Comparing Forced-Air Heating to Radiant Options
The choice between forced-air heating and radiant heating is not a new phenomenon. In one way or another, and at different times in human history, people have had a similar choice to make when deciding how to make a structure warm and livable. Today, of course, we have other concerns besides simply survival during a cold winter. Comfort, energy-efficiency and safety are major issues when choosing a heating method for a home. Likewise, the economics of installation and the expected service life of the equipment also play a part. Interior heating poses one central question: Do I heat the air itself or heat another medium (such as water) and convey that substance through the house? Forced-air heating and radiant heating each answer that question in different ways, each with its own pros and cons.
What is a Forced Air Furnace?
Heating air to warm an enclosed space dates back to the first fire built in a cave. When applied to more modern structures, however, ancient Romans utilized stone air conduits to move heated air from a central fire to the rooms of a villa, relying on the natural convection principle of heat to distribute the warm air. Forced-air heating was not particularly forceful and limited to passive methods—hot air slowly rising through metal pipes under its own convective force—up until the late 19th century. The development of electric blower motors to “force” air through ductwork, brought about the basic system we all recognize today: A central furnace heating air with a burner flame or electrical resistance coils and a motorized blower fan. A forced-air system is a closed loop. The blower fan continuously draws cooled air out of rooms through the return ducts, reheats the air at the burner, then pushes the hot air through the supply ductwork to all living spaces.
What is Radiant Heating?
Radiant heating also has ancient origins. Greeks and Romans warmed residences with underfloor fires that heated the stone or marble floor, which in turn heated people and objects in the room. However, it wasn’t until the 1930s when famed architect Frank Lloyd Wright saw a Korean underfloor heating system installed in a Japanese home that radiant heating began to be popularized in the U.S. Wright advanced the concept by using circulating hot water as the heat-carrying medium and installed pipes beneath the floors to heat some of his iconic structures of the 1940s. Today, a radiant heating system incorporates a boiler to heat water and pumps to circulate it through a network of narrow plastic tubes embedded in the concrete slab or installed beneath wood sub-flooring. Heat rising warm rooms from the floor up. Some systems use a grid of electrical resistance wires that generate warmth instead of tubing carrying heated water.
Radiant Heat vs Forced Air
Forced-air has become the standard for heating multi-room residences and the widespread adoption of this heat source is in itself one of its advantages. Standardization of furnaces and blowers, as well as ductwork fabrication and duct installation methods, have reduced costs to the point where installing a forced-air system at original construction is often the least expensive home comfort option.
In addition, these other factors favor forced-air:
- Because ductwork is installed to accommodate forced-air heating, the same ductwork can be utilized to provide central air conditioning in summer, as well. Combination central furnace/air conditioning units are widely available that integrate both a standard furnace burner and plenum with an air conditioning evaporator coil for cooling. Both systems utilize the same blower for air circulation and push heated or cooled air through the same network of ducts. Consolidation of all-season comfort functions into a single system is very cost-efficient.
- A function of any home comfort system is maintenance of healthy indoor air quality on a whole-house scale. A forced-air system builds that capability in, as well. Because the system circulates air through the ductwork, a standard or enhanced air filter installed in the ducts removes airborne particulates. The entire air volume of your home moves through the ducts of a forced-air furnace or central A/C multiple times each day, offering continuous air filtration and interior air quality improvement.
- A heating/cooling system that utilizes forced-air also provides opportunities for installing a whole-house humidifier in the ductwork to maintain proper interior humidity.
Forced-air system disadvantages:
- Any occupied structure inevitably has air exchange with the outdoors through leakage or simply through the routine opening of doors and windows. When heat for the home is provided by moving hot air, cold outdoor air exchange infiltrating the home offsets the heating action of the furnace, a continuous tug of war that extends furnace “on” cycles and increasing operating costs.
- Hot air rises. In homes with forced-air heating systems, layers of over-heated air typically form at the ceiling and contribute little to warming the room at lower levels where occupants are. This represents wasted energy and, every time the furnace blower cycles “off,” causes the room to cool swiftly as more warm air stratifies at the ceiling. Also, attic insulation methods must be extensive to minimize loss of heat energy concentrated at the ceiling.
- Forced air systems require careful maintenance of neutral air balance in all rooms. The volume of heated air entering the room must always equal the amount of air drawn out of the room through the returns. When leaks in ductwork or other factors cause an air imbalance, heated air may be pushed out of the room through cracks and gaps in the structure or cold outdoor air may be drawn in. Both positive and negative air pressure in rooms raises heating costs and diminishes comfort level and air quality.
- Budget restraints raise the question of how much is a forced-air furnace? Incorporating a system into a new home is competitively priced. However in an existing house, ductwork can be very expensive to install as a retrofit.
Heat produced by a radiant source can be compared to sunlight warming you on a chilly day. No heated air is rushing around you nor is any required. Your body is simply passively absorbing heat radiated from a distant source. Radiant heating is the most basic method of spreading heat energy and more fundamental than heating air. Hydronic radiant systems utilize water to convey the heat energy from the boiler to the room. Water holds heat much more efficiently than air. A cubic foot of water has 2500 times more potential heat-carrying capacity than a cubic foot of air.
Here are some other pluses of a radiant system:
- Radiant heaters warm the room from the floor up. Gentle heat rising from the floor warms occupants in two ways: by conduction—heat transferring from the warmed floor directly into persons and objects in contact with the floor, and by infrared radiation that warms people, not air.
- Heat from a radiant floor remains closer to floor level and warms occupants where they actually live. Heat energy is not wasted by collecting at the ceiling and less loss of heat occurs into the attic. Radiant systems lose up to 25 percent less heat this way. In addition, the wavelengths of infrared heat energy produced by a radiant system tend to reflect off window glazing and stay inside the house, rather than conducting through the glass. When properly designed, a radiant system can reduce heating energy consumption by up to 50 percent.
- Once a radiant floor is warmed, it acts as a thermal mass that holds heat and continuously emanates warmth between on/off cycles of the boiler. This evens out the often drastic temperature swings of a forced-air system as the burner and blower cycle on and off and air in room quickly loses heat.
- Because a radiant system produces silent, draftless heat, dust and other allergens are not stirred up by circulating air and/or conveyed through ducts to adjoining spaces in the house.
Radiant heating disadvantages:
- Because a radiant system utilizes no ductwork, in order to have the benefits of central air in summer, dedicated ductwork must be installed.
- Upfront installation costs of a radiant system are meaningful, particularly in an existing home as a retrofit. In addition, not every heating/cooling contractor qualified to install a forced-air furnace is experienced with the very different technology of radiant systems.
- Not every floor covering is appropriate for a radiant floor. Any covering that insulates the floor from the room—such as conventional thick carpet—cannot be used. However, thin carpet designed for radiant flooring is available and many forms of tile are also acceptable.
- The time-lag between starting a radiant system with a cold floor and achieving the desired level of warmth in a room is longer than a forced-air system. Homeowners who frequently require instant heat to warm a cold house quickly may find the wait uncomfortable.
For more information about comparing forced air heating to radiant heating, contact us at Black Diamond Plumbing & Mechanical.
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