Retrofit Radiant Heating

January 17, 2008

Radiant heating is an efficient and comfortable method for heating. Instead of heating air and blowing it into spaces to mix with the cooler air and increase the temperature, radiant heating directly heats everything around it. When you stand in direct sunlight and feel the heat on you, that is radiant heating. Household radiant heating uses hot water, either from a water heater or from a boiler, to convey heat throughout the house. Some older homes used hot water or steam and radiators, which provided both a direct radiant heating source in the room, as well as indirect heating of the air passing the radiator and circulating into the room by convection. Newer radiant systems turn the entire floor into a radiant heating surface, providing even radiant heat throughout the house.

For the past several months, I have been slowly installing the tubing for a radiant heating system in my own home. The process isn’t normally really that drawn out. However, since I’m doing the work myself, on available weekends, it’s a slower process than having a crew of professionals come in and do the installation in a couple of days. But, regardless of the time it takes, the installation method is fundamentally the same.

I am lucky in that I have a single story home, so accessing the underside of all floors was relatively easy. Retrofitting radiant heat into a multi-story home would require either removing the ceiling on the level below or fastening the tubing to the existing flooring and then raising the floor level by a couple inches with an overlay of concrete or tile grout. While this can be done, it is a much more involved and expensive process.

Radiant heating is a green choice for heating for a number of reasons. For people with allergies, getting heat without blowing air around through dusty ducts is highly preferable. Water is also much denser than air, so it is more effective a medium for heat transfer. The typical human thermal comfort profile also tends toward having more heat at the extremities (namely the feet) while having slightly cooler temperatures for the head. This very much matches the heating provided by an in-floor system. Warm floors are also very comfortable for smaller children who like to play on the floor. And often, a radiant heating system can be set a little bit cooler than a forced air system because the direct heating from the radiant system is comfortable, even if the actual room air temperature is a little bit cooler (again, think of being in the direct sun on a bright, cool autumn day).

The next step in the process is going to be having the plumbing connected, with a heat-exchanger to transfer heat from our water heater (which was oversized in order to be able to run this system while still providing us hot water in the house) along with the other pipes and valves and bits of equipment necessary to make the system work.

In our installation, we are going to keep our forced air furnace in place for now, in case we get some really cold days that the system isn’t able to keep up with. But the sizing of the system seems to be large enough that we shouldn’t have any troubles with it. We’re all looking forward to having the radiant system up and running in the next couple of weeks.

You can see the PEX tubing (white) fastened to the side of the joist with clips (black) spaced every couple of feet in the photo. The cross pieces shown are left from removing the old ceiling that was in one part of the basement. They turned out to be very handy to help support the tubing in place until I could get the clips hammered into place, but they are not a required part of the system.

An article from ‘This Old House offers more information and discusses the advantages and the process of installing a radiant heating system, as well.