Forced-Air Heating v Boiler Heating

Forced-Air Heating v Boiler Heating

Forced-Air Heating vs. Radiant Boiler Heating

Today, energy-efficient and comfort-conscious consumers have several options when it comes to heating their homes. This wasn’t always the case. But now its best to do quite a bit of homework before you choose a systemwhether its an upgrade  or equipment for a home that youve just built.

Whatever you decide, choose carefully. Both forced-air and radiant boiler heating systems offer long service lives with proper maintenance. You’ll be living with the results, pro and con, of your choice for many years.

Radiant Heating

Radiant boiler heating is more than a 21st century alternative to forced-air heating. While early uses of underfloor radiant heating date back to ancient Rome, even in the United States it has a long history. A Civil War text describes hospital field facilities built in 1864 with radiant floor heating. Visionary American architect Frank Lloyd Wright installed a radiant floor in an iconic design in the 1930s. “There is no other ideal heat,” Wright wrote of his radiant floor system. That system still keeps the house comfortable today.

By definition, a forced-air furnace warms your home by heating the air around you. Radiant energy, on the other hand, just heats you — and other people and objects in the room. It’s like standing next to a window on a winter day with the sunlight streaming in. You’re comfortably warmed by the sun’s radiant heat, even though the air in the room around you remains cool.

In the most common hydronic radiant system, water heated by a high-efficiency boiler to a temperature of around 110 degrees is circulated through loops of tubing integrated in the concrete slab or installed just below the subfloor. Heat energy conducted from the tubes slowly warms the entire floor, which, in turn, gently radiates heat into the room above. People in the room are heated by radiated heat energy and by conduction of heat directly through any objects in contact with the floor—including feet. This method of conveying heat from point A to point B is extremely efficient, compared with forced-air, because warmed air holds less heat energy and loses it faster than water. In comparison, the heat-carrying potential of a cubic foot of water is 2,500 times the potential heat quantity in a cubic foot of air.

Forced-air heating

Circulating hot air through a structure for warmth has a similarly long provenance. Hot air diverted from fires into stone channels was dispersed through Greek and Roman villas in ancient times. More modern furnaces took advantage of the natural convective principals of rising hot air to pipe it from the basement into upper floors through metal conduits. Electricity brought about the development of electrical-powered air blowers in the early 20th century, putting the force into “forced-air.”

In a common gas-fired forced-air heating system, air is pulled out of rooms through return ducts by the suction of the blower fan, heated as it is drawn over the heat exchanger inside the furnace and then distributed through through supply ducts to warm every room in the home.

Benefits of Radiant Boiler Heating

  • Radiant heat warms the room at the level where people live, within a few feet of the floor. Conversely, heated air from a forced-air furnace duct quickly rises up and often out of the room. Typically, the room thermostat for a radiant system can be set up to eight degrees lower than the thermostat for a forced-air system, with no disparity in comfort level. Radiant heat energy benefits people in the living spaces of rooms—not the ceiling.
  • Once the floor is heated to operating temperature, it functions as a thermal mass that continues to emit heat between the on/off cycles of the boiler that heats the circulating water. This effect smoothes out the often abrupt and uncomfortable temperature fluctuations that occur when a forced-air system cycles on and off.
  • Heat energy in hot air transmits readily through glass windows on a cold day. The electromagnetic energy of radiant heat, however, tends to reflect off window glazing and remain indoors.
  • Radiant heat requires no blower or other air circulation to infuse a room with warmth. This draft-free performance reduces the level of dust and other airborne particulates and makes indoor air less likely to trigger allergic responses in susceptible individuals.
  • Forced-Air Heating v Boiler Heating
  • The noise of air rumbling through ductwork is one of the hallmarks of a forced-air furnace. A radiant system is completely silent.

Disadvantages of Radiant Boiler Heating

Because a forced-air furnace uses installed ductwork, that same duct system can be used to disperse cooled air in a central air conditioning system during the summer. In homes where radiant heat is installed, however, other cooling alternatives such as the ductless mini-split  or window units must be used.

The cost of installing radiant heat requires careful consideration, particularly when the system is a retrofit. But if the retrofit involves removing the existing floor anyway, the price of adding radiant tubes below the replacement floor is competitive with the cost of retrofitting ducts for a forced-air system. Take care to locate and vet a qualified contractor with  expertise in installing a radiant boiler heating system. Not every contractor with forced-air experience is qualified to properly size and install radiant heat.

A radiant system requires some expectation adjustments, particularly when it comes to demands for quick heating. While a forced-air furnace can flood a room with hot air relatively quickly, a radiant system takes time to warm the floor fully and emit enough energy to make occupants comfortable, especially if the thermostat has been set very low overnight. Proper use of a programmable thermostat can minimize these time lags.

Selecting appropriate floor coverings for a radiant floor requires consideration. Materials that insulate the floor from the room, such as thick carpet, are not appropriate. Carpeting made for radiant flooring is available, however, and most forms of tile and other conventional coverings emit radiant heat.

Benefits of Forced-Air Heating

  • Because forced-air heating predominates in residential applications, the mass production of furnaces and ductwork, as well as the fine-tuning of installation practices, have lowered the upfront costs of using this heat source. In most cases, installing forced-air heat is the most economical option.
  • Ductwork used to convey heat throughout the home in the winter can also be used to convey central air conditioning in the summer. Todays central heating furnaces often include an A/C evaporator coil and condensation collection equipment that can be incorporated into a central air conditioning system. Consolidating both systems is space-saving and cost-efficient.
  • Forced-air heating and cooling systems are often the front line of defense for maintaining healthy indoor-air quality. Because these units circulate air through a filter. the air in the home is filtered several times each day. The whole-house air circulation of a forced-air system can also be treated by a humidifier .

Disadvantages of Forced-Air Heating

Moving hot air is a complex way to convey heat energy from its source to diverse rooms in a house. Large volumes of heated air may escape from ductwork before it reaches its destination, or the heat energy may be lost because of thermal transfer that occurs when ducts are routed through cold unconditioned zones, such as attics or crawl spaces. On average, up to 20 percent of the heat produced by a forced-air furnace is lost. In older houses, this loss can be even more significant. The loss can only be made up by longer furnace on” cycles that consume more natural gas and boost operating costs

The natural process of convection—hot air rising—means layers of hot air stratify at the ceiling of a room heated by a forced-air furnace. This heat offers little warming effect at the floor level, where people reside. It is also readily lost into the unconditioned attic unless adequate insulation and careful air sealing is maintained.

A forced-air system is designed to maintain a delicate balance between air entering a room through the supply vents versus air leaving the room through returns. This preserves a condition of neutral air pressure in each room, a must for proper heating and cooling, as well as healthy air quality. When this balance is tipped by an excess or shortfall in either supply or return air volume—a frequent consequence of common duct leakage—room comfort, system efficiency and interior air quality are diminished.

For more information about the pros and cons of forced-air heating vs. radiant boiler heating, contact Riley Heating & Cooling  in Oak Park.


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