Underfloor radiant heat is ideal for homeowners who want to take advantage of the clean, uniform heat of a radiant heat system, but without the added cost and labor of replacing all floors.
Underfloor radiant heating systems are installed under the existing subfloor between the floor joists. This type of installation is not as responsive as the aluminum base method, but it responds better than the thermal mass method.
The radiant heat under the floor needs to warm the wood subfloor and the floor covering above so it can radiate heat into your home. This makes it the most discreet radiant heat to install in an existing home. It won’t add any extra floor height or disrupt your existing floor coverings.
There are a few common underfloor installation methods: stapling with heat transfer plates, stapling without heat transfer plates, and hanging pipe in the joist space. This is how they differ.
Stapling with heat transfer plates
These systems use thin aluminum heat transfer plates that are stapled with radiant heat pipes under the subfloor. The plates are highly conductive and provide a large surface area that will absorb heat more quickly and keep you warm for much longer. Using heat transfer plates will distribute heat more evenly throughout the floor than other underfloor methods.
Most manufacturers make heat transfer plates to accept different pipe sizes. So you need to match the width of your heat transfer plates to the size of your pipe. Heat transfer plates also vary between 5 and 12 inches in width, depending on which brand you choose.
You want to get the best possible dish topping. If you use narrow plates, then you need to put two rows between each floor beam. By spacing the lengths of tubing about 8 ″ apart, you’ll get a much more even heating pattern upstairs.
Check each heat transfer plate before inserting it into the tube. Be careful of the sharp edges of the transfer plates as they could cut or damage the tube. Installation is easy, just wrap the plate around the pipe and attach it to the bottom of the subfloor.
If you are installing a 12 ″ wide plate, you will usually find pre-made slots for two tubes. Just make sure each heat transfer plate is stapled in the center of the floor joists. When stapling plates, staple towards the outer edges of the plate, as well as one row of staples towards the center.
By attaching the staples to the outer edges of the boards, you allow the pipe to move away from the subfloor and will help prevent noise caused by the expansion and contraction of the pipe.
Stapling without transfer plates
When giving up the heat transfer location, be sure to use the proper staples to hold the tube in place. You don’t want the pipe to come in direct contact with the subfloor; otherwise the pipe will make noise as it expands, contracts, and rubs against the subfloor.