Thousands of years ago radiant floor heating was used by the Romans for heating bathhouses and special palaces. The Chinese and Koreans have used floor radiant heat for centuries in palaces and common homes. And for over a century radiant heat as been used successfully in the United States in limited applications such as indoor swimming pools and gardens. In the past 20 years as the result of technological advances in plastics radiant floor heating is gaining increased popularity for all types of commercial and residential heating systems all over the world. In Europe where radiant heating has become the most popular many new and existing homes and commercial buildings are using radiant floor heating. In the United States radiant heating is growing in popularity every year as the ultimate in efficiency and comfort heating system.

What is radiant floor heating?

Radiant floor heating is a method of heating your home by circulating hot water through a special plastic tubing called PEX underneath the floor. By applying heat in this manner the heat radiates from the tubing up through the floor. Exactly like heat from the sun radiant heating warms objects rather than air. Unlike forced air systems which warm air and then transfer the heat to objects such as walls, furniture and people, radiant heat provides the heat where it is needed efficiently and effectively. Forced hot air systems create stratification that cause upper layers of air to be warmer than lower layers so that in a typical room floor to ceiling temperatures can vary as much as 10 to 15 degrees. With radiant heating the floor temperature is warmer than the ceiling temperature creating a reverse type stratification and perfect comfort.

There are three types of radiant floor heating: hydronic, electric and air. The vast majority of applications focus 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. Using regular steel piping in concrete floors resulted in short term failures after 20 to 30 years of use. The steel pipe was placed directly in contact with the concrete and corrosion began immediately after installation. In the seventies the steel pipe was wrapped with a protective barrier but still provided potential for leaks and failures. The introduction of carpeted floors and linoleum created more barriers to system applications and efficiencies. 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 over pour, laid into grooved panels that nail on top of a subfloor, or suspended below a wooden subfloor using metal plates 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.

Figure 2. Suspended in subfloor. Image courtesy of Wirsbo Co.

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.

Can radiant floor heating be installed in new or existing homes ? Yes. Radiant heating systems can be easily designed and installed in new construction, however homeowners wishing to renovate may incorporate hydronic radiant floor heating throughout the home, given certain conditions exist:

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 there are temperature controls for each area.

Prior to the installation of a system, a DESCO Energy floor-heating specialist will 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.

When installing, 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 system may require 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.

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 a high efficiency Trinity boiler for natural gas or propane. The energy used to heat the hot water can also be oil, electricity, wood or solar hot water collection.

A circulator pump at the boiler circulates water around and through the boiler called the primary loop. Another circulator pump moves water from the primary loop through a manifold and into the distribution piping system (tubing) inside the floors. Properly designed and balanced, this delivers even heat to every room. 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. Each room or each floor can be a single zone to be controlled by a thermostat and pump. The manifold system can be a single zone or a series of zones with a series of valves on each loop which can be individually controlled by it's thermostat. The manifold distributing water to each loop is typically located in an accessible wall cavity where the flow of water for each zone is balanced and set according to flow and temperature. There are various methods of controlling temperature for each zone or loop using components such as variable speed injection pumps or thermostats with outdoor rest control incorporated into pumps or valves. Hot water rest is a method of controlling and adjusting the water temperature supplied to the zone or zones or loops according to the outside air temperatures. Hot water reset prevents hot water systems from overshooting by lowering water temperatures as outside temperatures increase and increasing water temperatures as outside air temperatures decrease. Supplying the same hot water temperature to a floor in a room when it is a milder day will guarantee overshooting of the thermostat setting. Radiant heating systems react slowly and a flywheel effect. By only heating objects requires more time to be efficient. Providing too much heat will result in the room overheating. The most common complaint from a poorly designed radiant floor heating system is overshooting of temperature. Design and installation of the system is critical to maintaining exacting comfort. In floor radiant heating is all about comfort and we like to think of radiant heat as Decorating with Comfort. There is a caution not to exceed the recommended maximum temperature as it could warp solid hardwood flooring and cause stress to the system.

There are three choices of installation:

It is required that a licensed technician or contractor of your choice provide final start up and hook up of the boiler and heating system.

An approximate cost of an installed hydronic radiant floor heating system by a licensed mechanical contractor can range from $6 to $12 per square foot. By using DESCO Energy and making this a do it yourself project costs can range from $3 to $6 per square foot or less than half of a contractor quoted system. This cost can be more or less depending on specific heating requirements and energy efficiency results. In addition to the heating system, a mechanical ventilation system is required in the house.

It is recommended that annual maintenance be done on mechanical equipment such as the pumps, hot water heater, controls etc. If there was a problem or failure, it is commonly found in these mechanical parts.

For repairs to the system, the homeowner should contact DESCO Energy or a local licensed technician. Be sure to have your design plan available for tubing location.

To avoid unnecessary repair work, all equipment must be used and maintained in the manner in which it was designed. Homeowners disconnecting controls or moving pumps or failing to have a licensed technician complete the warranty validation form can find themselves requiring repairs and possibly voiding their warranty.

While the heat source in a properly maintained system can last for as long as 30 to 40 years, PEX pipes set in the floor are expected to last more than 50 years. (Some test results indicate life expectancies of 200-300 years.)

DESCO Energy and manufacturers' warranty policies are strongly dependant on certified and qualified mechanical contractors completing the final start up and set up pf the installation. All require Code regulations be followed for the jurisdiction in which the home is being built. Some manufacturers also require that specific devices be field installed to ensure full warranty coverage such as low water cut offs and proper venting materials. There is no difference in warranty between new construction and renovations and the warranty should be given to the consumer in writing.

Installation warranty varies on the heating contractor and their warranty policies. There may be a difference in warranty between new home construction and renovations by the heating contractor.

Benefits

Comfort

Radiant floor heating provides even, comfortable, warmth as there is less air movement with this type of system. There are no drafts with this type of heating, unless it is through the building envelope. The thermal mass (concrete floor) evens out the temperature fluctuations. The floor is warm to the touch.

R adiant floor heating is more economical to operate because the temperature setting may be set lower to 68ºF rather than the usual 70-72ºF providing the same level of comfort. Energy losses are less because no stratification exists. The warmest part of a radiant system is at the floor level rather than at ceiling levels for forced air systems.

Zoning a variety of rooms with the options for different temperatures significantly reduces energy consumption. All electric homes promoted in the 70s and early 80s by electric utilities saved energy due to the ability to zone and control the temperature of each room individually. However if the homeowner kept the same temperature setting in each room the energy costs were exorbitant. It was the ability of the home to zone each temperature setting and adjust for occupancy which was the primary benefit of cost savings. Also electric homes were required to have higher levels of insulation. Those two factors were the cost savings of all electric homes, not the price of the energy. Employing the benefit of individual zoning and control of each room temperature for occupancy in floor radiant heating systems is the largest energy cost saving feature.

Since radiant floor heating has a low operating temperature, a wide range of sources can be used to heat the water-a condensing boiler, a geothermal heat pump or solar or even district heating.

The system is quiet because the only movement is water passing through the PEX tubing by a circulator pump is almost inaudible. The loudest sound in the system is the gas or oil burner which is generally very quiet and is usually located in a separate room or area of the house. .

Unlike conventional forced-air furnaces, radiant floor heating has no ducts or radiators to contribute to dust collection or movement. Note: duct work is required for the mechanical ventilation system or air conditioning.

For residents with allergies or respiratory problems the ultimate solution is reduction or elimination of air movement. The reduction in air movement also creates a reduction in pollution movement. Movement of dust, dirt, pollen, bacterial, and viral spores as well as other infestations which commonly grow in dark duct systems is significantly reduced and in some instances eliminated. This resulting environment is healthier and safer than pollution created by forced air systems.

Hydronic radiant floor heating is virtually an invisible system. Without baseboard heaters, forced air registers etc, furniture layout is not restricted by the heating system. Bathrooms or special use areas with hard floor finishes are well suited to this type of heating.

Due to thermal mass, the system may be slower to respond to temperature changes. Overheating will occur in poorly designed zoned systems. The system is not designed to have the temperature frequently adjusted.

Night setbacks are not practical in most situations as the system is slow to react.

Ventilation must be done separately. Fresh air exchanges, humidification and air conditioning must be achieved by a separate forced air ducted system. A perfect combination to an in floor heating system is in conjunction with a forced air system. In this type of application the radiant system is used for floor warming rather than total heating of the house.

Extra support is needed for the weight of thermal mass topping on a wood floor. If the building structure can't support the weight, then the dry plate system should be considered.

In our library section you will find many detailed articles on designing and installing radiant floor heating systems.