— Anita, Brooklyn, New York
A: Richard Trethewey replies: Nowadays there are products designed to retrofit a radiant heating system into almost any wood frame structure. If the floor joists are open from below, tubing can be looped in each joist bay. Tubing should be held in place with aluminum transfer plates or transfer "traks." These transfer plates increase heat transfer and lower water temperature. If you're in a cold climate and want heat, don't avoid them.
Always use PEX tubing. PEX stands for cross-linked polyethelene, an incredibly tough plastic that can be heated and cooled a couple of million times and not become brittle. Avoid rubber tubing. Remember you need a steady supply of warm water in the tubing under the wood floor, not shots of hot water that could damage or cup the floors. Always use a mixing valve to send consistent temperature to the floors.