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Old 12-14-2010, 05:24 PM   #1
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Can I use existing hot water tank for radiant floor?


I'd like to install some radiant flooring at some point, using pex. I'm wondering if there are any issues if I tap into my main water heater? From my understanding, this is not permitted, but just want to confirm. What I'd do is T off the hot and cold line, and basically force the water back into the tank through the cold line. Since I'm not changing the volume of water, I don't think I'd be forcing against the municipal water pressure that is feeding the tank.

One issue I can see is that my water would not be hot enough, and if I raise the temp to compensate, then it would be dangerously hot when the radiant floor pump is not running. I could deal with that though, just need to be more careful at the faucet.

If this cannot be done then my alternate plan is to get a tankless water heater in the future, use that for my hot water, and then use the existing tank for radiant floor only. OR just get an electric heater for the radiant. Would that be ok?

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Old 12-14-2010, 05:37 PM   #2
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Can I use existing hot water tank for radiant floor?


I would use an electric tank for the radiant and put it on its own loop. They make small 12 or 20 gallon space saver models for offices/warehouses which would be ideal for you. Not sure how fast they can recover but a small even flow may work good with them.

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Old 12-14-2010, 06:15 PM   #3
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Can I use existing hot water tank for radiant floor?


Was thinking one of those small ones too. They have some 3kw ones at Canadian Tire. I'd set the pump on a timer and play with the timing for best comfort at the times I'm home, so it would probably not be all that costly to run.
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Old 12-14-2010, 06:22 PM   #4
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Can I use existing hot water tank for radiant floor?


Get a nice Grundfoss or Taco cartridge type circ pump as the better ones have a 3 speed dial switch on the side of the pump and they are totally silent and work very well.
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Last edited by yuri; 12-14-2010 at 06:25 PM.
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Old 12-14-2010, 07:31 PM   #5
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Can I use existing hot water tank for radiant floor?


You will need a couple of things not typically needed with a water heater---

A backflow preventer- pressure regulator,expansion tank and the pump and thermostat--

I've only set up one of these and that was about 15 years ago---A hydronic supply house will engineer this for you----

I think Beenthere could tell you off the top of his head--He has great hands on knowledge of hot
water heating systems.
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