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radiant heat in attached garage

mallen
mallen Member Posts: 7
Built a new home 2 years ago.

General Contractor installed 1/2" Oponor AquaPex, part number 1060500 (non oxygen barrier) pex in concrete

1,300 square feet

3 loops of 300' (actually I don't know for sure what length the loops are, I found an empty box so all I know is the tubing came in 300' rolls)

The 3 loops return to the basement

SlantFin heat loss calculation: 37,442 btu/hr (thanks for the advice)



I have an A.O.Smith natural gas hot water heater (HWH) that has outlets on the side for radiant heat, etc., and is used for the hot water in the house. I would like to create a loop with a heat exchanger and a separate stainless steel circulator to transfer heat to the radiant system. Will the HWH water be hot enough? I would like to keep the garage around 60 degrees using a slab sensor.

Then on the other side of the heat exchanger, using a pressure relief valve, air separator and a potable expansion tank (close to the circulator) and allowing plenty of "straight" piping (figuring at least 5") on each side of the circ, can I use 3/4" pex to go from the circ to the manifold? And maybe from the heat exchanger to the drain/fill valve?

Sizing the circulators is so confusing! I tried using the formulas I found, but came up with some goofy numbers! I found someones system that sounded close and used their information. Their head loss was 9 in the tubing and added 2 for the 90's, tubing, etc. That seems high to me, but what do I know?

Thank you, in advance, for your advice and help! I've been a lurker for a while on this site, and there's a lot of good information.

Comments

  • jumper
    jumper Member Posts: 1,827
    probably not

    I presume the heat exchanger will have circulators on both sides? All just to heat a garage?
  • mallen
    mallen Member Posts: 7
    correct

    a circulator on both sides of the heat exchanger
  • mallen
    mallen Member Posts: 7
    and yes

    all just to heat the attached garage
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,221
    The good folks

    at Taco have exactly what you need for your application. http://www.taco-hvac.com/uploads/FileLibrary/X-Pump-Block.pdf



    Harvey
  • mallen
    mallen Member Posts: 7
    Wow,

    you're right, perfect, expensive, but perfect!
  • mallen
    mallen Member Posts: 7
    If I'm reading the instructions right

    the system requires an air separator, expansion tank and pressure relief valve on both the supply and return lines on the X-Pump Block side of the system?
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,221
    Let's call

    the water heater side "primary" and the radiant side "secondary".

    You need the expansion tank, PRV (fill valve), air separator on the secondary side return line.



    For the primary side.

    If you have city water your water heater should already have an expansion tank. If it doesn't put one on. If you have well water, you will already have an expansion tank in place.

    Also install these on the primary supply and return. http://www.webstonevalves.com/default.aspx?page=customer&file=customer/wecoin/customerpages/balldrain.htm

    That will allow you to clean the mineral deposits from the primary side of the heat exchanger.



    Another thing. What make and model is this water heater? Some work for these applications and some don't.



    Harvey
  • mallen
    mallen Member Posts: 7
    A O Smith nat gas water heater

    Brand is A O Smith

    Model is GPHE 50 series 100
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,221
    You should not

    have a problem with that model.

    Run a good outdoor reset curve on the Radiant to minimize short-cycling the water heater.



    Harvey
  • kcopp
    kcopp Member Posts: 3,985
    FWIW...

    it may be much simpler and give you less headaches to just install a separate water heater just to do the radiant. no need for HX and extra circ pumps. May be less money and your hot water supply will not be compromised.
  • jumper
    jumper Member Posts: 1,827
    kiss

    I strongly agree with kcopp. Simpler,cheaper. You'll probably operate the heater at coolest setting. With recirculated water the heater will probably last longer than the house. Plus you save pressure drop through exchanger.
  • mallen
    mallen Member Posts: 7
    I hear what you're saying,

    but I was hoping to avoid that situation. I do have natural gas in the basement, but all my appliances are high efficiency and vented through PVC.

    How much compromise would I experience using the HX? I ignorantly assumed that once the slab would get up to temperature, it wouldn't be much of a compromise.

    I looked online at electric boilers that would produce 40K btu/hr, but they're almost as much as the HX.

    This upgrade may get tabled for a while. I just wanted a little more comfort in my garage.