Everything a Homeowner Needs to Know About Radiant Heat Systems

Radiant heat is nothing new — the heating systems in many vintage North American homes consist of radiators fed with hot water or steam by a boiler in the basement. Every time you turn on an electric resistive space heater or bask under a gas-fire patio heater, you're bathed by the radiant heat from the heating elements, and when you stand in a sunny spot on a cold day, the warmth you feel comes from — you guessed it — radiant heat from the sun.

In-floor radiant heat has a long history. The ancient Chinese, Koreans and Romans built raised floors under which they circulated hot air from a fire to warm the floor. What's new is how technologically advanced radiant in-floor and space heating has become. The most efficient modern radiant heat systems are hydronic, which means they use hot water heated by a gas or electric boiler located in the basement or a similarly convenient place. Electric floor heating elements connect to the home's circuitry, and because they use electricity, they are less energy efficient and are generally used to warm a floor rather than an entire room. You can also install hydronic or electric heat in wall panels and even in the ceiling, although this isn't as common as in-floor heat.

Radiant heat is comfortable heat, and if you doubt that, go back to that sunny spot and feel the difference between the warm rays and the cold air around you. Radiant heat reaches through the air and warms your body directly. Homeowners who like the idea of in-floor heat can add it to their existing home — it's even a potential DIY project — but the best time to install it is while the house is being constructed.

The water that circulates through a hydronic heating system starts its journey at the boiler, which is a gas or electric water heater that works essentially like an on-demand water heater. From there, the water travels through a pipe to a manifold, which is a junction point that splits the pipes into separate zones, each one serving a particular room or part of the house. The water then travels through pipes embedded in the floor, walls or ceiling, surrenders the heat to the flooring material (which in turn radiates it into the room) and then returns to the boiler.

Something has to keep the water circulating, and that's the job of a small, efficient electric circulation pump, the most efficient of which uses no more energy than a light bulb. The only other energy you need for radiant floor heating is that required to heat the water, and all gas-fired boilers are required by law to be at least 80 percent efficient. No blowers are needed, and there's no heat loss through ductwork, so radiant floor heating can save 30 percent or more in monthly energy costs over forced-air heating.

A typical electric in-floor heating system is far simpler, consisting of only three components: the heating cable, an in-floor temperature sensor and an in-line thermostat. It can operate at 120 or 240 volts depending on the coverage area. The higher voltage is used for larger areas to keep the current draw manageable. Systems typically consume from 6 to 12 watts per square foot, making power consumption in a 100-square-foot room between 600 and 1,200 watts, which is less than a standard electric space heater.

Any object that radiates heat feels warmer the closer you get to it, and since you are close to the floor, you feel warmer. Whereas forced-air systems warm the air, which then swirls around the room and migrates toward the ceiling, radiant floor heating, at least 50 percent of which is in the infrared spectrum, keeps your feet warmer than your head. The temperature required for comfort is in the range of 75 to 80 degrees Fahrenheit rather than the 120 to 140 degrees generated by forced-air systems.

Heat from radiant heat systems is uniform and even, lacking the cold spots that are typical when heat is blown into the room through ductwork. No matter where you go in a room with radiant heating, you won't feel cold unless you leave a window or door open. Even then, you won't feel as cold because the heat isn't riding on air currents and won't be carried outside on a draft. Close the open door or window and you'll immediately feel the warming effect of the heating elements in the floor.

You can get the same type of heating effect from radiators, radiant panels in the walls and hydronic baseboard heaters, but it's more localized — the farther you are from one of the heaters, the colder you feel. When the heaters are in the floor, you're always the same distance from them. Because the heat is uniform everywhere in the room, you don't need as much, so you can lower the thermostat and use even less energy.

The pipes for hydronic floor heating systems are usually made of PEX tubing, and they are incorporated into the subfloor in one of two ways. They may be embedded in fresh concrete in a concrete slab foundation, which is best accomplished during new construction, or embedded in a layer of fresh concrete on top of the joists of an existing foundation. This is known as a wet installation. In a dry installation, the pipes are installed between subflooring planks slightly thicker than the tubing diameter, and the floor covering, which can be hardwood, laminate, vinyl, ceramic tile or low-pile carpeting, is installed over them.

The wet method is used most often when installing electric radiant floor heating. You install the heating cable, which comes on a spool or attached to sheets of plastic meshing, by affixing it to the subfloor with hot glue and then you cover it with thinset mortar or floor-leveling compound, leaving one end of the cable exposed so you can connect it to power. Once the mortar or leveling compound sets up, you install the floor covering.

A simpler dry installation method is to attach hydronic tubing or electric heating elements to the underside of the joists or pull them through holes drilled in the joists. This method doesn't supply as efficient heating as a wet installation, but it is less intrusive and can be accomplished without removing the floor covering. The simplest installation method of all is to lay an electric radiant heating mat directly on the floor, either exposed or hidden under a carpet, and plug it in.

The cost of installing radiant heating tubing for an in-floor hydronic system costs about $13 per square foot on average, and that doesn't include the cost of the boiler, which can cost anywhere from $1,500 to $7,000 depending on the size of the system. Boilers often double as water heaters (the ones that do are called combi-boilers), so if you need a new water heater, you can get one for free by installing a hydronic heating system. All in all, expect to pay somewhere in the neighborhood of $20 per square foot to install a new hydronic radiant heating system.

An electric in-floor heating system costs $9 to $12 per square foot to install not counting the floor covering you need to install over it. That's considerably less than a hydronic system, but because electricity is more expensive as a heating source than gas, electric systems cost more to operate. This is one reason electric radiant heat systems are best employed to make the floors in individual rooms more comfortable rather than as a whole-house heating solution.

A hydronic or electric radiant floor system doesn't ventilate, and while that means it won't broadcast dusty hot air filled with allergens through the house — which is a good thing — it won't cool your house either, although you can always install minisplit air conditioners in the rooms that need cooling. People who live in a new house that has been tightly constructed may opt for radiant heat and still need ductwork or small vents for air exchange. Despite this, the energy-efficient operation of an in-floor hot-water heating system will save you money over the cost of running a central air system in the long run. If you choose to keep your central air system, an electric in-floor heating system can provide that extra comfort on cold days and make it that much easier to get out of bed.