Heated floors

Energy Saving and Comfort

With the movement towards “green” products, the radiant industry is in a good position to offer a product that not only reduces energy use but increases comfort and improves indoor health at the same time in both the residential and commercial market sectors.

Historically, a decline in new housing starts is followed by an upswing in residential remodels. This is another area that radiant has a potential to make inroads, particularly the electric products. Homeowners who might otherwise purchase a new home, scale back and invest in their existing home. Radiant heating can turn basements and four-season porches into very comfortable living spaces. It can be retrofitted into existing homes either from beneath a finished floor via an open joist bay or installed above the sub floor when replacing floor covering.

“Radiant” refers to a distribution method for heating or cooling. In the last few decades, it has become increasingly popular in the U.S. One reason is the extreme comfort that seems to gently come from both everywhere and from no place in particular.

The heat and the cooling comes from the room surfaces – floors, ceiling, or walls. When surfaces are used this way, they are called radiant panels. “Panel” is an engineering term for a surface where at least 50% of the heating or cooling transfer is radiant.

Radiant comfort systems have a reputation for being the best. While systems have become quite upscale, in both expense and technical complexity, there are tremendous growth opportunities in more modest applications as well. Radiant panel systems can deliver superb comfort at affordable cost and minimal technical complexity.

A radiant system can be very simple, even basic, and deliver the same comfortable radiant heat as a very complex system. Radiant panel heating is more comfortable than other kinds of heating because it primarily heats surfaces rather than the air.

Radiant heating is a process which energy leaves the surface of an object and travels to the surface of a cooler object in the form of electromagnetic waves. In some cases, this radiation can be seen. Sunlight, for example, delivers a portion of its energy to the earth as visible light.

In other cases, the radiation is invisible. Radiant energy, having wavelengths longer than our eyes can see, is called infrared radiation or thermal radiation. This is the type of radiant energy most radiant panels emit. All electromagnetic radiation, whether visible or invisible, shares several characteristics:

1. All radiation travels from warmer surfaces that emit it to cooler surfaces that absorb it.
Heat always moves in any direction from warmer to cooler materials, regardless of what mode of heat transfer carries it.

2. Radiation is perceived as heat only after it is absorbed by a material.  
Sunlight travels through 93 million miles of empty and frigid space, where it is absorbed by the earth’s surface. The instant it is absorbed, it no longer exists as electromagnetic radiation. The energy it contains passes to the absorbing material in the form of heat.

3. Any surface can emit radiation to any other cooler surface within sight of it.  
The rate of radiant energy transfer depends on several factors, including:
- The difference in temperature between the surfaces
- The distance between the surfaces
- The angle between the two surfaces
- The optical properties of the surfaces (the ability to emit or to absorb heat)

4. Radiant heat travels equally well in any direction.  
Most people think that heat rises. They are describing the fact that warm air (or other fluid) rises because of its lower density. The fact that radiation travels downward just as effectively as upward is what enables a heated ceiling to effectively deliver heat to objects in the room below.

5. Air absorbs very little thermal radiation.  
This is an extremely important and beneficial characteristic of radiant heat. It is what allows radiant panel heating systems to directly warm objects without first heating the air around them. It explains why people can feel the warmth of a campfire even though the air between them and the file is cold. The radiant energy emitted by the flames is sensed as heat only when it arrives at and is absorbed by skin and clothing.

6. Thermal radiation can be partially reflected by certain surfaces.  
Some surfaces, such as polished metal, can reflect part of the infrared radiation that strikes them just like a mirror reflects visible light. Most common interior building surfaces, however, have low reflective characteristics and so absorb most of the infrared radiation that strikes them.

Advantages of Radiant Heating

A large portion of our body's heat loss is radiation to cooler surfaces surrounding us. The cooler these surfaces are, the faster they pull heat from us and the more uncomfortable we feel. By warming the interior surfaces of floors, walls, ceilings, windows and doors, radiant panel heating reduces radiant heat loss from our bodies. Because we are especially sensitive to our radiant surroundings, this significantly improves comfort. The result is a unique, quiet, warm-all-over feeling.
Most people engaged in light activity will be very comfortable in radiantly heated rooms with air temperatures in the mid 60°F range. If the activity level is greater, light shop work for example, comfort is often maintained with air temperatures in the low 60°F range.
The ideal temperature variation consists of slightly warmer at foot level, around 70° F at chest level and cooler at the ceiling.
Radiant heating eliminates the familiar but uncomfortable situation of warm air blanketing the ceiling while cool air pools at the floor. It improves comfort and reduces heat transfer through the ceiling and upper portions of the wall. It also reduces stack effect air leakage from the building. The greater the height of the interior space, the more beneficial this characteristic is. The need for paddle fans to push warm air back down to the occupied area of the room is often eliminated.
Whether constructed with hydronic tubing, electric cables or flat heaters, heated floors, walls and ceiling conceal their function as heat emitters. There are usually less constrains imposed on furniture placement. There are no air registers or baseboard convectors to be in the way of furnishing and aesthetics.
Many radiant panel heating systems, both hydronic and electric, are designed for room-by-room zoning. This offers energy savings by reducing temperature in unoccupied rooms. It also allows different occupants to adjust rooms to their own desired comfort level. And it helps to prevent localized overheating due to solar or other types of internal heat gain.
In most cases the air motion is so slow that it is not detectable by occupants. Central forced-air systems, by contrast, often create very noticeable whole-building air circulation. The latter tends to distribute dust, odors and airborne viruses throughout the entire building. Some central forced-air systems also pressurize rooms as they operate, increasing air leakage and wasting energy.
The small tubing, electrical cables or flat heaters supplying radiant heating are easily concealed within the building’s structural cavities. By contrast, air ducts of equivalent heat carrying ability often require careful planning and structural alterations if they are to be totally concealed.
Many heat delivery systems, such as forced air and hydronic baseboard, have low thermal mass. This limits the rate of heat output to the heating capacity of their heat source. By contrast, a heated floor slab with its large reservoir of heat can release a burst of heat when needed. An example is when a large overhead door in a garage is opened and cold air floods in across the floor. Comfort conditions are reestablished very quickly after the door is closed.
Quick heat gives an almost instantaneous improvement in the thermal comfort of a cool room. Although the objects and air in the room will require some time to warm, radiant heat loss from the body is reduced within a couple of minutes of turning on the low mass panel.
Dry floors improve safety and provide much better working conditions than wet floors. It is a tremendous benefit in auto service garages, fire stations and other vehicle service facilities.
Panels encased in concrete floors are very resistant to damage from heavy interior traffic. Likewise, heated ceilings are not likely to be damaged by normal building usage.
Properly designed and installed systems eliminate expansion noise, sheet metal vibration, or velocity noises caused by fast moving air. Attention to detail during installation is crucial to achieving a quiet distribution system. An improperly installed radiant system can be very noisy, and silent operation is one of the key benefits of hydronic-based systems.
Low-temperature heat from solar collectors, geothermal heat pumps or waste heat recovery systems can often be utilized for radiant heating. Such heat is only marginally suitable for other types of delivery systems.
Low-voltage electric heating panels may be directly connected to solar panels or wind generators, and line voltage electric panels on the grid may also get their power from solar panels or wind generators.
* Since comfort is maintained at lower air temperatures, the heating load associated with air exchange is reduced. The greater the heating load due to air exchange, whether by natural leakage or forced ventilation, the greater the energy savings.

* Easy room-by-room zoning control allows unoccupied spaces to be reduced in temperature reducing total heating load.

* Eliminating the stack effect inside buildings reduces air leakage.

* Eliminating the layer of warm air normally present against a ceiling’s lower surface reduces conductive heat loss.

* Low water temperatures improve boiler efficiency and reduce heat loss from distribution piping in some hydronic radiant panel systems.

* High thermal mass systems have the potential to make good use of low-cost off-peak electrical utility rates where available.

* The electrical energy consumption of small circulators used in hydronic radiant panel systems is usually of lower than blowers in forced air systems of similar heating capacity.

* Electric radiant panel systems are 100% efficient because all electrical losses go to heat.

Estimates vary as to how much energy a radiant panel heating system saves compared to other methods. It is not uncommon to experience savings of 20% to 30% or more. Many factors influence the extent of energy savings attained by a given system.

Buildings with high ceilings, relatively poor insulation, high air exchange rates or a combination of these characteristic have the potential for greater savings using a radiant panel heating system. Certainly, the quality of design and installation of the radiant panel system will affect the results.

Disadvantages of Radiant Heating

Heated floors are part of the infrastructure of your home, so you have to place the heating panels under the floor. As a result, it’s a system that’s nearly impossible to install on floors already installed. If you have new floors or you like your floors so much you would hate to see them ripped up, radiant floor heating might not work for you.

On the other hand, if you’re building a new home or planning on replacing your floors in the near future, this is the ideal opportunity to consider heated floors. Or, if you can use a crawl space or basement to get under the house, you can also consider electric radiant pads that go in between the joists under the subfloor.
If you experience a significant number of cold days every year, heated floors might sound like a great option for warming your house. However, it doesn’t work as well if you’re trying to cool your house on warm days. Most radiant systems use a cooling machine connected to the tubing to pump cool air through the floor. This can work in dry climates, but when the humidity starts to go up, this type of system can cause issues. First, condensation can form on the floor and cause it to become very slippery. Second, this moisture can also lead to fungus growth inside your house.
The size of the room, the type of floor you have, and what insulation you have installed under the floor all play a role in how long it takes to warm up heated floors. A good insulation can increase the amount of warm air that transfers up through the floors and cut down on the amount of time it takes to warm up the floors.

If you have a small room with wood floors, you can expect your floors to heat up between a half hour to an hour. If you have concrete floors or a large room, it could take anywhere from two to eight hours to get to the desired temperature.
If you’re retrofitting your floors to add radiant heat, unless you’re a seasoned flooring pro–you’ll want to hire a professional contractor to do the job for you. This means the overall cost of the project will be comprised of the product and the labor costs associated with installation. The total product cost itself will vary depending upon how much of the floor and subfloor need to be torn out and reinstalled. The typical cost for a hydronic heating system is around $6-16 a square foot.