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Small Radiant Loop

JohnCujie | Posted in Energy, Heating & Insulation on December 22, 2008 08:18am

My master bedroom/bath area is distinctly colder than the rest of the house. It’s kind of a separate wing, a bit of a bottleneck for air to flow back there. At least that is my theory. Same construction as the rest of the house. I have spent time plugging any air leaks and boosting insulation. House is heated by forced air, which we seldom use, just to take off the morning chill and once in a while during the day. EPA fireplace insert keeps the house warm.

I don’t want to disturb any finishes. Is it a crackpot idea to run a small underfloor radiant loop using the hot water heater as a source? Too expensive for the benefit? We only want to increase the heat about 3 degrees.

John

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Replies

  1. DanH | Dec 22, 2008 11:18pm | #1

    There are various forms of in-line duct fans you might want to consider, if you think the problem is simply a too-restricted forced air duct.

    The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
  2. flathead50 | Dec 23, 2008 01:43am | #2

    John,
    If you are not running the forced air fan when the wood heater is running then it will be cooler there in comparison to the rest of the house because there is no RADIANT effect from the wood heater (since that is line-of-sight). CONVECTION requires some sort of means to circulate naturally (warm to cold) or with force ( a fan). Why not just an oil-filled radiator plugged in through an appropriate amperage-rated timer? It'll come on when you need it without remembering to turn it on.

    Some folks run their "summer" fan on the air handler to circulate heat around the house when the wood heater is on. But the heat loss from any ducts in unheated space reduces the efficiency; and the while the air is room-temperature warm, it will feel cool to anyone near a diffuser and will be uncomfortable.

    Using a DHW tank as a space heater requires you run your potable water from the tank. Depending on the material you use for the distribution, it may not be suitable for potable water. Plus, you would probably need to temper the water in the floor to less than you would want for your DHW temp.. Add to that the stainless pump and control, and you have a pretty sizable investment in parts. What's labor cost?

    I'd go for the $79.95 radiant space heater.

  3. frenchy | Dec 23, 2008 01:54am | #3

    Yes it will work if you have a pump to drive the hot water thru the system..

    1. RobWes | Dec 23, 2008 03:59am | #4

      Just don't forget about the other items related to RFH including the fact that it is not instant.

      May I suggest an electric radiant ceiling or cove panel. It's very fast to heat and easy to install in most applications. 

      1. frenchy | Dec 23, 2008 04:15am | #5

         a pump would cycle hot water from the water heater to the floor of the bathroom and the flow rate could be manually adjusted (simple in-line valve to meet temp needs) 

          Thus it would solve the instant heat requirement. Plus eliminate all the rest of the gear..  I assume the floor is accessable or could be made accessable from below.. then simply staple up some Pex with aluminum under the area of the bathroom run the pex into the line from the water heater and return it back into the water heater.  all that would be needed is the pump and a simple valve to regulate flow to the desired temp..  If you want you could put a timer on the pump to shut it off when warm floors wouldn't be required.. or you could be elaborate and keep all the hot water lines constantly hot so you don't have to waste water getting hot water at places remote from the water heater..  

         Sure you could use electric heat or several other solutions but that's not what he asked about.   

        1. RobWes | Dec 23, 2008 04:56am | #7

          I realize that is not what he asked but only wanted to have him think about other ways to "skin a cat". At the end of the day the electric would most likely be an easier install and much less $$$ for most applications.

  4. USAnigel | Dec 23, 2008 04:25am | #6

    No its not a crackpot idea and a warm floor is really nice!

    Could be a few bucks to do. I'll bet two work time days plus materials equal about $1500.

    You could install a electric heated towel rack, or toekick heater. Do the job and cheaper to install. Either way about $350ish. 

  5. Clewless1 | Dec 23, 2008 04:36pm | #8

    Great idea. Not sure about using the hot water heater directly, though. Don't think it would meet code ... and for good reason. You don't want that potable water sitting in your floor all summer and then circulated back into your potable water system. I may be wrong, here, but I think codes don't like you doing that. Maybe someone can help, here.

    I did my radiant system w/ a water heater ... but mine has a heat exchanger inside the water heater. You can easily adjust supply water temps, etc. to meet your needs.

    Your concept is solid, simple; but implemementing it will require some additional thought. You can get yourself a heat exchanger, but then you have two pumps (one for the water heater side and one for the floor side ... albeit both will be quite small).

    Another option is a second water heater. Work out the details and it could serve you well.

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