Warm floors, anyone? If you’ve ever experienced radiant floor heating for yourself, you know the comfort it can delivers. And if you have it in your own home, you know the added energy efficiency it can provide compared to traditional forced-air HVAC systems.
So when you’re designing a home, do you ever consider radiant floor heating? The benefits of the system abound: quieter (no noisy fans), better indoor environmental quality (no dust or allergens blowing around the home), no ductwork and no floor vents (for freedom of furniture placement) … the list can go on and on. And radiant floor heating can work under any floor covering from traditional carpet, tile and hardwoods to more exotic surfaces such as slate, cork and bamboo. It even works under concrete (quite well, in fact).
Radiant floor heating is not a new concept; it’s a technology that has been around since the Roman times. It is also the primary method for indoor comfort throughout Europe where the climates can be much colder compared to areas in the U.S.
In a hydronic radiant floor heating system, warm water circulates through flexible tubing placed under or within the floors. As the warmth from the water radiates up from the floor, it warms the people (and the objects) throughout a room. The best part of all, a radiant system is designed in zones, which means each room can have a different thermostat setting. This adds to the efficiency of the system because rooms with less traffic (such as a den or guest bedroom) can be set at a lower temperature setting than a master bathroom or basement which might need additional heating for comfort.
So what are the different methods for installing radiant floor heating systems? They can vary depending on the design of the home, but here are the top five typical installation methods that are used in residential construction today.
This is one of the more common methods for residential new construction. The staple-down method incorporates either metal staples for wood subfloors or plastic staples for foam insulation on a concrete slab. The installer simply “fastens” a flexible plastic tubing called PEX to the surface using a special tool. The staples go around the outside of the tubing (not through the tubing) and then adhere to the surface below. After the tubing is completely fastened to the surface, a lightweight concrete overpour goes over the tubing to create a smooth, solid surface for the flooring.
Aluminum is an excellent conductor of heat, so using aluminum heat-transfer plates is a very effective way to install a high-performing radiant floor heating system in a home when concrete overpour on the surface of the floor is not an option. The plates fasten to the underside of the subfloor between the joists and
feature a channel down the middle where the tubing locks into place. A “stamped” aluminum heat-transfer plate features the tubing channel on the face (or top) of the plate that fastens to the subfloor, so the tubing must be installed first and then the plate is fastened to the underside of the subfloor. An “extruded” aluminum heat-transfer plate has the channel on the underside of the plate, so the plate can first be fastened to the subfloor and then the tubing can be installed. Note that after installation, it is important to add a minimum R-11 fiberglass insulation into the joist bay snug against the plates to prevent downward heat loss.
Knobbed mats are becoming more a more widely used option for radiant floor heating due to the ease of use for tubing installation. The mats come preformed with knobs throughout the surface which make it easy to “snap” the tubing into place. The installer simply adheres the mat to the concrete slab or wood subfloor and presses the tubing between the knobs. Typically, an installer can simply “walk” the tubing into the mat by pressing on it with a foot, eliminating the need to bend down to touch the surface. After the tubing is installed, it is then covered with a lightweight concrete overpour to create a smooth, solid surface for the flooring.
With typical thicknesses of only a half inch, wood radiant panels are an ideal solution for remodel and retrofit applications. The panels simply fasten to the plywood subfloor and feature a groove down the center for the tubing placement. An aluminum sheet on the bottom of the panel increases the heat transferability. This method offers several advantages in addition to the minimal increase in floor height, including no moisture from concrete overpours and increased BTU output potential over joist heating.
This method is most appropriate for “floor conditioning”—the warming of floors without providing heat into the space. The clips simply fasten to the underside of the subfloor between the joists and suspend the PEX from the subfloor. Like aluminum plates, it is important to add fiberglass insulation after the tubing is installed. However, unlike aluminum plates where the insulation must be snug against the plate, in joist clip installations, there must be an inch gap between the PEX tubing and the insulation. This creates an air gap below the subfloor which will enable the heat to better transfer to the floor.
On a side note, another method that is typically used in commercial construction but can also be used for ground-level areas of a new construction home is wire ties. The wire-tie method is used for installations on
or below grade. It requires a compacted base material such as dirt, sand or gravel with a wire mesh or rebar grid placed over the ground. The wire ties affix the tubing to the wire mesh or rebar (typically every three feet) to ensure the tubing stays in place as the concrete is poured over the tubing and wire mesh or rebar grid system. It is important to note that when doing this type of installation, there can be under-slab heat loss which can hinder the system’s performance. Under-slab insulation is typically necessary to ensure heat is not lost to the ground.
Whatever the installation method used, it is most important to ensure a radiant professional designs the system. A perfectly installed system will not have the ability to perform efficiently if it is designed improperly.
Several factors go into the design of a radiant floor heating system, including room size, heat loss, solar gain, loop lengths, number of zones, heat source and pump sizing. So when it comes time to design a home with radiant, be sure to have the right professional on your side (otherwise you could end up with unhappy homeowners).
But when a system is designed right and installed correctly, it is the most luxurious, comfortable, energy-efficient and sustainable method for heating a home, hands (and feet) down.
Kim Bliss is the technical communications manager at Uponor. She can be reached at email@example.com.