Radiant Heat Insulation for Subfloors
Keep the Heat Up

Using radiant heat insulation is a great idea for any type of radiant floor heat. The type of insulation that you choose depends upon what type of radiant floor heat system you are installing. There are two types of insulation. The other insulation is used below a subfloor that has radiant heat. This article focuses on insulating a subfloor. Two learn about the second type of application, visit this article which explains insulating below a concrete slab.

Insulation a subfloor is a relatively simple process. Once you have radiant heat placed into a subfloor, you fill the empty joist spaces with insulation. There are typically two ways PEX radiant tubing is installed into a subfloor. This will influence how you insulate the subfloor.

Radiant Heat Insulation for PEX Tubing Attached to the Bottom of the Subfloor

The aluminum plates and PEX tubing in the picture to the right are exposed. Insulation will cover this up to ensure the radiant heat energy goes up into the subfloor.

With a system like this, where some of the PEX tubing is exposed, you need to leave a small air space between the radiant water tubing and the insulation. One to two inches of space will suffice.

If you are able to cover the vast majority of the radiant tubing with aluminum flash plates, the insulation can be attached right up against the subfloor and aluminum plates.

One word of warning. Make sure you are careful when screwing in the aluminum plates to not damage the finished flooring above. Measure how thick the subfloor is so you don't have screws or nails poking above the finish flooring.

When you insulate your subfloor, choose insulation that has an R-Value of 19 or higher. In most systems, a foil backed insulation will be used to prevent the insulation material from getting to hot. The foil reflects the heat up into the subfloor and keeps it away from the insulation.

What the R-Value stands for is the level of "thermal resistance." A higher number means a better insulator. Usually a higher R-Value also means thicker insulation.

Radiant Heat Insulation for PEX Tubing in or above the Subfloor

There are now several systems where you can put an engineered subfloor with channels precut for PEX radiant heat tubing. With a system like this, the insulation that is below the subfloor doesn't come in direct contact with the PEX tubing or aluminum.

For a system like Warmboard, where the radiant tubing is in the subfloor, as well as a laminated aluminum layer, you don't need foil backed insulation. Standard fiberglass batts can be used in this situation. You still need to make sure the R-Value is R19 or above to ensure the radiant heat goes up instead of down.

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