How Radiant Floor Heating Works

When you select a radiant floor heating (RFH) system, you'll choose either electric or hydronic. The amount of power it takes to heat an entire house with an electric RFH system isn't cost-effective, so if you're heating your whole house, then hydronic is the way to go. Are you building a new house or renovating an older home? If it's new construction, a hydronic system is probably the best choice. You can install hydronic systems in an existing home, but you'll have to tear up the flooring, which is expensive and a lot of work.

 

Let's say you've decided on a hydronic RFH system. The first thing you should know is that it'll cost you more upfront than a standard furnace unit. A forced-air system for a 2,000 square foot (610 square meter) home will cost about $3,800 to $4,500. A hydronic radiant floor heating unit with a boiler will run $7,000 to $13,000. The RFH system is more efficient though, as much as 40 percent, and lasts longer. Standard furnaces last between 10 and 25 years, while the RFH system will get you up to 40 years' use.

A hydronic system offers another advantage -- you can use a variety of sources to heat the water:

 

Deciding which heat source to use depends on how large your house is and how cold it is where you live. For example, if you have a large home with high ceilings and live in Canada, you'll most likely need a boiler system. On the other hand, if you're building a smaller home in Florida, you can get away with using your regular water heater.

 

So you've decided that you need a gas-fired boiler system on your newly constructed home. Before the flooring is put in place, your RFH specialist or general contractor will need to install your system. There are two types of installation -- wet or dry. Wet installs layer either a slab of concrete beneath the subfloor or a thin sheet of concrete between the subfloor and the surface. Dry installs place the tubes directly beneath the subfloor during construction, without the concrete on top. The flooring surface -- hardwoods, tile or carpeting, goes on top of the subfloor and picks up heat directly from the tubes.

 

The concrete acts as a thermal mass to retain heat so that you have a large, hot block under your floor. Concrete owes its ability to retain heat to its density and low conductivity. Wood has a very high conductivity -- think of how quickly wooden decks or benches cool off when the sun goes down. Because of this thermal mass, systems with wet installs take longer to heat up and need to run longer. Those with dry installs are less expensive, but operate at higher temperatures because there's no thermal mass to store the heat. They also require reflective insulation under the tubes to direct the heat upward.

 

Your boiler or water heater is linked to a manifold -- a system of separate pipes that channel water from a single source into different zones. This way, you can heat each area of your home separately from a single programmable thermostat. From the manifold, the hot water is sent through a pattern of PEX tubing by a re-circulating water pump. PEX is polyethylene tubing that's leak-free, non-toxic, flexible and capable of handling high temperatures.

 

Maintenance for a hydronic system is minimal -- the boiler needs an annual check-up, but most modern pumps use water to lubricate the parts and are low-maintenance. However, if your system breaks, you'll need to hire a professional, because fixing it can be complicated. It's also expensive. In some cases a unit is beyond repair and must be replaced, which costs about the same as a first-time installation.

 

There are lots of variables, but the good news is your RFH specialist can walk you through the different options.

 

Now that we've learned about hydronic RFH systems, let's learn the about electric RFH options.

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Electric radiant floor heating (RFH) uses heat-conducting plastic mats containing coils warmed by electricity. So what are these heating coils? They aren't heated elements like you'd find in a space heater or on an electric stove. They're actually resistance wires, typically copper or nichrome, wrapped in a water-resistant polymer. Nichrome is an alloy of nickel and chromium with high electrical resistance -- ideal for producing heat. These wires are zigzagged through a mat and then wired for electricity. Think of a large, rolled-up electric blanket without the fabric and you'll get the picture.

On installation day, you or your contractor will roll out the mats and put the flooring material in place. Most people choose to go with electric RFH just for individual rooms since the cost of electricity makes this system quite expensive for heating an entire house. You can save money if your local power company charges less for off-peak usage. Cheaper nighttime power rates allow consumers to charge the heating elements overnight for less money -- then the heat is used over the course of the following day.

Electric RHF works best with floors made of ceramic tile, but it can be used with most types of flooring, including hardwood floors. Carpet is thicker and doesn't conduct heat as well as tile or hardwood flooring, but selecting the correct padding can greatly increase the amount of heat you'll get. There are two kinds of padding used on carpets -- slab and ribbed. Slab pads are flat and ribbed and have a waffle pattern. A 3/8 inch (.68 centimeter) slab foam rubber pad is recommended for RFH systems with carpeting.

Because an electric RFH system is usually used for single rooms, it's controlled either with a simple flick of a switch or automatically by thermostat. Since electric RFH system heating coils are installed between the subfloor and the floor covering itself, heating time is short. It typically takes about 30 minutes to an hour to heat your floor and room. Set the thermostat to turn up the heat an hour before you get out of bed, and warm, cozy bathroom tile will be ready to greet your bare feet.

For a small bathroom, you'll spend in the neighborhood of $400 to $800 to install an electric RFH system, and you can even do it yourself. It's no harder than laying tile, but you'll need a qualified electrician to wire the system to a thermostat. Unfortunately, there's no way to install the heating mats without first tearing up your existing floor, so the ideal time to make the switch to an electric RFH system in your bathroom, sunroom or kitchen would be during a renovation. Once the flooring is removed, just lay the mats and tile over them. The tile glue and grout won't affect the heating mats. Once the flooring is back in place, you can literally forget about the heating mats -- they require no regular maintenance.

When you factor in the cost of a radiant floor heating unit, keep in mind that electric systems rarely have problems. When they do, a homeowner can troubleshoot and make most repairs. Make sure to turn off the power before inspecting, repairing or replacing any panels.

Electric or hydronic, RFH offers a number of home heating options. To learn more about home heating and construction, please visit the links on the following page.