwt was fully hot again. During this time the air temp in the garage did not drop at all. When the tank was hot again I turned up the thermostate to 1 degree above current air temp and let the system get me there. Next day up another 1 degree, and over again until I got back up to where I wanted to be. The real problme comes when I don't notice this issue right away. Then the hwt is heating constanltly, and using lots of electricity, as it cannot get reheated while the water is circulating. Setting up to stop the pump when the tank runs out of water will just be doing the job for me when I don't immediately notice the problem. This may not even be an issue for the rest of the season as I think the coldest part of the year is behind us
This issue only happens when we get extreme cold (below -25 c during the day for more then a few days). Other then this the system has no problem keeping.

Danski, I already have a mixing value. I do not think you could run a HWT system without one. You would run out of hot water in no time like that. The shop is 2 X 6 construction with R 21 insulation and I spent a great deal of time making sure it was very well sealed as all of my heat loss calculations show that being excessive with sealing makes a bigger difference then the insulation itself. This has shown itself to be an issue when I attempt to use my exhaust fan in the winter as it cannot draw air very well with the doors shut. I once turned on my fan with the attice door open and it pulled all my batt insulation out of the hole. If someone opens the man door while my exhaust fan is running it is ripped out of their hand and the door slams open. I also have 2 inches of rigid insulation under and around the slab as well as extending out 4 feet all the way around to keep our extensive frost away from the slab. Blown in R 40 in the attic.

 

[arb905]

Dirttracker18,
These guys are bashing you like a readheaded stepchild. If you are using a water heater designed for a hot water system in a home, you will eventually create a balance in your heat temp, ie inlet and outlet will slowly close in on each other. Using a boiler will increase efficiency because you will not be mixing heated water with conditioned water. Water in may be 80*F and leaving water will be 110*. The pump will run when the t-stat needs heat and the boiler will come on only when the outlet temp drops below setpoint. You said you had propane. You might be better off switching to a 90+ propane boiler, and possibly a storage tank.

 

[stingry]

out of curiosity, how warm do you keep the water in the HWT? is it possible to turn up the water temp during the coldest days. Since you do have a mixing valve, this would give you a larger amount of stored heat to draw from. Just a thought.

Cheers
Steve

 

[billpa68]

what is pressure drop over or through a tankless water heater (44k btu input) OR WHERE CAN i FIND OUT?

 

[don38506]

I live in Winnipeg and have in floor heat in my garage. I run 4 loops in 750sq ft of slab. I used to have a 50 gal HWT that did the job for several years although I sometimes found (rarely) it worked to keep up when it was really cold out. The tank had 2 4.5kw alternating heat coils. Last year I switched to a 10kw electric boiler, heat on demand, from a company based in Minnesota and have been extremely happy with the decision. I have extra floor space. The heat bill dropped, but not by much. It was still worth it. Have not regretted the change at all.

 

[overdriv]

Dirttracker,

I have a very similar setup as you describe yours. Only I use a 40 Gallon NG water heater. I have the temp set to 130*F on the water heater. No mixing valve. When the weather is very cold, my system will run out of hot water also, but still maintains 90*F supply and 72-74*F return.

Room temp on thermostat is set at 60*F. Slab sensor is set to 58* and the top of the slab is 64*F give or take a few degree here and there.

I have yet to get a full months utillity bill, so I can't comment yet as to how much gas it is using.

The one thing I did to improve heat transfer to the slab was to slow the circulation of water. Also, I have spent some time trying to balance my 5 loops. These two things have allowed me to maintain about a 15-20* difference between my supply and return, regardless of the supply temp.

I to have wondered about a tankless water heater, but the initial cost is quite high. I wonder if one would ever experience a payback.

With all that said, I want to tell you I have a friend that uses an electric hot water heater. His runs out of hot water as yours does. He rigged up a couple of relays and timers that shut off the circulating pump after length of time he has determined it takes the water to drop to a certain degrees, shuts off the circ pump and lets the water heater catch up and after another length of time that it take for the water heater to catch up, then turns the circ pump on. That cycle continues till the thermostat is satisfied.

IT WORKS WELL for him. It ought to work for you. I can get the particulars from him if you want. Good luck and keep updating us on your progress.

 

[D.J.]

I'da swore Fastback asked you if you had the elements tied together and I thought you answered, yes? Then later on we find out they weren't tied together. Also can we know what is your calculated heat load?

 

[dirttracker18]

I'da swore Fastback asked you if you had the elements tied together and I thought you answered, yes? Then later on we find out they weren't tied together. Also can we know what is your calculated heat load?

Just to clarify that first question, both elements are wired independent in that they can come on at the same time. You cannot, or at least should not tie them together. Both have their own thermostatic switch although normally one will affect the other.

Now in my case they come on as needed and can both be on at the same time.

I will have to find the info for heat load calcs although I am not sure why people keep asking for info like that as all I asked for was real world experiences from people that switched from a HWT to an On Demand boiler.

I just want to hear from those people how it worked out for them.

As an update we did instal the relay that shuts off the pump when the tank runs out and it is working great. We did have an extremely cold day when I was in the shop and the pump was shut down when the upper element came on. About 20 mins later it came back on when the tank was hot again and was then able to maintain a higher temp into the floor.
In the past at the point the tank ran out of hot water the system would just run until I turn it off. This time it only ran for another 15 minutes to get the temp back up in the shop after having to open the service door for an extended period.

I would still like to find a better solution down the road (propane on demand unit perhaps as electricity is getting very expensive in Ontario) but this will work much better for now. I had hoped to go geo thermal for the house and garage but the provincial grant is being terminated at the end of this month so that plan will be on hold for now.