Long ago, the Romans used radiant floor heating in their bathhouses. For centuries, the Koreans heated their royal palaces and traditional homes in this manner. Today, radiant heating technology has been improved and can be used in all or part of our homes.

What is radiant floor heating?

Radiant floor heating is a method of heating your home by applying heat underneath or within the floor. Comparable to warming yourself in the sun, this type of heating warms objects as opposed to raising the temperature of the air.

Figure 1: Hydronic radiant floor heating tubing laid out in specific heating pattern prior to concrete pour.

Photo courtesy of Ready Mixed Concrete Association of Ontario.

There are three types of radiant floor heating: hydronic, electric and air. This About Your House document focuses on hydronic (water) radiant floor heating.

Brought to North America post World War II, the first generation of North American systems met with several mechanical failures. The introduction of carpeted floors reduced the system efficiency. Today, significant improvements have been made in both the heating component and the system design.

Hydronic radiant floor heating is a system of plastic or metal tubes/pipes laid within a floor that carries hot water into specific rooms or "zones", dispersing the heat through the floor surface (see Figure 1).

The cooler water returns to the heat source where it is reheated and sent out again in what is known as a "closed-loop system". The pipes can be encased in a concrete slab, a concrete or gypsum cement overpour, laid into thin grooved panels that nail on top of a subfloor, or suspended below a wooden subfloor using metal fins fastened under the floor surface (see Figure 2). The heat output is determined by pipe spacing, water temperature, flow rate and floor covering. The heat output must be calculated to meet the heat loss demands of the home.

One type of tubing commonly used is a new leak-resistant, non-toxic, high temperature, flexible piping called cross-linked polyethylene (PEX). PEX is a durable tubing that doesn’t become brittle over time and isn’t affected by aggressive concrete additives or water conditions. PEX has been used in Europe since the 1970s and was introduced to North America in the early 1980s.

Figure 2: Suspended in subfloor.

Image courtesy of Wirsbo Co.

Is this type of heating available in both new and existing homes?

Yes. While the system can be easily designed and installed in new construction, homeowners wishing to renovate may incorporate hydronic radiant floor heating throughout the home, given certain conditions exist:

the building structure can support the additional weight of the concrete/cement overpour, or

the underside of the subfloor is accessible, or

if being added to the basement, there is enough height for a concrete overpour above the insulation. (If the concrete floor is already insulated below, additional insulation is not necessary.)

Entire House Versus Selected Rooms

Homeowners can chose to install hydronic radiant floor heating throughout the house, or in selected rooms (see Figure 3). The most popular rooms with this type of heating are the bathroom, kitchen and living room–rooms where the most time is spent. If only selected rooms have this type of heating, then a separate heating and ventilation system is required to heat the remainder of the home. The system can also be "zoned" so that there are temperature controls for each area.

DESIGN

Prior to the installation of a system, a qualified floor-heating specialist should make a heating-load estimate of your home on a room-by-room basis. The heating-load estimate will assist in an efficient system design. By placing the tubing in specific patterns and spacings, the system can accommodate the insulation of the room/home and flooring choices.

Figure 3: Hydronic radiant floor heating throughout a home.

Note: Pipes are not visible when installation is completed.

Once designed and installed, a copy of the design should be given to the homeowner, should pipes/tubing need to be located at a later date. When renovating, extra care must be taken that piping or tubing not be punctured.

Exposed surfaces that conduct heat well are best for radiant floor heating, such as finished concrete or ceramic tile. It should be noted that if any later flooring renovation is undertaken, the hydronic radiant floor heating installer should be notified to make any required adjustments to the heating system. For example, the water temperature of the heating system would need to be adjusted if there was a change from a bare or painted finished floor slab to ceramic tile, or wood flooring or to carpet with underlay. Wood flooring and thick carpets act as an insulation blanket, restricting upward heat flow and reduce the efficiency of the system.

SYSTEM COMPONENTS

There are three components to this heating system: a heat source, a distribution piping system and controls. The heat source in hydronic radiant floor heating is usually a boiler or a hot water heater, but other heat sources can be used too. The energy used to heat the hot water can be natural gas, oil, electricity, propane, wood or solar hot water collection.

A circulator pump near the water supply manifold moves the water from the mixing valve to the supply manifold into the distribution piping system (tubing) inside the floors. Properly designed, this delivers even heat to rooms. A properly designed radiant floor system will not exceed 29ºC (85ºF).

To select how warm or cool a room or home will be, controls are required to set the system to a particular temperature. A manifold system with thermostat or aquastat switches typically located in an accessible wall cavity provides a series of simple valves that are used to regulate the flow of water through each zone. There is a caution not to exceed the recommended maximum temperature as it could warp solid hardwood flooring and cause stress to the system.

INSTALLATION

There are three choices of installation:

Slab-on-grade system: One example of a slab-on-grade system is PEX tubing attached to a wire mesh or clipped onto rigid Styrofoam insulation. Concrete is poured over the piping or tubing at the ground "grade" level. The slab must be insulated from the exterior side of the floor all the way to the slab edges.

Thin slab system:

The floor heating tubing is fastened above the subfloor and is covered with lightweight concrete or selflevelling gypsum cement underlayment. The floor ranges in thickness from 3.2 to 3.8 cm (1.25 to 1.5 in).

Another version is to sandwich the tubing between the subfloor and the finished floor. This raises the floor only 1.3 cm (1/2 in). There are a variety of new underlayment panels that hold the tubing in place and incorporate aluminum transfer plates to improve heating performance.

Dry or "Plate" system: Tubing is attached to the underside of the subfloor, also known as a belowdeck or joist space dry system. In cold weather climates, tubing should be attached with aluminum transfer plates and both well insulated for improved performance. Without the insulation, the warmth will disperse into the basement. It is also possible to have an abovedeck dry system, where heat transfer plates are supported by sleepers.

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