I have a 300 sq/ft garage that I am heating with in floor heating. The heating requirement is 10,000 BTU/h. I want to use the hot water heater from my house to pump water through a heat exchanger as a heat source. I have used google to find calculators for this purpose and found a few but I am not sure how to use them. I was wondering if anyone here knows hot calculate this or do I just get a 10,000 BTU/h or greater exchanger and size the pump accordingly to it's specs?
plated heat exchanger calculation
- Thread starter bandito
- Start date
Kaizen
Well-known member
You sure about that Btu need?
Is this pex in concrete? Insulated slab?
Once an insulated concrete slab is up to temp the btu required changes drastically.
Is the water heater electric? Do you have a boiler or air for the house?
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Is this pex in concrete? Insulated slab?
Once an insulated concrete slab is up to temp the btu required changes drastically.
Is the water heater electric? Do you have a boiler or air for the house?
Sent from my iPhone using Tapatalk
The Btu is correct. I have used many a calculator including design software specific for radiant heating. 10,000 Btu is the maximum required based on door/window sizes, spray foam insulation (R20 walls and R32 ceiling) etc. Slab is also insulated with r-10 rigid board underneath and on the sides. The foundation is also insulated to three feet below grade with r-10 rigid board on the inside. I got a pretty good envelope lol.
The water heater is gas which puts out 40,000 Btu. It supplies the house also but it's only me in the house so not a lot of hot water use anyway and its forced air the heat the house.
Jim greengo
Well-known member
Are you wanting to heat the garage with pex in the floor or forced air?
Couple thoughts, everything on the potable water side needs to be non- ferrous metal, this means a stainless or bronze circulator for the potable side.
Watch the ratings on the heat exchangers, many will be rated with input water hotter then you will have from.a domestic water heater.
The parts add up fast, two circulators, heat exchanger, pump relay, tempering valve, air elimination device of some sort. A Taco X block might be an option as it has all of that built in.
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Watch the ratings on the heat exchangers, many will be rated with input water hotter then you will have from.a domestic water heater.
The parts add up fast, two circulators, heat exchanger, pump relay, tempering valve, air elimination device of some sort. A Taco X block might be an option as it has all of that built in.
Sent from my SM-G965U using Tapatalk
I have the radiant side done already. I have pretty much what you have listed including a pressure relief valve and manifold.
The supply side I decided I will get just get an exchanger larger than 10,000 btu and a Delta t variable speed pump. This way I can increase the temp on my hot water side or the Delta t on the pump to get the results I need to heat my garage. The pump is about $300 usd online but my supplier will be less.
Thanks for your help.
That's why I was going to get the Delta t pump. I noticed looking at the specs of exchangers and for example to get 100,000 for a given exchanger you would need 10gpm at 180f. So I figure with temp gauges, Delta pump and adjusting the temp of the water heater I should be able to get the right btu for the radiant side.
Thanks again.
You may need a heat exchanger that's rated at 30 or 40k btus since you will have water considerably cooler then the 180 degrees that most of the ratings are based on, it's not real easy to find info from the manufacturer for a case like this sometimes.
FWIW we have a system like this at our shop, it uses a pair of taco 007 circulators(stainless for the potable side) and IIRC a 40k heat exchanger, it's doing more space but since the floor covering is wood the temp is limited.
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FWIW we have a system like this at our shop, it uses a pair of taco 007 circulators(stainless for the potable side) and IIRC a 40k heat exchanger, it's doing more space but since the floor covering is wood the temp is limited.
Sent from my SM-G965U using Tapatalk
fitter30
Well-known member
How many feet of pex and size are in the slab? By the time you buy a plate HX, bronze pump and valving to limit water temp on pex side it would cheaper to do it right. If the HX would develop a leak between systems you could poison someone.
2011laramie
Well-known member
This is in my house we built last year. Doesnt run the garage, but runs the floor. And heated house in Alberta during winter time construction with no issues. Hot water temp in tank is only 125F. Floor injection temp is around 90F.
I wouldnt worry about poisoning a system. Use proper food grade glycol, and besides floor systems are 12-15psi versus domestic water is probably 40-80psi.
I wouldnt worry about poisoning a system. Use proper food grade glycol, and besides floor systems are 12-15psi versus domestic water is probably 40-80psi.
