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Radiant Patio?!?

Brad_8 Member Posts: 2
I've installed a new 8" concrete patio with 600' of 1/2" PEX tubing @ 6" oc. I tried using the house heater, an older 50 gal domestic water heater. You can imagine how well it didn't work. I'd like to replace the unit, keeping in mind some degree of economy, with either a tankless unit or a tank system that can service the patio and the 2 bath house. We're in California, and don't expect to use the patio system @ outside temps below 50 degrees F. Do I need to go to a boiler or is there a high-demand tank water heater or a tankless unit that will work?


  • Tom Meyer
    Tom Meyer Member Posts: 300
    Don't use the same water

    Are you using the same water source for both heating/conditioning as you do for your domestic potable hot water? If so, I hope you have a heat exchanger in there somewhere.

    Tom Meyer
    Senior Designer/Trainer
    Precision Hydronics Corp
  • Edmeister_2
    Edmeister_2 Member Posts: 4
    Radiant Patio


    From your description it is difficult to tell how you looped the tubing. With 600 ft of tubing I hope you used two circuits, as all manufacturers recommend no more than 330 feet or so MAXIMUM loop length per circuit due to tubing pressure losses. If you have one circuit of 600 ft length your pressure drops will be higher than normal, requiring a larger horsepower pump than normal. If your pump is too small your flow rate will suffer and the performance will be disappointing. You should look at your pumping power closely and get help in selecting the correctly sized pump. Not knowing the size of the patio, but assuming it is average size with not a great heat loss at the ambient temps you mentioned, a 50 gallon gas fired water heater should heat the patio slab. By all means use a heat exchanger for the slab loop if sharing the water heater with domestic water systems. Good luck.
  • Brad_8
    Brad_8 Member Posts: 2

    Thanks guys, for the info so far. To answer Ed's comment, I have (2) loops of 300' each. The pump is a Grundfos UP26.

    I plan on replacing the existing heater and would like to combine radiant with domestic. How do I incorporate a heat exchanger?
  • brent_3
    brent_3 Member Posts: 4

    I would be interested in knowing how well a radiant patio will work. I will guess not very well. As soon as the slightest breeze blows all your heat will blow away with it. Your money will also blow away. I'm assuming there are no walls.
    A high end restaurant asked us about installing a radiant slab for their new patio to extend the season. We advised against it.

    Did you figure out how many btu's it will take to raise the temp of your slab? You might be surprised.

  • let us know

    how well it works. i'm thinking of heating a screen house on my deck, i think it might work if it's not windy at all. bob

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  • Rudy
    Rudy Member Posts: 482
    Kind of reminds me....

    when I would leave door open and my Dad would yell "What are ya tryin' to do, heat the outside!" I'm not an engineer but it sounds like you guys are in snow melt territory. JMHO. Anybody heard of blue jeans and a sweater?

  • i'm way to cheap

    to pay to heat my deck. i hope to use excess solar energy in the summer months. sweaters and blue jeans work o.k. but radiant heat is awesome! bob

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  • Art Pittaway
    Art Pittaway Member Posts: 230
    If you want a dry deck,

    and a little heat it will work like a snow melt. It sounds like you have 300 sq.ft. X 100 btu/sq.ft. = 30,000 btuh input. That is a dedicated 40 gal water heater running full time to heat 8" of concrete to 80*F?...Don't expect it to respond fast (the more heat you put in the more leaves), and hold your breath when you get the gas bill! But, I know a contractor that put in a heated slab (about the same size) 4" thick, insulated and covered but open sides (gazebo), for his older dog that wasn't to bad to heat/melt and this is Northern Illinois. Take a close look at your goals and see if it is going to give you what you want, a canvas cover will reflect heat back to the patio and increase the effectiveness. Trial and error. Art
  • Roger Litman
    Roger Litman Member Posts: 64
    Heating a patio

    As I suspect that the patio only sees intermittent use, you may be better off with using one of the overhead propane or natural gas fired radiant heaters which work very well and can be turned on when you are using the patio. I know that you have put a lot of effort in laying the tubing, but throwing good money after bad makes little sense-

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