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Radiant Heating Systems for Floors and Walls

Radiant heating systems directly heat the floor or panels in the wall or ceiling of a house, rather than heating the air, as do forced-air
heating systems. The radiant heating technique can be likened to standing in full sun on a chilly day, or feeling the warmth of a distant bonfire even though the air is cold. Despite their name, radiant heating systems also depend on convection — the natural circulation of heat within a room — caused by heat rising from the floor.

Radiant heating has been used since ancient times, perhaps as far back as 4000 BC in Mongolia. The ancient Romans, too, made use of a type of radiant heating known as a hypocaust to heat their houses and public baths. Recent decades have seen more mainstream use of radiant heating in Europe, although it is finally gaining popularity in the United States, especially in new-home construction, where installation of radiant heating is more economical.

Radiant heating systems use one of two heating mediums, each of which is described below:

water (hydronic) radiant heat: This system uses hot water carried by tubing, arranged in a grid, to heat the home.
electric radiant floors: This system uses electricity carried by cables or floor mats to heat the home.

An installation of a radiant heating system in a floor is either wet or dry (not to be confused with the aforementioned distinctions), and the decision to use one or the other is largely based on whether the system will be installed in new or existing construction. These two methods are briefly summarized as follows:

In a wet installation, the heating panels are installed on the floor, and a thin layer of concrete or gypsum is spread over the installation, sandwiching the cables or tubing between two layers of flooring or concrete. This installation is ideal in new-home construction, where a concrete slab, which has high thermal mass, is used to build the ground floor.
Radiant floor dry installations are relatively new strategies in which the cables or tubing run in an air space beneath the floor. Tubing is often sandwiched between layers of plywood or beneath the sub-floor. Dry heating is more common in retrofits and when the floors in new homes are not poured concrete.

Advantages of Radiant Heating

efficiency. Radiant heating systems use less energy than convective heating systems where the same fuel is being used. This is due to a number of reasons:
- The thermostat can be set to a lower temperature and still afford the same comfort. Rooms heated by radiance are typically heated uniformly from floor and ceiling, in contrast with forced-air systems, which leave the floors cold. Studies conducted by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) indicate that people can be as comfortable at temperatures 6 to 8 degrees lower with radiant heating than with convective heating that uses air as the primary heat-transfer medium.
- They require no ducts or pipes, which account for heat losses in other systems.
- There is less heat loss through windows because air is not being blown.
- Radiant heaters can be zoned so that energy is only used to heat individual rooms. You can thus more easily direct heat to areas that are more trafficked or chillier, while directing heat away from rooms that see little use.
Radiant heating systems, unlike forced-air systems, pose little threat of spreading dust, pollen and germs.
flexible fuel choices. Hydronic systems can be heated with a wide variety of energy sources, such as solar water heaters or gas, wood or oil-fired boilers.
unobtrusive. Radiant heating systems are not visible in the occupied space, which saves floor space and allows for more decorative freedom.
quiet and clean. Radiant heating systems are quiet, clean and require little or no maintenance. An oil-fired heating boiler, on the other hand, requires annual maintenance.
Radiant heaters take a long time to cool. This can be beneficial in several ways:
- The heater can be run at night during off-peak hours when electricity rates are cheaper. It can then be turned off, yet still radiate heat, during peak hours.
- As it takes a long time for radiant heaters to cool down, they will continue to provide heat for hours into a blackout.

Disadvantages of Radiant Heating

Additional under-slab insulation is required for radiant heating systems mounted on the ceiling.
limited choice of floor covering. Carpet, due to its properties as a thermal insulator, reduces efficiency of in-floor systems. Wood, too, may not be a good choice because of its tendency to crack or shrink when heated. If wood must be used, it is best to use wood with a low moisture level to avoid shrinking and gaps.
potentially high utility costs. In some areas, electricity is the most expensive way to provide heat.
high up-front cost. Due to their complex installation, up-front costs can be prohibitive.
long warm-up period. Electric radiant heating systems heat up faster than liquid systems, although both take longer than conventional forced-air systems.
They can only be used to heat. Separate radiant heating systems are required to provide cooling, air cleaning and ventilation. A forced-air system, by contrast, can do all of these things.
Maintenance and repair of pipes may be difficult due to their lack of accessibility.

FYI, radiant heating is an attractive alternative to conventional heating systems, although neither system is perfect.

Radiant Heating Manufacturers

Window Gas Fills: What Consumers Should Know

Improvements in window design are an important step toward reducing overall energy costs, as heat gain and loss through windows account for up to half of a home’s heating and cooling needs, according to the U.S. Department of Energy.

Gas fills, as well as other efficient or green window features, such as low-E coatings and Heat Mirror® insulating glass, help plug “thermal holes” in the building envelope.

When used in conjunction with low-E coatings, gas-filled window units can yield incredibly high R-values, so they make a good choice for retrofitting a home to enhance its overall energy efficiency. Consumers can educate themselves on the benefits of multi-paned gas-filled windows, and home inspectors who perform energy audits and/or thermal imaging inspections can help their clients determine whether a retrofit with this type of window is a cost-effective upgrade.

What are Window Gas Fills?

Gas fills are special gases pumped inside insulated glass units (double- and triple-paned window assemblies also known as IGUs) to improve their thermal efficiency. These viscous, slow-moving gases (typically, argon and krypton) allow for less convection than would ordinary air, minimizing convective currents within the window and reducing the transfer of heat across the window. Argon Window Gas Fills Homeowners may be able to tell if a building’s windows are gas-filled by checking the specifications on the original work order or the window tag, which is typically found along the bottom inside track of the window. Two small holes may also be observed along the spacer — one where the gas entered the unit and the other for air to exit.

Argon and krypton are the gas fills used most often by window manufacturers to displace the air between the panels in windows. Argon, which comprises slightly less than 1% of the Earth’s atmosphere, is non-toxic, inert, clear and odorless. Its thermal conductivity is roughly 67% that of air and it’s inexpensive, making it an attractive gas fill.

Krypton shares many qualities with its fellow noble gas argon, except that it’s an even better insulator, albeit more expensive to produce. When cost and functionality are considered, argon is a more efficient thermal barrier per dollar spent, especially in the larger ½-inch (11mm to 13mm) gaps between double-paned windows. Krypton is more commonly used in the tighter ¼-inch to 3/8-inch (6mm to 9mm) gaps within triple-paned windows. A mixture of krypton, argon and oxygen gases is sometimes used to reconcile performance and price, and occasionally xenon and nitrogen are used, as well.

Window Gas Leaks

Gas-filled windows will leak over time — as much as 1% per year, according to some estimates — depending on the quality of the window and its installation, the building’s climate, including its exposure to the sun and the altitude, and other factors. However, these windows will usually perform adequately even after many years of gradual depressurization. According to the National Glass Association, if 80% of the gas remains in spite of gradual leakage over time, a window can be expected to maintain its properties and effectiveness. That means that, “even if 1% was leaking out per year, the window would still be effective in 20 years.”

If the breach is significant, however, the window will no longer be an effective thermal barrier and may require replacement. Condensation or fog inside the window unit indicates that the gas fill has escaped and been replaced with moisture-laden air. Homeowners should clean the window’s exterior to be sure that the observed moisture is, in fact, within the window rather than on its surface. The manufacturer or installer should be contacted if the window fails. Leaks can be detected only with special gas-detection equipment. But homeowners should rest assured that leaked argon or krypton poses no health hazards to a home’s occupants.

One rare yet shocking consequence of argon leakage is the sudden implosion of the window. Popped argon window Window Gas Fills Due to molecular differences between argon and the principal components of air, nitrogen and oxygen, argon under pressure to escape a window unit may exit the seal faster than it can be replaced with air. Under this circumstance, the glass will bend inward to accommodate the gradual reduction in pressure within the window. If conditions are right, according to USGlass Magazine, “units have been reported to shatter with a bang, sometimes described as loud as a gunshot. While the broken glass usually stays within the unit, on at least one occasion, glass has shattered with enough force to send glass shards flying outward.” Elevation differences between the location where the IGU was first pressurized and its installation location may also account for the negative pressure. This phenomenon is quite rare, however, especially in newer windows with superior seals.

Double- and triple-paned windows are often filled with the gases argon or krypton to reduce convection within the window units to improve the building’s overall energy efficiency. IGUs can be huge energy-savers for homeowners, and InterNACHI inspectors can help their clients determine whether these windows are the right choice.

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Radiant Heating Systems