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Radiant in Garage

Brian_57 Member Posts: 6
I have to give an estimate to heat a new 2 car garage that is being added on to a customers house. He's considering radiant as an option. The garage is 27' x 25' with a 10.5' ceiling, 2 9'x7' doors, 1 36" x 48" window, and a 36" side entry door. The slab is going to be 5" thick. I ran the slant fin heatloss and got about 21000btuh heat loss. I will be installing a new hot water boiler as well. If i get this it will be my first radiant job. what program do you use to figure the lengths, sizes, and number of loops? I would let the supply house figure it out but don't trust them as much as you guys. I have a the knowledge to hook everything up it's just the sizing i don't know. Any help, pointer, or pitfalls to avoid would be greatly appreciated.

Thanks a bunch

Northern Jersey


  • Darrell
    Darrell Member Posts: 303

    Keep it simple...675 square feet of floor...coverage at 12" centers...use two 300' runs of tubing. Start at the outside and work in, if the center of the floor gets a little wider no problem. I usually use 1/2" Wirsbo...it comes very convieniently in 300' lengths. At 1/2" x 300' you can run it all day long with a stock Taco 007. Keep both lengths the same and you don't have to worry about balancing them. Definitely insulate under slab, and at the perimeter. If freezing at the overhead doors might be an issue, and easy way around that is to circulate the floor continuosly and add heat to the floor with your choice of injection, four-way, etc. Don't overthink the project...you'll get it and probably never want to go back! The fun part of radiant is that the rough-in is done and you don't need to go back until time to set the boiler.

    Have fun!
  • Brian_57
    Brian_57 Member Posts: 6

    Thanks for the info hopefully he'll go for it.

  • hr
    hr Member Posts: 6,106
    How will the garage be used?

    If it is just car storage a design of 50 may be plenty. Often 15 or 18" tube spacing will get that job done. Actually a unit heater would be best for a seldom used storage facility :)

    If it will be a working shop they may desire a warmer design temperature, and nothing beats a warm slab for standing and working on.

    I would spend the MOST amount of dollars on the slab and building insulation if in fact it will be heated. That's a gift that keeps on giving.

    The slab edge is the biggest loss. Design a way to use 2" down to the footers. The front edge along the garage door is all but impossible to get a good insulation detail. If it will have a concrete apron you can hide some r value there.

    Don't be fooled by the miracle 1/2 high r products under slab insulation products!

    hot rod

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  • do everything what

    Do everything what Hot rod said as he took the words right out of my mouth....
    INSULATE, INSULATE ! I've seen jobs that boiler won't shut off due to lacks of insulation because the builder told customer it wasn't required by codes. While other jobs where water heater was used and only ran once or twice a day due to everything and everywhere was insulated!
    Good luck...
  • Ron Gillen
    Ron Gillen Member Posts: 124
    Radiant Tube Heater

    With the ceiling height you have, another option, if it's not going to be used as a shop is a direct vent radiant tube heater. I have a ten foot tube, 30,000 btu that hardly runs but when I need it will warm up the garage in half an hour.
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