Radiant Heating
1.Description
2.Advantages
3.Cost and Energy Savings
4.Frequently Asked Questions (FAQ)

1. Description

Radiant panel ceiling systems are similar to other air-water HVAC systems with respect to the arrangement of its components. The important difference is that room thermal comfort is maintained primarily by radiant heat transfer instead of convective heat transfer (as is the case with tube and fin baseboard radiation).

^ Back to Top ^

2. Advantages
The principal advantages of radiant panel heating systems:
  • Comfort levels can be better than those of other conditioning systems because radiant loads are treated directly and air motion in space is at normal ventilation levels.


  • Space conditioning equipment is not needed at the outside walls, simplifying the wall, floor and structural systems.


  • Almost all mechanical equipment may be centrally located, simplifying maintenance and operation.


  • No space is required within the air conditioned room for mechanical equipment. This is especially valuable in hospital patient rooms and other applications where space is at a premium, where maximum cleanliness is essential, or where it is dictated by legal requirements.


  • Draperies and curtains can be installed at the outside wall without interfering with the space conditioning system.


  • Cooling and heating can be simultaneous, without central zoning or seasonal changeover when four pipe systems are used.


  • Supply air quantities usually do not exceed those required for ventilation and dehumidification.


  • The modular panel concept provides flexibility to meet changes in partitioning.


  • A 100% outside air system may be installed with less severe penalties in terms of refrigeration load because of reduced air quantities.


  • A common central air system can serve both the interior and the perimeter zones.


  • Wet surface cooling coils are eliminated from the occupied space, reducing potential for septic contamination.


  • The panel system can use the automatic sprinkler system piping (see NFPA standard 13, Chapter 3, Section 3.6). The maximum water temperature must not fuse the heads.


  • Radiant panel heating and cooling and minimum air quantities provide a draft-free environment.


  • Peak loads are reduced as a result of thermal energy storage in the panel structure, exposed walls, and partitions.


  • Panels can be coupled with other conditioning systems for heat loss (gain), compensation for cold or hot floors, windows, etc.


^ Back to Top ^

3. Cost and Energy Savings

Energy Savings

A radiant heating system is a much more efficient means of heating an environment than a forced flow system. The cost savings from heating hydronically, as opposed to heating with air, can be as much as 25% in fuel cost alone. This is due to the fact that water is a much better medium to transport heat than air is. The actual amount of energy saved is dependent on many factors including how well the building is insulated, the building size, and the climate the building is located in.

Maintenance Costs

Because radiant panels are out of the way, they are not likely to sustain damage from everyday activities. This is particularly important in high traffic areas such as airport walkways where large numbers of people are walking by with baggage or luggage. Also, since the panels have no dust collecting surfaces, they do not need to be taken apart to be cleaned. This means that the panels will not require periodic repainting due to scratches, dents, or cracking that would be caused by disassembly. Cost savings would be realized during building retrofits, or renovations, by using modular radiant panels that can be reused in other locations without any difficulty.

Construction Costs

There are many ways in which radiant panels can save money in the construction of new buildings. One such area is the amount of pipe it takes to connect to radiant panels. Because both the radiant heating panels and the hot water mains are located in the ceiling, there is no need to drop pipe connections down the walls. All the pipework is up and out of the way.

Increased Floor Space

For office or apartment buildings, the leasable area of a room would be reduced by any wall mounted mechanical equipment around its perimeter. Due to the fact that the panels are up in the ceiling, this space is kept free. This means that the total floor space is no longer reduced by the space conditioning equipment.

^ Back to Top ^

4. Frequently Asked Questions (FAQ)

How Is It Different From Conventional "Radiation"?

Heat may be transferred by conduction (warmth transferred by objects that are touching each other), or convection (heat that is carried from a warmer to a cooler body by an intermediate fluid such as air) or by radiation. Most conventional tube and fin "radiators" are in fact, convectors. They heat a space by warming the air that passes by the heated fins. This air, now warmer than the surrounding air, rises due to buoyancy. This is known as free convection. Where the air is moved past the fins by a blower or fan it is called forced convection. In either case the idea is the same, to compensate for perimeter heat losses by circulating warm air within the space.

By contrast, between 75 and 90 per cent of the energy from a radiant panel is propagated by thermal radiation. Thermal radiation is an electromagnetic radiation propagated due to a difference in temperature. Therefore, the heat is transferred to all bodies "seen" by the panel that are at a lower absolute temperature than the panel itself.

Why Are The Panels In the Ceiling?

It is often asked "Why put the panels in the ceiling? Heat rises, doesn't it?" The answer is no, heat does not rise. Warm air rises. The panels are most effective in the ceiling because from there, they are best able to "see" the objects in the room. Lights are placed in the ceiling for maximum effect. This is because from above, it is not obstructed by room objects and its light can be most effectively cast on the surroundings. Light is a type of electromagnetic radiation which has a shorter wave length than thermal radiation. Therefore, as with a light, the optimal location for a radiant panel is the ceiling.

Another reason for placing the panels in the ceiling is so that higher surface temperatures can be used. The rate of radiant heat transfer from the panel is governed by the Stefan-Boltzmann Law, q = S Ts4 , which demonstrates that the radiative heat transfer from a body increases dramatically as its temperature is increased. Radiant ceiling panels are typically operated at 79-85°C (175-185°F). On the other hand, were the radiant panels mounted on the walls or near the floor, safety code dictates that the panels could not be operated at high temperatures. Thus by placing the panels in the ceiling, the panels can be made to produce more output per area by simply increasing the water temperature.

Is this a Proven Technology?

Radiant panel technology is not new to the HVAC (Heating, Ventilating and Air Conditioning) industry. It is a mature, proven technology that has been in use in Europe for over 100 years. Over the last 35 years, the Canadian and United States HVAC industry has employed radiant panels in many commercial and institutional settings. In fact, since the much publicized outbreak of Legionnaire's disease (spread by contaminated central air systems), radiant heating systems have been the choice for U.S. Veteran's Administration Hospitals and, in the last 10 years, over 80% of the new hospitals constructed in the provinces of Western Canada have employed radiant panel ceiling heating systems.

What About Cold Feet...Warm Head?

Cold feet? Hardly. Tests have shown that the floors in a room heated by a radiant panel ceiling exhibit temperatures 1 to 2°C (3 to 4°F) above the ambient air temperature and actually provide a source of re-radiated heat themselves. In fact, where down drafts from cold walls or glazing present design challenges with respect to occupant comfort, radiant panels provide a solution. The ceiling panels warm the wall or window surfaces by direct transfer of radiant energy, significantly increasing the temperature of each. It has been found that even under extreme cold wall conditions (27°F, -2.7°C), the air velocities are non-draft in nature (less than 50 fpm or 0.25 m/s).

Typically, radiant panel surface temperatures are 170 to 185°F (about 82°C). This can cause the directional mean radiant temperature (DMRT) to be 16 to 20°C (30 to 40°F) above the ambient air temperature. By contrast, on a sunny day, the DMRT outside is 30 to 40°C (50 to 70°F) higher than the ambient air temperature. So, if you enjoy being out in the sunshine, you will enjoy the indoor warmth of a radiant panel ceiling.

^ Back to Top ^