I’ve heard a lot about radiant heat floors, but how do radiant heat walls and ceilings work?
Radiant heat floors, or “hydronic radiant floors,” have been popular for most of the 21st century as a very energy efficient way to heat a home. Radiant heat creates a more even floor-to-ceiling temperature profile than other heating systems, translating into cooler air temperatures higher up, which reduces the rate of heat loss through the ceiling. The lower water temperature needed for in-floor heat also allows the boiler to run more efficiently.
Radiant floors have tubing installed in a looping pattern and typically set into concrete or gypsum. Radiant walls and ceilings work the same way, except the installation is “dry,” meaning tubes are set into notches cut into insulation or plywood, or held in place with specially designed plates screwed onto existing walls or ceilings.
These systems are based on the law of physics that says “heat goes to cold.” Whereas hot air rises, radiant heat travels as waves in all directions and heats the objects it strikes.
There are several advantages to installing the system in a wall or ceiling. Because you are not heating a whole mass of concrete or gypsum (the standard floor installation), the wall or ceiling system can increase the room temperature more quickly. Whereas it may take two or three hours for a room to change five degrees using the higher-mass floor system, the response time in a wall or ceiling can be half that or less.
Radiant walls and ceilings are also less constrained by temperature. Because you have to walk on a radiant floor, you don’t want the surface to exceed 85°F. Walls and ceilings, on the other hand, can run at higher temperatures without burning your feet. (Note that this will cause an accompanying increase in boiler temperature and expense.)
Walls and ceilings are also easier to retrofit than floors. If you can increase the wall or ceiling thickness, you can add radiant heat fairly easily. With extra insulation, you can even add this system to the inside of an exterior wall.
When adding radiant surfaces to your home, it’s best to set up a system where you can control each room individually. Because radiant heat takes longer to react than other heating systems, you may want to be able to keep your bedroom, living room, kitchen and bathroom set at different temperatures.