Green Warmth: Radiant Floor Heating

Green Architect

Imagine a type of warm that is uniform, invisible, silent and energy efficient. No dust, no loud furnace and gushes of air, no odd high pitched squeal or clanking from a radiator &mdash just quiet, comfortable heat at your feet. Radiant floor heating offers a great efficient alternative to other mechanical systems, and rather than heating the air, it only heats you.

Ever notice how on a cold day standing in the light of the sun feels so much warmer, even though the temperature is the same on a cloudy day? Radiant heat works like that!

Types of Radiant Floor Heating
Hydronic: The most common type of radiant floor heating, hydronic systems use in-floor PEX tubing to distribute hot water; the floor slowly heats up and radiates heat into the room and warms objects in the room rather than just the air. Radiant tubes can be installed in a number of ways, the most common methods are: embed within concrete slabs and lightweight concrete topping (which is poured on wood floor structures); attached to the underside of the subfloor with aluminum fins; on top of the subfloor in grooved panels; or within the subfloor structure (Warm Board). Each has it's own benefit &mdash the concrete acts as a thermal mass to retain heat and has low conductivity, so that heat is dispersed slowly and evenly throughout the day. Wood has a very high conductivity and very little thermal mass to store the heat, and requires reflective insulation or panels under the tubes to direct the heat upward. The concrete and WarmBoard systems are best for new homes, whereas the under the subfloor systems are the best way to retrofit radiant flooring.
Electric: Electric radiant heating is a much simpler system than hydronic &mdash all it is, is an electric wire mesh mat that is laid under your finish floor. It is very easy to install, however it is not a particularly efficient or cost effective measure. It is best to be used as supplemental heat to warm up a small area of cold floor &mdash bath and mudrooms are the best areas to utilize this system.
Materials: Once either system is in place, essetially any type of finished floor can be used. Tile is best because of it's ability to conduct heat, wood flooring can also be used as well as area rugs. It's best to avoid carpet because of the thick padded that's typically installed, which will act as an insulator and made it more difficult for the heat to conduct through the floor.

Benefits
Efficiency: Rather than burning air to create heat, radiant flooring heats bodies directly and can operate at lower temperatures than forced air heating. And unlike forced air heat, where the hot air rises and the cold air falls, radiant heat is always near the floor, which is where you need it the most.
Zoned Heating: The system can be zoned for each room, allowing the user to adjust the temperature accordingly.
Invisible: Because it's under the floor, the system won't interfere with furniture or wall layout &mdash no registers or radiators or baseboard radiators to contend with.
Air Quality: Radiant heat is preferred, particularly for those with allergies, because the air has more moisture, and unlike forced air heating, radiant heating doesn't require air to be blown around, which creates dust.
Solar Connections: When tied into a solar thermal system, radiant floor heating is even more efficient. Solar thermal panels can be used not only for domestic hot water heating, but also to assist in boiler heating. Using solar and radiant floor heating is a great combination of green systems.
Silent: The heating system doesn't make a sound, unlike typical radiators and loud furnaces.

Cons
Cost: Radiant floor systems and the equipment (boilers, pumps, manifolds, etc.) to run them are much more expensive than forced air systems &mdash you should expect to spend between $10-15k per floor of radiant heat, whereas a forced-air system can be installed for less than $5000.
Quanity of Mechanical Systems: If you live in a four-seasons climate where both heating and cooling systems are needed, than a forced air cooling system (ducts, blower and a/c condenser) will be needed in addition to the radiant, whereas forced air has both heating and cooling in one system. You may also need an additional system to balance humidity, which could otherwise be integrated into forced air systems.
Less Effective in Retrofit Applications: When retrofitting radiant heat the most common method is to essentially staple the tubes underneath the subfloor, with either aluminum fins or foil faced batt insulation below to reflect the heat upwards. This method is less efficient because the heat needs to travel through the subfloor and finished floor before it reaches your feet. If radiant heating is retrofitted over slab on grade, the concern is if there is no insulation under the slab, then the system will not only be heating the interior, but also the ground below.
Overboard: There is an argument that radiant floor heating is overkill and unnecessary for tightly built, efficient and/or passive solar homes. The efficiency of the home will make the efficiency of radiant floor heating less significant and payback of the system will take much longer. Passive solar homes will already be utilizing stored heat in the floor and walls of the building, which can throw off the radiant system.

Does anyone have any experience with radiant floor heat? Let us know in the comments!

Related:
&bull Extreme DIY: Radiant Floor Heating
&bull The Scoop on Radiant Floor Heat
&bull Radiant Heating for Kitchen or Bathroom Floor?
&bull Floor Panel Radiant Heat

(Images: 1&3: WarmBoard; 2:North American Tile; 4: Flickr member iLoveButter licensed for use under Creative Commons; 5: This Old House)