Hardwood + radiant heat — the spec guide most installers skip

Why radiant ruins floors

Hardwood wants 35–55% relative humidity. Radiant systems running over 80°F surface temp dry the wood from below — moisture content drops below 6% and the boards cup.

The five specs that prevent it

1. Engineered construction only. Solid hardwood expansion across the grain hits 3–4× engineered. Cupping is guaranteed within 18 months.

2. 5/8" thickness max. Thicker boards insulate the heat from the room — you get inefficient heating AND moisture damage. Most architectural-grade radiant specs call out 1/2" or 5/8".

3. Hard-wax oil or UV-acrylic finish. Aluminum-oxide UV finishes are fine too. Avoid polyurethane site-finish over radiant — the heat causes the topcoat to micro-crack.

4. Surface temp limit 80°F. Set the slab controller, not the room thermostat. Most modern systems support this.

5. Acclimation 7–10 days minimum. Boards delivered, opened in the install room, system running at projected temp for a week before laying.

The expensive mistake

Solid oak over radiant heat cups. Sand it flat and it cups again the next season. Engineered construction is what stays flat. Spec it right once.

Spec'ing a radiant project? Call (847) 233-6300 and ask.