Radiant heat isn't exactly a new idea. Turkish and Roman baths were often constructed on raised floors so warm air could circulate underneath and keep things comfortable. Incorporating radiant heating systems into modern dwellings didn't become popular, however, until the mid 20th century. Radiant heat has many advantages over other central heat systems, such as forced air, but installation cost isn't one of them, especially if you want to add radiant heat to an existing structure. This can be an expensive alternative. However, radiant heat can be one of the most environmentally friendly heating options when used in conjunction with solar heating panels.
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What Is Radiant Heat?
Hydronic Radiant Floors
Unlike in a Turkish bath, the radiant heat in a modern system comes from pipes or electric heating elements embedded in the floor or installed in the joists underneath. In a hydronic system, water circulates through a boiler, which maintains it at a temperature warm enough to heat the floor. This type of system is less costly to operate than an electric system, especially if you supplement the energy source needed to heat the water by using solar panels.
The pipes that carry the heated water in a hydronic system are often embedded in concrete, because concrete is a good thermal conductor. The pipes in older systems are usually copper, but newer systems employ polyethylene (PEX) tubing, which is more versatile and easier to install. PEX tubing can even be installed in existing joists, so it is possible to have radiant heat under your hardwood or tile floor without having to tear it up.
Electric Radiant Heat
The elements in an electric radiant heat system are typically embedded in mats that go between the subfloor and the floor covering. The best time to install these is when you're replacing the floor covering. If your floor isn't due for replacement anytime soon, you can also buy mats that fit between the joists and install them from underneath the floor.
Three Types of Hydronic Systems
You can choose from three different hydronic heating systems: closed, open or heat exchange.
Closed system. The boiler is dedicated to the heating system. The main advantage of this type of system is that you can use antifreeze instead of water as the circulating fluid, which can be beneficial in colder climates where the piping may be exposed for various reasons. Antifreeze has its drawbacks if not maintained or used properly. It also has less heat transfer rate than water and makes any pumps work harder. For instance, a system with 25 percent antifreeze can have a 5-10 percent loss of heat transfer compared to just water.
Open system. A water heater supplies hot water to bathrooms and kitchens as well as the heating system. You save money because you only need one water heater. Due to the lower temperatures (100-120 degrees) of hydronic radiant heat, a water heater can be used.
Heat exchanger. A heat exchange system combines the benefits of both open and closed systems. The pipes that supply the radiant heat system pass through the main water heater, but they are sealed and usually circulate antifreeze instead of water. And you can get creative with a heat exchange system and tie it to a solar heating panel. The pipes from the panel can circulate antifreeze through the water heater as well as the floor, lowering your water heating costs while also providing heat for the house.
Pros and Cons of Radiant Heat
On the plus side, a radiant heating system puts the heat exactly where you need it—under your feet. As the warm air rises, the room quickly becomes uniformly and comfortably warm without the drafts and convection currents associated with forced air.
Another advantage over forced air is that a radiant system has fewer moving parts. The only components you have to service are the boiler—which can double as a hot water heater for the bathroom in a pinch—and the circulation pump, which is a relatively inexpensive item. You'll be happy you have radiant heat when the power goes out during a winter storm, because the floor retains heat for a few hours.
The main drawback of radiant heat is its installation cost. This probably isn't a problem if you're already building or renovating. But if you aren't, the cost, which can approach $9.00 per square foot in a smaller house, can definitely be a factor.
Another disadvantage is that a radiant heating system doesn't work well as a cooling system. If you need both heating and cooling, it's usually best to go with a forced air system or install a ductless mini-split system for warm weather comfort in addition to the radiant heat.
As far as electric radiant heat is concerned, it's best suited as a supplement to your existing heating system. It consumes too much electricity to make it practical as a stand-alone heating system for the entire home.
Compatible Floor Coverings
Not all floor coverings conduct heat well enough to work with radiant heating systems. The best choice is ceramic tile, which conducts heat as well as concrete. Laminate and stone flooring, as well as solid and engineered hardwood, are also suitable. Carpeting and vinyl flooring, however, are not good choices. These materials are poor conductors of heat, and are more likely to trap heat than to allow it to radiate into the room.
Should I Go with Radiant Heat?
If you're building a new house or you're considering a major renovation, radiant heat should definitely be on your list of options, particularly if the house has high ceilings. The best time to install a radiant heat system is when you're building the floors. Adding radiant heat to an existing structure is more labor-intensive and expensive, but it might make sense if you already have a large, underused water heater in good condition. Keep in mind that you don't need radiant heat in every room. You'll probably want it in the bedrooms, bathrooms and living room, but hallways, closets and laundry rooms don't need the extra warmth.
If you're on the fence, you can always give radiant heat a test run by purchasing an under-carpet heating mat. This provides the same type of warmth you'd get from an actual radiant heating system, and the installation costs are zero.