Radiant Floors for heating and cooling - Energy Efficient Building

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Applications > Radiant Floors
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Concrete with embedded tubing can provide space heating and cooling. Concrete radiant floors use the thermal mass and conductance of concrete to spread heating and cooling throughout the floor and maintain a constant, even temperature. Rather than heating the air, which naturally rises in conditioned spaces during cold weather, radiant floors warm objects. Although hot water and electricity are the most common heating source, systems can be designed for use with solar and other energy sources. Chilled water is the most common cooling source. Use of radiant floors has been growing exponentially since the early 1990’s.

Slab on grade installation of radiant floor (Photo courtesy of Radiant Panel Association)

The two primary types of concrete radiant floors are slab-on-grade and thin slab on a subfloor.

For a slab-on-grade installation, tubing or electric heating elements are tied to wire mesh or placed on fixtures that hold them in place before the concrete floor is placed. The tubing or heating elements are embedded beneath the slab or anywhere up to 2 inches beneath the floor surface, depending on the design and installation procedure selected. Insulation should be installed beneath the energy source and slab to force the heating or cooling up into the slab and minimize energy losses to the ground.

For the installation on a wood subfloor, tubing or electric heating elements are attached to the wood subfloor with fasteners that hold them in place until the concrete is in installed as the final floor. Concrete is often separated from the subfloor with a slip sheet to prevent bonding. A rigid, non-flexing subfloor is required to prevent the concrete floor slab from cracking.

Concrete radiant floors can be used in both residential and commercial/industrial applications as:

Floor warming, to provide warmth in a family room or eliminate cold bathroom or entry way floors
Space heating and/or cooling, as the primary heating system for a room, house or commercial building
Space heating and cooling can also be provided by embedding tubing or heating elements into concrete walls.

This 3-in. thick, cast-in-place concrete floor with hot water radiant heat was installed on a wood subbase. The 3/4-in plywood subbase was installed on wooden I-beam joists. The finish consists of an acid stain to provide color. Trash bags were placed on the surface during curing to provide the texture. (PCA No. 15179 and No. 15183)

Radiant floors offer a range of benefits. For more detail see associated sustainability solutions to the right as well as cast-in-place.

Quiet: Radiant floors offer acoustical comfort due to the quiet (non-mechanical) delivery of heat.

Thermal Comfort: Concrete radiant floors provide thermal comfort, by delivering even heating and cooling. Radiant heat warms the floor, room contents, and people rather than the air. Radiant cooling cools the floor, room contents, and people.

Recycled content: The concrete can contain recycled content materials such as fly ash and slag cement as a partial replacement for portland cement . May contribute to LEED Credit M 4.

Energy Efficiency: Because concrete radiant floors enhance thermal comfort, energy requirements are reduced. Energy savings of 10% to 30% in most residences and up to 60% or more in shops, hangars and warehouses are possible. May contribute to LEED Credit EA 1.

Indoor Air Quality. Radiant floors when finished as concrete reduce the need for other flooring which can introduce VOCs or harbor dust and other particulates (carpet). They also eliminate forced air systems that require filters to be maintained and can themselves contribute to air quality concerns.

Solar power friendly. Solar water heating is easily implemented with hydronic radiant heating systems.

Temperature Control: The temperature is controlled by a room thermostat or a floor sensing thermostat. A room thermostat controls the room temperature using a wall-mounted device similar to that used in space heating. Each room can have its own thermostat, which can be programmable if desired. This saves energy because rooms not used can be maintained at low temperatures. A floor sensing thermostat uses a wall-mounted thermostat to control the surface temperature of the floor.

Radiant heating and cooling provides comfort even though the floor feels neutral and is not warmer or cooler than body temperature most of the time. In the heating mode, the floor feels warm to the touch only on very cold days when the maximum output is required. Because thermal mass changes temperature slowly, owners need to be educated to optimize their use.

System Type: Electric systems are easy to install and have a lower first cost. Alternatively, hot water systems can use almost any fuel source - natural gas, propane, oil, wood, solar, or electricity – and are quite versatile. The choice between electric and hot water would be based on cost of fuel, project size, and client preference.

The standard power used for residential floor heating is 8 to 12 watts per square foot (27 to 40 Btus/sq ft). So, the energy required to heat 10 square feet is equal to a single 100-watt light bulb (while incandescent bulbs are very inefficient for lighting, they are quite good at producing heat).

Cooling: For summer cooling, a separate air-conditioning system is often installed. However, some radiant systems circulate cool water through the floor.

BOOKMARK

Radiant Flooring Guide

Radient Panel Association.

Available for download for free. This publication is designed to help homeowners and building designers understand their choices. It includes information on how radiant floors work, how to include radiant floor in your design, hydronic (hot water) and/or electric, product directory, gallery of radiant systems, resource guide, selecting floor coverings for radiant floors: wood, decorative concrete, tile, stone, marble, carpet, laminate flooring, resilient flooring.

What's Your IAQ I.Q.? (1999)

Environmental Council of Concrete Organizations, #2846

Architects, engineers, and builders are becoming more proactive in assuring the Indoor Air Quality (IAQ) of the buildings for which they are responsible. Concrete is the best building material for forestalling sick building syndrome. Concrete also reduces the outgassing of indoor air pollutants. Because concrete structures are more energy efficient, they lower emissions form furnaces. This document is available for free from Environmental Council of Concrete Organizations. To find this article: Follow the link provided, then click "catalog" and scroll half way down the page to find the article.

Concrete Homes

Portland Cement Association

A web resource for general information on concrete homes.

Radiant Panel Association (2006)

An industry resource website.

U.S. Environmental Protection Agency (EPA) Indoor Air Quality website