Radiant Floor Heating Newbie

Old 07-22-06, 08:28 PM
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Wink Radiant Floor Heating Newbie

Hello all, I am currently remodeling a space of about 9' x 20' in my basement. I have broken up the existing concrete slab and I am considering replacing my baseboard heating with a radiant loop. I cut out my baseboard heating units so basically I have an open area with incoming and outgoing 3/4 lines. I figure since I have it all open here 's my chance. Can anyone tell me where I should start and what components I might need.

I can tell you that I have a HB Smith G200 cast iron boiler that is gas fired and it feeds about 40 feet of baseboard heating in the second floor. The unit also fed the 20 feet in the basement in which I am looking to replace. Any help will be greatly appreciated.

Old 07-23-06, 06:48 AM
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locknutt, welcome to the DIY Forums.
I moved your post here for the best answer(s) since it is actually more Heating than Plumbing. Good luck with your project.
Old 07-26-06, 01:51 PM
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I've hesitated in replying in the hopes that someone else would take the lead.

I think that you have opened a big can of worms with this project. Radiant floor heating CAN be a great way of heating a space but it really needs to be designed that way from the get-go, retro-fit jobs are rarely anywhere near as good as an original installation.

You will need to insulate your floor from the ground beneath. Although the common idea is that heat rises that is a misperception. Radiant transfer of heat travels in ALL directions and is fastest to the place of lowest temperature, in your case that will be the ground below your slab.

Water in the ground, either from a high water table or migrating surface water, may be another difficulty.

I would suggest that you excavate to a point where you can lay a bed of sand no less than six inches deep, a six-mil polyethylene vapor barrier with the seams overlapped 12 inchees and securely taped with foil tape and large enough to allow it to extend above the finished floor level. Then place a layer of 2 inch EXTRUDED (not beadboard) rigid foam insulation with a second layer of foil-faced 2 inch polyisocyanurate run at right angles to the first layer. Tape all of the seams with foil tape. Lay about an inch of fine sand over this to protect the insulation and then proceed to install the re-enforcing steel mesh and PEX tubing. Cover using a lightweight aggregate concrete to the finished floor height. Your outside walls need to be thermally insulated from the floor slab.

You will need to make some major changes in the piping from the boiler and include a temperature regulating valve to allow the floor system to run much lower temperature water through it. Most masonry radiant floors run 80 to 100 degrees in the water loop.

If you have any idea of using anything over this concrete floor other than outdoor/indoor carpet then I would suggest that rather than installing the PEX tubing in the concrete that instead you use something like warmboard and install the PEX just under the finished floor.
Old 07-26-06, 05:38 PM
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There is a lot to be learned about the concept and execution of hydronic radiant heat such as you propose. There is help here:http://************/zc9rj I installed radiant heat in the floor of my workshop. It was simple to do and works great. The key is in the design and layout.

Hope this helps.

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