Monday, November 09, 2009
Keep your toes toasty with radiant heating in floors
By Ann Robinson and Annie Schwemmer
There are few things worse in the winter than stepping on a cold tile floor.
A heated floor is one of those luxuries that is becoming more common with the push for energy efficiency and better indoor air quality.
Radiant heating is a more efficient option compared to electric baseboard or forced-air gas heating. The lack of moving air also lowers dust levels in the house, which is good for people with allergies or anyone who loathes dusting.
Radiant heating systems involve supplying heat directly to the floor or to panels in the wall or ceiling of a house. The systems depend largely on radiant heat transfer. Radiant heating is when you can feel the warmth of a hot stovetop element from across the room. When radiant heating is located in the floor, it is often called radiant floor heating or simply floor heating.
There are three types of radiant floor heat: radiant air floors (air is the heat-carrying medium); electric radiant floors; and hot water (hydronic) radiant floors.
All three can be subdivided by the type of installation: Those that make use of the large thermal mass of a concrete slab floor or lightweight concrete over a wooden subfloor (these are called "wet installations"), and those in which the installer "sandwiches" the radiant floor tubing between two layers of plywood or attaches the tubing under the finished floor or subfloor ("dry installations").
Air-heated radiant floors: You don't see air-heated radiant floors in homes very often because air cannot hold large amounts of heat. Sometimes these are combined with solar air heating systems, but in cold climates they lose energy efficiency because they need a conventional furnace to pump warm air through the floors at night.
Electric radiant floors: Electric radiant floors typically consist of electric cables built into the floor. Systems that feature mats of electrically conductive plastic are also available, and they are mounted onto the subfloor below a floor covering, such as tile.
Because of the relatively high cost of electricity, electric radiant floors are usually only cost-effective if they include a significant thermal mass, such as a thick concrete floor, and your electric utility company offers time-of-use rates. Time-of-use rates allow you to "charge" the concrete floor with heat during off-peak hours (approximately 9 p.m.-6 a.m.). If the floor's thermal mass is large enough, the heat stored in it will keep the house comfortable for eight to 10 hours. This works best when daytime temperatures are significantly warmer than nighttime temperatures.
Electric radiant floors may also make sense for additions onto homes for which it would be impractical to extend the heating system into the addition. However, homeowners should examine other options, such as mini-split heat pumps, which operate more efficiently and have the advantage of also providing cooling.
Hydronic radiant floors: Hydronic (liquid) systems are the most popular and cost-effective radiant heating systems for heating-dominated climates.
Hydronic radiant floor systems pump heated water from a boiler through tubing laid in a pattern underneath the floor. In some systems, the temperature in each room is controlled by regulating the flow of hot water through each tubing loop. This is done by a system of zoning valves or pumps and thermostats.
The cost of installing a hydronic radiant floor includes purchasing a boiler, which will take the place of your gas-fired furnace. Residential boilers average around $5,000, with whole-house systems often running from $20,000 to $25,000.
Ceramic tile is the most common and effective floor covering for radiant floor heating, but you can also use vinyl, linoleum, carpeting or wood. But remember, any floor covering that helps to insulate the floor from the room will decrease the effectiveness of the heating system.
Though the initial cost of a radiant floor heating system is significantly higher than a conventional furnace, once you have enjoyed this type of clean, quiet, constant heat it will be difficult to return to the noise, dust and temperature swings created by a traditional furnace.
Also, just imagine: no more cold toes on that midnight trip to the bathroom. As always, we welcome your home architect design questions at firstname.lastname@example.org.