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Radiant Heat – Current Details for Wood Framed Floor Systems

Radiant heat is so popular in today’s new homes that it’s being used in a majority of the new homes we build. Over the last 5 years I’ve seen an industry that changed details about as often as the seasons change here in New England. However, I’m happy to say that the industry seems to have narrowed the design and construction of radiant heat for wood sub-floors into a fairly standard approach.

Standard Below Sub-Floor Approach

When we first started installing radiant heat in new homes there were so many different approaches that your head would start spinning out of control. Five years ago when I built my new home the plumber used a special rubber hose instead of the industry standard PEX that’s used today. All of the changing approaches were not surprising considering the use of radiant was fairly new to the industry here in the US.

I’m happy to say that the constant change in approaches is no longer happening. Today a vast majority of new homes heated with radiant are now built similar to the photo above. First aluminum heat transfer plates are attached to the bottom of the wood sub-floor. Next PEX tubing (#1 above)  is snapped into special tracks on the heat transfer plates (#2 above).

A close up of a typical heat transfer plate is shown in the adjacent photo. Shown here is the Uponor Wirsbo Joist Trak Heat Transfer Panel. The plates serve a couple functions. First of all they help transfer heat to the wood sub-floor more evenly and reduce the likelihood of hot spots. Secondly they hold the PEX tubing in constant contact with the sub-floor (this is something that was hard to achieve with the older stapling methods). Lastly they help protect the PEX tubing from any small nails or screws that might be fastened down into the sub-floor (albeit little protection if you drive long screws or large framing nails!).

Radiant Heat – Insulation for Wood Sub-Floor Installations

The other aspect of radiant heat for wood sub-floors that seemed up in the air for years was how to best insulate it. Again it seems as though the industry has finally settled in on an approach.

Today when we install radiant heat below a wood sub-floor we use foil faced fiberglass with the foil facing up towards the heat tubes. In the adjacent photo you can see the pink fiberglass insulation installed in the joist bays.  The foil is facing up to help reflect heat back up towards the sub-floor.

The other important factor that you can’t really see is the position of the insulation. The insulation shown at right is installed in a 12″ deep joist bay. The insulation is only about 6″ thick (R19 approx.) which leaves an air space above it between the foil facing and the bottom of the sub-floor.

Be Sure Your Radiant Heat Is Installed Properly

We’ve been successfully using this approach for several years and it works amazingly well. If you’re thinking about using radiant heat in your home be sure to inquire with your heating installer about this approach. Be sure that you find out if they are using heat transfer plates, many will skip this in order to keep pricing down but I do not recommend it.

Also be sure you ask about the insulation and how the entire system works as a unit. If you follow these simple methods your new radiant system will work very well and give you and your family a great heating source.