Hot water heaters for radiant heating

[MR P BODY]

Any of you use a hot water heater for your radiant heat source, I have been
looking at boilers but they are outrageous on price
Thanks for any help

 

[quatroad]

Buderus and Viessmann are a fortune (and nobody local had any long-term installation/service experience). We also looked at Munchkin and Lochinvar. Went with the Lochinvar Knight modulating condensing unit. HTH.

 

[GSSFC]

Don't use a hot water heater. I had one in my shop...it was a waste. The problem is that the first cycle of water goes out at say 120* but goes through cold concrete (and even when the floor is warm, it still comes back cool). The water heaters don't have enough balls to heat the 2nd and subsequent cycles of water back to 120*. So you have to heat FOREVER to get the performance and results out of the heating system you desire. What you save initially you will waste in fuel, and you won't be happy with it! You can have my hot water heater if you want!

Tim

 

[skeletonizer]

I know of two shops that use water heaters. One is just a 28 x 26 and the other is much bigger. They are both in Northern MI where it gets cold. They both have never complained to me about them.

They both heat all winter one with propane .

As has been said in other threads you have to heat all the time because of the huge amount of thermal mass in the concrete. It would take forever to heat a 10 degree shop and floor up with a water heater. The key is to never let it get cold and make sure you are well insulated and keep the damn doors shut.

My plan is a water heater and to set the stat for 50 and leave it there all year. I don't want my shop to ever get below freezing. I would have built a pole barn with barrel stove in it if I had planned on only heating it part time.

 

[A_Pmech]

AO Smith Vertex 50-gallon heater. It serves both my radiant heating load, and my domestic hot water. It's basically a commercial forced-flame heater in a domestic package. 100,000BTU, 98% efficiency.

 

[GSSFC]

I know of two shops that use water heaters. One is just a 28 x 26 and the other is much bigger. They are both in Northern MI where it gets cold. They both have never complained to me about them.

They both heat all winter one with propane .

As has been said in other threads you have to heat all the time because of the huge amount of thermal mass in the concrete. It would take forever to heat a 10 degree shop and floor up with a water heater. The key is to never let it get cold and make sure you are well insulated and keep the damn doors shut.

My plan is a water heater and to set the stat for 50 and leave it there all year. I don't want my shop to ever get below freezing. I would have built a pole barn with barrel stove in it if I had planned on only heating it part time.

Perhaps they are just accustomed to the usage and have nothing to compare to! A hot water heater is just not designed for constant use like a boiler would. A boiler has the capacity to reheat the returning water to the desired temperature prior to going back out into the system. Now an on demand hot water heater...maybe...don't know. I know I wouldn't put another system in with a hot water heater as the source.

Tim

 

[nate379]

I use a Burnham boiler and it's tied into my water heater. Water heater is just a tank that boiler water flows through. (indirect heated)

 

[tdkkart]

My shop has a Siesco on-demand electric water heater, works just fine, as did the tank type heater before that. It's not cheap to run but I really have no other choice.
If I had the ability to use Natural gas a tank type gas heater would work just fine, there are thousands of installations using tank type and on-demand heaters with good results.

As has already been said, radiant floor heating is a set it and forget it situation, which includes starting the heating system in the fall as the temp of the slab starts to fall below the design temp. If you wait until the system has to play catch-up you're gonna be disappointed.

 

[jeff5295]

I had this same question when I did my first radiant system. A boiler was going to run close to $2000 and the NG water heater was around $350 (several years ago). Nothing special, just Menards mid-grade model. I figured it was worth a shot to try the water heater as I would only be out a few hundred. It worked great. I had a 42x45 Morton building with about 12' ceiling. I kept the shop around 58-60 all winter. If you were wanting to be much warmer than that, then maybe the water heater wouldn't keep up. I found this to be a pretty comfortable temp to work in, as it feels a lot warmer with the radiant heat. We have pretty cold winters and the system seemed to barely run at all. I set the thermostat on the water heater to it's lowest setting and it was pretty cheap to operate.

I haven't bought a heater for my new shop yet and will investigate an on-demand unit. More money than a water heater, but we plan to stay at this location for a long time so I figure it may be worth the investment. Otherwise I would just use another ordianary water heater.

 

[chevelle64]

I'm using a 30 gallon, natural gas water heater. Radiantec recommended a water heater for my application, 840 sq. ft. The system hardly runs, and I love it!

 

[GSSFC]

FOr those guys that have hot water heater fuel by LP. What kind of fuel consumption do you see...daily, weekly, seasonal whatever? Also include the size slab you are heating. I consider them to be terrible inefficient based on fuel consumption. I do however believe they will get the job done, as I adequately heated the shop one winter with the water heater. But at a cost of nearly 40 gallons of propane a week at a cost of then $3+ per gallon. Unacceptable in my book!

Tim

 

[mmg440]

FOr those guys that have hot water heater fuel by LP. What kind of fuel consumption do you see...daily, weekly, seasonal whatever? Also include the size slab you are heating. I consider them to be terrible inefficient based on fuel consumption. I do however believe they will get the job done, as I adequately heated the shop one winter with the water heater. But at a cost of nearly 40 gallons of propane a week at a cost of then $3+ per gallon. Unacceptable in my book!

Tim

That does seem like alot! What size building and how is it insulated?? Does it have insulated doors, walls. It may or may not be the propane if the buling is also inefficient.

 

[jeff5295]

My previous shop had NG and was very cheap to heat with a 50 gallon water heater(roughly $60-$70/month over the house heating bill of the prior winter). The pump rarely turned on. I actually questioned if it was working a few times, but the heat was consistant. At my new place we have LP and haven't yet purchased a water heater but will need to before winter. The old slab was 42x45 about 5"-6" thick with 2" foam board under and around perimeter. New one is 36x56, same thickness and insulation under and around slab. New shop has spray foam insulation on walls and roof so I'm anticipating even better results.

 

[HoosierBuddy]

One thing I would point out is not all gas water heaters are created equally. While electric water heaters all have pretty much the same elements in them regardless of size, gas water heaters come in different BTU inputs. The BTU input is going to be the important thing for heating. The tank size has nothing to do with it, at least directly.


So...when I considered a gas water heater to run the hydronic system in my garage, BTU input was one of the main factors I considered. Then, after researching it more, I decided to go with a boiler. For me the way I justified the added expense was:

1. The boiler is 92% efficient which is much higher than a standard gas water heater.

2. A tankless boiler has no standby losses. I know you can get tankless water heaters too...but there again, they are more money than a standard tanked water heater.

3. A modulating boiler, like the one I have, can meet demand changes easily. I can change the thermostat and the system responds even in the dead of winter.

So...in the end my boiler was about 2 to 3% of my total project cost. If the heat doesn't work right...the whole project wouldn't be very satisfying. I should point out that I have a large bonus room on my garage which is attached and we use it every single day, so the heat up there is pretty critical (Zone 2). The boiler also supplies heat to the breezeway that attaches the garage to the house (Zone 3).

I'm glad I went the boiler route.

Phil

 

[Mungo Park]

I am building a 16X22 foot garage. I have the pex tubes in and was thinking I would use the water heater tank. My question is how long does a tank last before it needs replacing, ( I know depends on how much you use it) just a ball park, 2 years, 3,4... Does the tankless types like seisco tankless unit last any longer?

Cheers Ron.

 

[chevelle64]

I've only had mine running for about 6 months, 30 gallon natural gas, I have no idea how long it'll last. Hopefully about 50 years

 

[unimog1300]

I use a tankless water heater. The book says it's 87% efficient. I thought it was along the lines of 90+. BTU output is 15,000 to 180,000. Below is the post I wrote before. I've added 2 pix. HTH Steve


I use a Rinnai tankless also. Morton Building, 30 X 60 with 16' ceiling, fully insulated, and steel interior. Three garage doors 12 X 14, 10 X 8, and 8 X 8, walk door and two windows. Six zones in the floor, 2" foam insulated footings and 1" 4 X 8 foam on the perimeter only under the slab. I keep the building 50-52 starting Oct/Nov until............still turned on. Also I live in central Illinois. My propane bill is included with my wife's shop that is 22 X 28 and it is stick built, 2 x 6 walls and 2 x 12 ceilings, two story, one two car garage door. Our propane bills have been in the $1200 range for the entire heating season.....total for the two. She runs hers 65 plus for her comfort. The tank less in my building does an excellent job. I would definitely do it again the same way.


I forgot to mention the propane for my building also runs a standby generator that runs once a week for 15 minutes, unless of course it has to run.

 

[Mungo Park]

I should add I live in Winnipeg Manitoba, I have 3" insulation under the pad and will put doen insulation around the pad, 2' down and 2' out. I do not have the building yet.

 

[kvom]

I use a 7500W electric tank water heater; works just fine on my 25x36 slab, but we have a milder climate here.

 

[autoxbrian]

I have an 1800 sq ft attached garage, approx 11' ceilings, 2x6 walls w/ R21 insulation, R40 ceiling and R8 under the slab... was given wrong information at the time I put in the system and tried to run that off of an 80 gallon water heater.. (commence laughing)...

Moved to a Hydro-Shark II 20Kw modulating electro-boiler. This thing not only kept up, but it would cycle at maybe 1-2 hrs every couple days set to 58, in a colder-than-average Ohio winter. Went from close to $650 electric bills (whole house electric, geo-thermal heat) to $350 electric for the whole house.

 

[Jeepskate]

Wow...that's scary!! I'm researching now and live in Mid-Ohio too just across the reservoir from Mid-Ohio Sports Car Course. I'm all electric as well (just switched back off of my standby generator a few minutes ago due to a power outage) and the fear of a monster electric bill concerns me. I have a heat pump and 15KW aux heat strip with about $250/mo bills on the budget plan on a 2800+ sq ft house w/attached garage. I'll be adding a 32x40x14 clear-span steel outbuilding w/R11 on the walls & roof...considering using 'The Barrier' under the slab as it looks like the Dow blue board will run me more $$. Thinking about picking up a used 30 or 40 gallon tank heater to get me through this coming heating season (pushing the budget limits getting the building) and seeing how that goes then moving up/out to a Siesco next year when I have the funds if the water heater doesn't work out.

 

[autoxbrian]

I would strongly urge you to reconsider... Better leaving it cold for a year than trying to make a conventional water heater do the work... Gladly explain my findings in the same climate to you... Shoot me a PM with your phone #.

 

[B&H]

I just replaced the concrete floor in my auto repair shop and installed a radiant floor heat system.

After a short discussion with the heating contractor, it became apparent that a high-quality, high efficiency boiler was a no-brainer vs a hot water heater. We went with a Buderus with an outdoor reset/sunload sensor.

The increased efficiency will pay for the boiler in about 10 years at today's energy prices, so most likely less than that as energy prices rise. The cost of the boiler and install was 7K, and I will get about half of that back with current incentives in our area and tax breaks.

 

[autoxbrian]

Tried an 80 gallon water tank in hopes it would be able to recover at a slow flow rate (about 2.8gpm at the time).... it wasn't even close, the system ran 24/7 for a month (yes I cried at the electric bill...) and the garage barely stayed in mid/low 50s.

Here is the updated setup... 19.2 KW HydroShark II unit, good price, good warranty, and oversized for my application (Heat loss called for approx 50k BTU, and this unit is capable around 70k BTU) Ended up with a new pump that helped out considerably as well.

 

[Jeepskate]

Thanks again, Brian, for the links, photos, info, and taking the time to talk to me over the phone. I did a bunch more research last night and stayed up until about 1 AM playing with LoopCAD. What got refreshed in my memory last night is that I had seen it mentioned almost in passing in a couple of places that tank water heaters were okay for radiant *ONLY* if they're gas-fired...electric tank heaters simply aren't up to the task (as you found out the hard way). I did some heat loss calcs and it looks like one of the lower BTU Hydro-Shark II's will do the job for me...should be able to keep that cost to around $500...I can sell a few extra Jeep parts to cover that I stumbled across this site which others might find useful: http://www.radiantdesigninstitute.com/

It looks like Taco has a 3-speed pump now that's supposed to be roughly equivalent to the lower-end Grundfos. Which Grundfos model are you running? And what's that green unit between your expansion tank and the pump? My PEX, manifolds & test kit arrived today.

 

[autoxbrian]

You are welcome, glad to help out someone in the area, lord knows we are at a lack of any local knowledgable folks on the radiant side. The site you mentioned isn't bad, however do be aware that the writer stated multiple places that the information is ala 1996, so 13 years have gone by, and I am sure technology has improved/changed especially in this field.

Which unit are you looking at if I can ask?

My Grundfos pump is the 15-58, and is still less money, and can pump faster @ the same head loss from what I can see on the Taco 00R data sheet. I would honestly recommend that pump over the Taco, after owning both.

That Green unit is a Taco Vortech Air Eliminator, phenominal in works, though not very cost efficient. http://www.pexsupply.com/Vortech-Air-Separators-454000 But I know the system is air free, and it has maintained pressure since all the air was purged last winter.

 

[Jeepskate]

You are welcome, glad to help out someone in the area, lord knows we are at a lack of any local knowledgable folks on the radiant side. The site you mentioned isn't bad, however do be aware that the writer stated multiple places that the information is ala 1996, so 13 years have gone by, and I am sure technology has improved/changed especially in this field.

Some of the info looks like it was updated, like he mentions the 300 foot PEX limit being based upon the boiler tech available at the time and a couple of the 'snake oil' slab insulation products that are on the market now. Just adding it to my growing collection of links and absorbing the info. I'll definitely keep the age in mind.

Which unit are you looking at if I can ask?

The SH2-07 should do the job but I may go with the SH2-10 to allow for a margin of error and the eventual addition of some windows (doing this build on a tight budget, so I opted out of windows and will add them as I can afford to).

My Grundfos pump is the 15-58, and is still less money, and can pump faster @ the same head loss from what I can see on the Taco 00R data sheet. I would honestly recommend that pump over the Taco, after owning both.

Thanks for the recommendation. I was leaning toward the Grundfos but was curious about the Taco. I'm one of those 'do it once, do it right' kinda guys and hate to find out after I buy something that there was a better option. Drives my wife crazy sometimes...

That Green unit is a Taco Vortech Air Eliminator, phenominal in works, though not very cost efficient. http://www.pexsupply.com/Vortech-Air-Separators-454000 But I know the system is air free, and it has maintained pressure since all the air was purged last winter.

Cool...interesting piece.

 

[autoxbrian]

I'm in the same mindset, do it once and right, I just was given bad information re: water heater at the time.

For the $10 difference and buying a 40 vs 50 amp breaker... that is a no brainer to go to the 9-10Kw unit vs a 7Kw unit. I am surprised your heat loss numbers only came out to 20-30k BTU and not higher...

Glad to help out how I can, when you get past ground breaking, and to the time to lay down the insulation, grid and pex, let me know I would gladly lend a hand if you'd like.

This is a similar tool that I mentioned to you to cut the EPS like butter... this one folds like a pocket knife, mine doesn't. But the blade shape looks almost identical, easy to push into the board, and pull.

 

[tdkkart]

This is a similar tool that I mentioned to you to cut the EPS like butter... this one folds like a pocket knife, mine doesn't. But the blade shape looks almost identical, easy to push into the board, and pull.

The Dow-Corning 2" pink foam board I bought comes scored on 16 and 24" centers, makes it very easy to snap to size, otherwise a quick score with a utility knife is enough to make it snap off easily.

My system was installed by the previous owner with an electric 40 gallon water heater. Once it was at operating temp the system worked fine, only falling behind when I tried to make a change in temp.
I switched to a Siesco(HydroShark) heater in the hopes that it would be more efficient. Daily operating costs in the dead of winter did not change, other than possibly a small gain from the drop in standby losses. What did change was the system's ability to do a change in temp efficiently. The Siesco unit is able to keep up with the heating demand and can change the temp more quickly/efficiently.

There are ALOT of systems out there running on garden variety water heaters, some of them work, some of them don't, but of those that don't the problems have more to do with the design of the rest of the system than the heat source.
A BTU is a BTU, makes no difference where it comes from, the trick is making and delivering them correctly, while letting as few sneak out as possible along the way.

 

[Jeepskate]

I think a lot of it has to do with the temp of the returning water and how much water is sitting out in the PEX (I know it's circulating, just trying to simplify the concept). If you have 40 gallons in the tank and 60 gallons sitting out in the PEX with a significant temp drop in that return, the tank heater is going to have to work harder since it's trying to keep basically a continuous supply of 'too cold' water at the set temp (especially if it doesn't have a high enough BTU output) in order to try to keep up than the converse (60 in the tank, 40 in the PEX). The electric tank heater is probably fine for a smaller, heavily insulated space with small/limited windows & doors. In Brian's case, he has a pretty large space with lots of doors and windows. I'm probably right on the border. For the somewhat moderate price difference, the smaller footprint, and decreased likelihood of the unit not being able to keep up, the Hydro Shark/Siesco makes the most sense to me. If I could go gas, I'd probably be more likely to try the tank heater.

 

[Jeepskate]

Mine should work out such that I only need to cut a couple of sheets for insulating the sides of the slab. At 32x40 the 4x8 sheets fall right into place. Home Depot has the 2" pink, I didn't see the 2" blue listed at Lowe's...I may pop in there after work this evening for a look see and swing by Menards as well to see what they have and pick up one of those knives. One of my buddies had one like yours that he was using as a box cutter...don't think he realized what it was actually for.

You're right...I hadn't looked at the price difference...$10 is a no-brainer and I already have the breakers (bought a NOS lot of 5 from 20-60 A off Ebay for $15). The heat loss numbers surprised me too. I'll probably run a couple more calcs just to make myself feel more confident. I just might take you up on your offer. Moved out here from IL just about a year ago and don't really know anybody, so I usually work on my own or twist my wife's arm if I absolutely need another pair of hands.

 

[Possum]

So is there a difference between the blue and the pink foam other than brand?

 

[FXR]

I am going with a small hot water heater when I add on another 30x 15. I am going to do a bunch of small zones so the water in the lines does not have time to get all of the heat pulled out of it, this should reduce recovery time.

 

[Burl]

If you have 40 gallons in the tank and 60 gallons sitting out in the PEX with a significant temp drop in that return, the tank heater is going to have to work harder since it's trying to keep basically a continuous supply of 'too cold' water at the set temp (especially if it doesn't have a high enough BTU output) in order to try to keep up than the converse (60 in the tank, 40 in the PEX).

No way are you going to have a large amount of fluid in the pex. I have 1,000feet of 1/2" diameter pex in my slab and it calculates out to 7 gallons total.

 

[nate379]

To cut the foam a reg utility/drywall knife works just fine. Or you can use a sawzall for cuts to get the foam to fit around something.

The stuff I use is R-Tech Insulfoam. Seems to be very common around here.

 

[autoxbrian]

Hey Jeep-

Didn't get any notices of other posts on here, sorry I've been slacking (I got a new toy in the garage, and been working a ton both at actual work, and house work).

Here is a link to the board I bought at Lowes, seemed similar price to the other 2 (Home Depot and Menards (which wasn't there at the time), but the commonly found 10% off at Lowes made it a no brainer for me, since I bought and had delivered all the foamboard, wire remesh, tape, etc.


My system has approximately 24 gallons in the PEX at all times, mind you it is 3/4" and well over 1200 linear feet. Here's a chart to do the simple math (tells you how many gallons per 100 ft, so for 1000' of 1/2" PEX would be 9.2 gallons) PEX Volume Chart about half-way down that page.

My 80 gallon electric wouldn't keep up, but if you do the BTU output math... really electric water tanks only have a single element running at any given time, so never more then 4500-5500W, vs. the 19KW+ that the system thrives on now! Yes I have insulated overhead doors x 4, double pane, low-E windows x 5, and a walk in steel insulated door, but the insulative value in the ceiling R40, and walls R21 is much higher than most folks stand alone buildings.

I was born and raised in this area, but would be glad to lend a hand, and get to know some other quality folks in the area. Again, keep me posted and would be glad to help, at least it isn't a long drive for me. I will try to keep an eye on the forum, but you have my email and are welcome to email/call if you want a quick response.

 

[Jeepskate]

Thanks Brian. I was just in Menards on Saturday and happened to stroll past the insulation area and spotted the pink board and made a quick detour. They have the hi-density stuff intended for radiant on sale for $21.94/sheet for 4'x8'x2" for another couple of weeks...just a tad cheaper than Lowe's w/the 10%, so I'll probably buy it while it's on sale. Got my plans Friday evening, so I'll get the permit ball rolling this week and my builder just called this morning to see if the plans came so that he can schedule getting started with the grading & footers to allow for curing. The PEX stuff is all tucked in the garage waiting for the big day. Much appreciated...I'll keep you updated.

 

[autoxbrian]

Sounds like a plan!

what did you do for grid/rebar/mesh? I don't recall if I shared with you what we did and how well it worked.

Once you get closer to a date, let me know as our weekends seem to come in spurts of filling up a bunch, then being free a few, then back busy again.

Congrats on the find at Menards, was it R8 or similar?

 

[Jeepskate]

Back to the drawing board. Found out that I have special zoning as residential rual on a 'flag' lot which requires me to be 75 feet from *all* lot lines, so I'm moving the building down to a clearing in front of and to the side of the house, spinning it, and moving the 16x12 door from the endwall to the sidewall next to the 9x7 which I'm upsizing to a 9x9. I have to re-do my tube layout now. Zoning permit is in hand and hopefully I'll have the building permit this week and break ground next week. The builder is planning to use mesh. I figured I'd lay the insulation (R8 if I recall) and staple the PEX to it so that I can get out of his way and get the concrete poured without worrying about the guys tripping over the PEX.

 

[Dragster Racer]

I am perplexed about where the difference in heating cost comes from with the different water heating options. With comparing electric to electric, all are 100% efficient, so where would the cost/BTU difference come from? When comparing tank/tankless/boiler..again, where does the difference in cost/BTU come from? I understand efficiencies and standby losses with tanks, although if the tank is in the heated area, shouldn't that also heat the area, and not really be a loss at all?
Now, one thing that I understand for sure is the difference in performance with changes in temp. I think it goes without saying that you need to plan ahead with radient and be patient. If you want quick recovery, this is the wrong type of heating for the application.