The concept of radiant floor heating has been around for thousands of years — and it's easy to see why the idea has stuck around for so long. Ancient Romans constructed a layer of tile raised slightly from the subfloor, creating an airspace through which heated air could be circulated. Some modern radiant floor heating systems use air, although they improve on the Roman design by circulating it through pipes or ducts — but the most efficient systems use water. By efficient, we're talking energy savings of 30 percent over other heating systems, including forced air and electric heaters, according to Energy.gov.
Hydronic radiant floor heat is more comfortable than forced air heat because it's more uniform and doesn't pass through an air handler heat exchanger that robs it of humidity. When radiant heating elements are installed in the floor, the floor tends to be warmer than the ceiling, and in most houses, the floor is where people spend the bulk of their time. The improvement in comfort can be achieved while consuming less energy than is needed for most other heating systems because all you have to do is heat water and circulate it through a network of pipes. There are no blower or compressor motors to worry about, no heat loss through ductwork and, importantly, no extra allergens circulating through the air.
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The main issue for homeowners who are considering replacing their existing heating system with radiant heat is cost — because running a network of water pipes under the floor is no small operation. The best time to do it is during new construction, when pipes can be embedded in the floor before the floor covering goes on. Another good time to do it is during a major remodel that includes installation of new flooring. If neither is the case, there are DIY solutions that don't involve disturbing the flooring, but they aren't as efficient.
Radiant floor heating is more comfortable and efficient than forced-air heat, and the monthly operation costs are less, but the upfront costs of installing in-floor heat can be quite a bit higher than for a conventional HVAC system.
Components of a Radiant Floor Heating System
A radiant floor heating system needs a heat source, and in most cases, this is an electric or gas-fired boiler, which operates much like an on-demand water heater. In a closed-loop system, which is the most common, water is heated in the heat exchanger inside the boiler and circulated throughout the network of pipes made of PEX tubing, which is the best material for this application because of its flexibility and durability. A small circulation pump keeps the water moving, and the most recently developed pumps consume only 9 to 13 watts, which is about as much as an energy-efficient light bulb.
Hot water proceeds from the boiler to a manifold that splits the hydronic radiant floor heating system into zones. Each zone may have its own thermostat, which allows homeowners to selectively heat some parts of the house and not others, and that saves even more energy. After circulating through the pipe network, water returns to the boiler to be reheated.
A boiler isn't a prerequisite for a hydronic radiant heat system; the heat source can also be a conventional tank-style water heater, or water can be heated by a boiler and stored in the tank. In an open system, the tank is fitted with an inlet and outlet for the hydronic network in addition to the inlet and outlet for the home's hot water plumbing pipes, and the hot water is used both for water heating and room heat. In a closed system, a heat exchange loop for the radiant heat system is installed inside the water heater, and the fluid circulating in the heating system never comes in contact with the home's hot water. In this case, the fluid is typically a mixture of water and anti-freeze, which has better thermal properties than water alone.
Wet vs. Dry Installation Methods
Perhaps the best way to install the pipes for radiant heat systems is to embed them in fresh concrete, which is known as a wet installation. At ground level, the pipes can be installed in a slab foundation, and in upper stories, they can be installed in a layer of concrete or gypsum supported by a plywood subfloor. This installation method is used to best advantage when the floor is under construction, but it can also be used on existing floors, and it offers these advantages:
- Concrete (and gypsum) act as heat sinks and continue to radiate heat after the system switches off and water stops flowing.
- The pipes are protected by the solid material surrounding them, reducing the likelihood of leaks to almost zero.
- The heating system takes up no more space than the concrete or gypsum in which it's embedded.
When installing radiant floor heat on an existing floor, a dry installation is usually more practical, and it can be accomplished in more than one way. One of the most common is to remove the floor covering and subfloor, attach radiant insulation to the underside of the floor joists and snake the tubing through a series of holes drilled in the joists. Another method is to install furring strips, or sleepers, to the existing subfloor, run the tubing between them and install a second layer of plywood on top of the sleepers.
The dry installation method used by many installers uses 6- to 8-inch-wide planks. You attach them to the subfloor with just enough space between them to allow the tubing to fit, and the floor covering can be installed right on top of the planks. Because this method avoids the need for an extra layer of plywood, it doesn't raise the level of the floor as much — only by the thickness of the planks, which are slightly thicker than the diameter of the tubing. Most installers install aluminum heat transfer panels under the planks. They have a tubing-sized groove that fits in the gap between the planks, and they get nailed to the subfloor before you install the planks.
Radiant Floor Heat Is Luxurious
There's a reason the Romans, who reveled in luxurious living, created air-driven radiant floor heating systems for their homes. Heat naturally rises, so when it originates at floor level, it eventually fills the room, but until it does, the floor is the most comfortable part of the room, and that's where your slipper-clad feet are located. (Who doesn't like to stand on a comfortably warm surface when their tootsies are feeling the effects of a frosty morning?) Just as it does in the room, the heat rises up through your body, comfortably warming it inch by inch, which is an effect you won't feel with air heated by a heat pump or furnace.
Radiators and baseboard heaters are hydronic systems that work on the same principle as radiant floor heating, but the heat they emit is localized, and if you want to get warm quickly, you have to stand near one of them. Besides, they are separate fixtures that take up space in the room, and they don't heat the room as evenly, meaning that some pockets of the room are bound to remain colder than others. It's possible to install hot water tubing in radiant panels in the walls to save room space, but even they won't heat as uniformly as floor heat and are more of a localized solution than a whole-room one.
Radiant Heat Flooring Options
You can use radiant heat with virtually any floor covering, but some are better than others. The best ones are ceramic tile, vinyl planks, laminate flooring and exposed and painted concrete floors because they don't inhibit natural heat convection, and they don't have to be nailed down. You can also use carpeting provided it isn't too heavy, but nail-down hardwood floors are out unless you install the tubing under the floor joists, where it isn't as energy efficient. If you're dead set on hardwood and you install the heating system in the subfloor, you might consider either a floating engineered flooring product or one that you can glue down.
Is Radiant Heat Right for You?
Because radiant floor heat is a luxury, it comes with a commensurate price tag. Installation of a new in-floor radiant heating system can cost anywhere from $14,000 to $48,000, which is quite a bit more than a furnace ($4,500 to $9,000) or a heat pump ($2,500 to $10,000), and unlike a forced-air HVAC system, you can't use a radiant heat system for cooling. If you're remodeling a home that already has a hydronic radiator or baseboard heat system, however, the cost to convert it to in-floor radiant heat will be considerably reduced and might be more cost effective. In either case, once the system is up and running, it will cost less to operate than a forced-air system, but it will still take many years to recover the upfront installation costs if you ever do.
Dry installations cost on average about $10 per square foot, as opposed to wet installations, which cost around $14 per square foot, so it costs less to retrofit an existing room with radiant heat with pipes installed in the subfloor or under the joists than it does to install a whole new system in concrete. If you're on a budget, it may make sense to approach radiant heat installation on a room-by-room basis using in-floor heating to make the rooms you use most often more comfortable.
Hydronic Systems Are Energy Efficient
Once you get past the upfront costs for installation, you'll appreciate the energy savings of a radiant heat floor. Both radiant heat and forced-air systems use a gas or electric appliance, such as a boiler, a furnace or a heat pump, but there is minimal energy loss with a radiant heat system compared to a forced-air system, which loses 20 to 30 percent of the heat generated through the ductwork. Also, water in a hydronic system doesn't have to reach very high temperatures to keep you warm; 75 to 80 degrees Fahrenheit is usually sufficient. Add the fact that much of the heat generated by a floor heat system is absorbed by the flooring, which continues to radiate heat after the system has been switched off, and you have a potential energy savings of around 30 percent when you choose hydronic floor heat over a forced-air system.
Alternatives to Hydronic In-Floor Heat
Electric radiant floor heating isn't nearly as economical as hydronic heating in terms of monthly costs, but it's a whole lot less expensive to install. It may be the solution you're seeking if you want the luxury of in-floor heat, but you can't afford to install a hydronic system. Heating elements for electric systems can be installed in the subfloor or under the joists, and because you simply connect them to the home's electrical system, you don't need a boiler or manifold. You can even use heating mats to make rooms in your house that are especially cold more comfortable, which is a common practice in Japan, where central heating isn't as common as it is in North America.
Any time you use electricity as your heat source, you can expect higher energy bills, so electric radiant heat isn't a practical whole-house solution. However, it's good to remember that any room in which you install in-floor heating is bound to be more comfortable because radiant heat is simply more efficient at heating a room evenly without the cold air pockets created by forced-air systems. Whether you install electrical heating elements in the floor or go whole hog and install a hydronic floor heating system, you'll be more comfortable on cold days, and that in itself may be enough to offset the extra monetary output no matter whether you install it in one or more rooms or in the entire house.
- Grainger: Hydronic Systems: New Pump Design Can Help Save Energy
- Innovative Building Materials: Definitive Guide to Radiant Floor Heating Systems
- Radiantec: Installing Tubing Within a Subfloor
- Energy.gov: Radiant Heating
- Warmup: Pros & Cons of Radiant Floor Heating
- Infloor Heating Systems: Why Does Infloor Radiant Heating Feel So Comfortable?