I am building an addition on my existing 2 car garage, and I will be putting radiant heat in the floor of the new part. The total size will be 1440 square feet, with the addition being 792 square feet. I am hoping to be able to heat the entire garage with just the radiant heat in the floor of the addition part. I have called and talked to several radiant heat experts, but I am getting all different answers. I have been told that there is no way its going to work, I have been told to put 1440 feet of tubing in the floor so it will be enough to cover the entire square footage size. Another place said just to use 1/2" PEX with 12" spacing (the normal) and it should do ok. Somewhere else said I should use 5/8" or 3/4" tubing spaced 8-10". I know that there are some very knowledgeable people here, so I would like to get some input on your thoughts. The garage will be very well insulated, it has 2 regular size garage doors and 2 walk through doors, no windows. The floor will be 8" thick with 2" styrofoam underneath it. The foundation on the addition part has 1 1/2" styrofoam on both the inside and the outside. The ceiling height in the garage will be 12 feet. The coldest temperature in the winter is usually doesn't go much below 0. I know that the close to the floor in the old part of the garage will always be on the cool side, but I am hoping to be able to keep the air temp in the entire garage around 60 degrees all winter long. Any advice would be greatly appreciated!
PEX sizing and spacing advice needed for unusual situation
- Thread starter 1233user
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stingry
Well-known member
I have a friend who built a 40x70x14 pole building. It is well insulated and sheetrocked. He only put PEX in one-half of the floor, intending to partition off the heated from the unheated side. The partition was not necessary, heats the entire building with a 40 gallon water heater with only 1/2 the floor being heated. I don't know why this would not work for you.
Cheers
Steve
BadgerBoilerMN
Well-known member
The sure way to know is to pay a designer to do a proper heat load, which should include a CAD drawing, specifying tube size, length, spacing and output during design conditions.
Or, you can guess-by-golly.
Or, you can guess-by-golly.
Highbeam
Well-known member
No advantage except less head loss when you're pumping. Stick with the standard, 1/2" pex, 12" spacing, 300 foot max, even length loops.
BadgerBoilerMN
Well-known member
Highbeam has the standard formula...he loves it. But it doesn't account for the load presented by the old, unheated space. May cover it fine depending on the load, heat source and design temperature.
Highbeam
Well-known member
I love the standard formula as much as you love telling people to go and get an analysis done. For pipe layout just follow the standard, for sizing your heat source accurately, you need a heat load calculation.
Ok, I downloaded LoopCad, and filled out all the information to get a heat loss summery. On the bottom Room 1 is the addition that will have the radiant heat, and Room 2 is the existing garage that will not have radiant heat. I attached the pdf file, hopefully you can read it. Any final thoughts before I go ahead and order the tubing? Right now I am planning on four loops spaced at 10" using either 1/2" or 5/8" Wirsbo HePex tubing. Thanks!
2005UltraClassic
Member
I recommend that you install, 3 each loops at 1/2" X 300'. Your spacing will be at 10". This will work out to be very close to 300 ' per loop ( actually 305 feet per loop, but you can fudge that amount with no problems). Because you have 3 loops, you will need a 3 port manifold. Radiant heating systmes work best because of the mass of the slab. Having an 8" thick slab is an advantage as it provides mass.
I would make sure that the slab is insulated on all 4 sides with a minimum of 1/2" insulation board. Make sure that the slab is isolated from any footings or outside walls. You must isolate the new slab from the original slab with insulation foam board or you will have a heat leak from the new slab to the old slab and that will cause the system to run for as long as it takes for the thermostat to be satisfied by the the heat radiating off the slab. (I have seen cases where the installer did not install a barrier and then wondered why the electric bill was so great.) You shold install at a minimum 2" below the concrete slab. I do not see any advantage for using 5/8" PEX.
Typical heat loss for new construciton and for a garage is 15 BTU/square feet. This means that to satisfy a heat loss of 15 BTU/Square Feet. Your slab is you will require a heater of approx. 3.47 kW. I would suggest that your heater be a 7kW heater. I would suggest that your pump be a Grundfos UP-15-42. A good product to use for this application is the "Radiant Made Simple" RMS-7. This heater requires a 40 amp circuit breaker. It provides 23,890 BTU output. It is a easy to install. This kit is designed for the DIY individual. This pump has no problem pumping up to 5 each 1/2" X 300' loops and you will have only 3. This product is designed for the DIY individual. It is compatable with 1/2" PEX. You can find this radiant heat kit on the internet.
The radiant heat from the new slab will heat the area above the old slab by convection. It will be cooler in the area of the old slab. The slab will not be warm as is the new slab. You might chose to install a fan to move the warm air to the area of the old slab.
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Thank you very much for the reply! I do have 1 1/2" styrofoam on the inside of the foundation walls that comes up to 2" below the finish height of the floor. I also have the same 1 1/2" styrofoam between the old floor and the new floor, it is also 2" below the finished surface. At the top of the styrofoam I cut a 45 degree angle so the concrete will taper off. So there will be 2" at the top of the floor where the concrete makes contact with the foundation and the original floor. There will be 2" thick foam under the entire new floor.
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