Green Points: Radiant Heat Floors

Radiant-floor heating has its origin in ancient Rome, where fires were built beneath the floors of villas. Early Korean buildings were similarly heated by channeling flue gases beneath floors before venting those gases up through chimneys. Frank Lloyd Wright piped hot water, rather than air, through the floors of many of his buildings in the 1930s—a practice that has become common in custom homes today.

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Just how do these systems function? Radiant flooring systems come in two different forms. Electric radiant flooring is comprised of resistance wire that circulates heat through the tile, while hydronic or hot water radiant flooring relies on polyethylene tubing to connect water to a home’s boiler or hot water heater and return it to the floor when needed.

While more economical, electric radiant flooring doesn’t have the same kind of popularity as hot water radiant flooring, which can approximately cost up to $15 per square foot to install.

Unlike forced air systems, radiant heating doesn’t cause harmful allergens or dust to come up into the air, allowing those with sensitive systems to rest both easily and warmly. The heating pad embedded in the subfloor allows warmth to be distributed evenly throughout the room, and as a result may help homeowners save on heating costs throughout the fall and winter months.

While many manufacturer’s warranties vary between 10 to 20 years, homeowners should be careful to inspect the fine print of these agreements, as they may reveal that the warranty covers the replacement of a heating mat yet excludes other parts and labor. A trusted professional can help decipher these issues and provide valuable advice about the product that may be best.

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Benefits of Radiant-Floor Heating

Radiant-floor heating offers a number of significant benefits:

Comfort. By far, the biggest selling point for radiant-floor heating is comfort. The large radiant surface means that most of the heat will be delivered by radiation—heating occupants directly—rather than by convection (the primary mechanism of heat delivery from conventional hydronic baseboard “radiators”). Warmer surfaces in a living space result in a higher mean radiant temperature, a measure of surface temperatures in a space that influences the rate of radiant heat loss from occupants). With higher mean radiant temperatures, most people are comfortable even at lower air temperatures. Delivery of the heat at floor level with a warm floor surface also allows occupants to walk around barefoot even in winter—a very popular feature. Enhanced comfort should be a big selling point in any green home, so a strong case can be made for this heating approach.

Energy savings. There is potential for saving energy with radiant-floor heating through several mechanisms, including lower thermostat settings, lower-temperature boiler settings, and reduced infiltration. Homeowners with radiant-floor heating are likely to be comfortable at lower air temperatures because of the elevated mean radiant temperature in such homes, the lack of significant airflow (as occurs with convective hydronic heating and forced-air heating systems), and the delivery of heat at floor level. Proponents of radiant-floor heating argue that someone normally comfortable at 72°F (22°C) will be comfortable in a building with radiant-floor heating kept at 68°F (20°C). If this is true, one would expect people with radiant-floor heating to keep their thermostats lower and thus realize significant energy savings.

Improved indoor air quality. An argument can be made for improved indoor air quality in houses with radiant-floor heat. Compared with a conventional forced-air distribution system, there is likely to be less dust circulated around the house. And unlike electric baseboard or forced-air heat, there will be no surfaces hot enough to burn dust particles—which could introduce volatile chemicals or toxic particulates into house air (even passing through filters)

When and Where Radiant-Floor Heating Makes Sense

It has been pointed out that radiant-floor heating systems may not be the best choice for extremely well-insulated, passive solar homes. So when do they make sense?

• In houses and small commercial buildings with conventional levels of insulation and standard insulated-glass windows—especially those in climates with minimal cooling loads—where the extra comfort of radiant heat is desired and the budget allows. • In buildings with large open spaces and tall ceilings.

• In buildings where air-flushing is common, such as garages, fire stations, airplane hangars, and industrial spaces (because the large-area radiant floor allows quick recovery).

• When cost is not an issue and satisfying most or all of the heating load with solar energy is a high priority.

• When building occupants have acute chemical sensitivity or allergies—in which case there may be concern that dust could be distributed through a forced-air system or that high surface temperatures from a gas burner or electric heating element will burn dust particles and cause health problems.

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With radiant floor systems, there’s no blower noise, wind chill is nonexistent, and you don’t have to mess with HVAC filters. The big benefit is that the heat is in the room — the floor and furniture — not just the air. You can adjust your thermostat to a lower temperature in a radiant house and achieve the same comfort level because the floor and furniture are where the heat is. Where you set the thermostat is a question of comfort, not numerical temperature.

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