By now, you know that space conditioning—heating or cooling living areas—accounts for about half of your household energy costs. Insulating and weatherproofing will help you control the indoor climate, but you still have to decide how to provide heat and cooling.
One method of heating that has become popular in recent years is radiant in-floor heat. It involves either wire mesh that converts electricity into heat, or flexible tubing through which hot water is circulated. Both versions provide easy, invisible comfort. They have different requirements, though, so consider the details carefully before you decide which to use.
Traditional Space Conditioning
Early furnaces and boilers used gravity to help circulate heated air and water through a house; later models added fans and pumps to improve range and control. Both methods involved large, bulky, complex conduits: ducts and registers for air heat, or pipes and radiators for hot water. Air supply and return registers take up little room in your living spaces, but the ducts shape the way the entire inside of your house is put together. And pipes that run to and from hot water radiators take up less space than air ducts, but the radiators are large, heavy, obtrusive, and generally immovable.
These traditional methods of heating have other drawbacks as well. Forced-air systems create excess pressure inside the house, which increases the flow of indoor air to the outside. This contributes to heat loss in the winter and reduced cooling efficiency in the
summer. Moving air also keeps dust, pollen, and other irritants in circulation, aggravating allergies and asthma.
Hot water radiators will not disturb the air, which makes them better suited for people with respiratory ailments. But they can’t be used for cooling, and are often part of an older boiler system that may no longer be efficient. Hot water radiators can be moved if the entire
system is shut down and drained, the pipes are disconnected and reconfigured, new holes are drilled in floors and walls, the system refilled, and air bled from all the radiators. For practical purposes, hot water radiators are an all-or-nothing proposition.
In-floor Heating Systems
Electric floor heat has several features that make it an appealing do-it-yourself project. First, it only requires standard 110 to 120 volt household current. Some kits consume as little as 120 watts, about the same as two incandescent living-room lights. The wire mesh can be
attached directly to a wood subfloor, or to concrete with special fasteners. As soon as the mesh is in place, you can install the main flooring surface right on top of it. If you only plan to add radiant heat to one room, this approach is the simplest.
Radiant heating that uses hot water is called a hydronic system. Installation is more involved than for electric floor heat. Instead of a wire mesh in a fixed size that is simply spread out to cover an area, a hydronic system requires tubes to be routed in a way that covers the area without overlapping. To hold the tubing in place, special brackets are fastened to the subfloor. The tubing then has to run to and from heating and regulating equipment. This scale of project is usually, though not always, more appropriate for new construction.
New Construction
When you are building an entirely new floor, you can plan for radiant floor heating with few compromises. The area will be open and available for a thorough installation without shortcuts or deviations. This provides the best setting for a hydronic system. With full access, you can route the tubing exactly where you want it to go, and create the framing necessary for pouring a gypsum cement or concrete floor around the tubing. Then, if you install ceramic tile as the top surface, your floor will be strong, stable, and warm.
Hydronic systems offer some advantages over electric ones. They can be powered by a variety of energy sources, which can make a significant difference if electricity is expensive in your area. To provide the hot water needed for a hydronic system, you can use a water
heater that runs on natural gas or liquid propane, a boiler that burns wood or runs on electricity, or other sources such as solar collectors, heat pumps, or geothermal energy.
Once the water is heated, it circulates quickly through the tubing—but you won’t hear it the way you can a forced-air furnace or even a hot-water pump. It’s almost silent. And because the water retains heat for a while after the heat source switches off, it cools down gradually, not suddenly. Also, because the heat comes from below, you can have the thermostat set a few degrees lower than usual but feel just as warm as before.
The trade-off for radiant floor heating, especially hydronic systems, is between the initial investment and the benefits that follow. A hydronic system will cost more per square foot than most other heating methods. But once installed, it will provide greater comfort
and reliability than any other source of indoor heat. And hydronic systems are as much as 30 percent more efficient than forced-air systems for heating the same amount of space.
Remodeling
If you are renovating or adding on, and your project includes creating or removing and reinstalling a floor, an electric radiant system is easy to add. Once you decide what flooring surface you want, check to see if it is compatible with electric heating mesh. In general, electric radiant heating works with floating floors, most laminates, and vinyl. Two cautions: if the top flooring surface requires nailing, don’t use electric mesh because you could easily damage the mesh underneath; and heated asphalt felt paper smells terrible, so use rosin paper as part of the underlayment instead.
In addition to the electric heating mesh, a floor-warming system has a hard-wired connection to the household electrical supply, a thermostat and a timer. The thermostat lets you control the floor temperature. Depending on the model of timer you get, it can switch
off the heating system automatically after a specified period, or turn it on and off at predetermined times.
This method of heating has its limits. To prevent damage to the flooring surface, the mesh should not exceed safe temperatures for the chosen material. In some installations, that means the radiant floor heating will not be enough to warm the entire room. The amount
of current you need to run the system will depend on its size. If you want or need to create a separate circuit for radiant floor heating, either be sure you can work safely with the electrical service panel, or hire an electrician to help you.
The resistance wires that provide the heat must not be bent or cut. Few rooms provide neat rectangles, though, so most manufacturers will create a mesh to your specifications. Make sure you have this option before you choose. During installation, check the resistance
often to be sure the wires have not been damaged.
Retrofitting
There’s one way to add radiant floor heating without tearing up the old floor or building a new one. If you have access to the underside of the subfloor, as you might in the basement under the main floor, you can add a hydronic system from below. You can find special aluminum plates, designed to be fastened under the floor with self-tapping screws. These plates have integral channels to hold hydronic tubing, which can be routed to a source of hot water. Because the temperature of a single-loop circuit like this has to be carefully controlled, you will need to connect it to a separate boiler, or to a dedicated zone on a
boiler system with an appropriate manifold.
