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Radiant Floor Heating 101
Radiant floor heating, popular in new construction, has become a viable retrofit option.
The growing popularity of PEX (cross-linked polyethylene) tubing during the past 15 to 20 years has made radiant floors easier to install and leak-free. This was not so with ‘50s- and ‘60s-vintage radiant systems that relied on copper tubing embedded in concrete. With time, the tubing leaked and the systems were abandoned. Early on, PEX was not without hiccups as well. Tiny amounts of oxygen are able to penetrate the PEX lining, causing corrosion to metal components, such as cast iron boilers. Newer versions of PEX include an oxygen barrier.
More recently, installations were further simplified with the advent of subflooring that’s pre-fitted with tubing channels. Warmboard, for example, manufactures 4 x 8 radiant floor panels for new construction and 2 x 4 panels for remodeling that are lined with aluminum sheeting for even heat distribution. The panels are more expensive than materials used in some other systems, but they are more efficient and reduce the labor costs, too.
The growing popularity of solar heating has also caused builders and homeowners to give radiant floor heat a second look. Solar energy is a good heat source for radiant floors because solar thermal collectors are very efficient at supplying the lower water temperatures that such systems require.
The only negative for radiant floor heating is that it’s not so easy to use for cooling. With a conventional forced-air heating system, the same ducts that deliver hot air through ducts from the furnace can be used to introduce cool air from a central air conditioner. While radiant cooling is possible, it’s typically not cost effective to install. A chiller or geothermal heat pump must be used to supply the cold water. In addition, the tubing for radiant cooling is best run in the ceiling (not the floor, the better location for heating). And while radiant cooling systems will reduce air temperature, dehumidification may also be needed to make occupants feel cool.
COSTS OF RADIANT FLOOR SYSTEMS
For new construction, a hydronic radiant floor system is likely to cost more than forced hot air (ducts and registers) or hydronic systems (baseboard radiators). In the long run, however, it will save money due to lower thermostat settings and higher efficiency. The cost of retrofitting hydronic radiant flooring varies depending upon whether there is access to the subfloor and the extent to which flooring and ceilings must be torn out and reinstalled. As a starting point, materials and mechanical equipment for installing hydronic radiant heat in a 2000 sq. ft. home cost about $3,500 or $1.75 per sq. ft., according to the Radiant Floor Company. This excludes the heat source and assumes two zones (a 1000 sq. ft. basement and 1000 sq. ft. first floor). Labor costs vary by the job and location.
Electric radiant floor heating costs about $6 per sq. ft. for materials but is often less expensive to install because of lower labor costs. Unfortunately, it’s far more costly to operate and therefore generally makes sense as a supplemental, not primary, heat source.
IS RADIANT HEAT RIGHT FOR YOU?
Radiant floor heating, a no-brainer if you’re building a new house, can be retrofitted to existing homes, although installation costs will be higher. In retrofits, tubing is attached to the underside of the first-floor subfloor, assuming there is access to it from a basement or crawl space. If the renovation is extensive and the finished floor is going to be replaced in any case, it’s usually better to install tubing over the subfloor where it will be more efficient, easier to install, and require less tubing. Adding radiant heat to second and third levels, when existing floors are to remain in place, may require removing the ceiling of the rooms below to gain access to the underside of the subfloor.
Your heat source will also factor into your decision. If you have an efficient boiler that’s not too old, it probably can be used to supply heat to your radiant floors. If your boiler has seen better days, choose a high-efficiency, condensing, gas-modulating boiler that is capable of heating your domestic hot water, too.
To learn more about installation methods, check out this Radiant Floor Heating: How it Works slideshow.