Integrity Air Conditioning
Posted on January 19, 2020
A gas furnace is designed to heat air and distribute it throughout the house through a ductwork system.
Supply ducts deliver the heated air to different rooms in the house. Return ducts bring cooler air back to the furnace to be reheated.
A gas furnace that’s more than 10 years old can be functioning perfectly but only working at 65% efficiency. With the newest technology available, gas furnaces can operate at over 94% efficiency. This means that by upgrading from a 65% efficient gas furnace to a 96% gas furnace, you’ll drop your gas bill by 31% just by doing that alone!
Furnaces like this can operate reliably for years, but even when they’re operating perfectly, they probably won’t be more than around 80% efficient at turning fuel into heat for your home.
A furnace burns fuel to generate heat and needs to put that heat into an air stream in your ducts, or into the water in your pipes. The efficiency rating is what percentage of that heat gets into your air or water. What happens to the rest of the heat? It goes up the chimney and is lost into the sky. Therefore, a 15-year-old furnace that is 65% efficient is putting 35% of the heat you paid for up the chimney.
A 96% efficient furnace only “wastes” 4%! A big difference! And since the cost of the fuel you put through a furnace, boiler or water heater during its lifetime is much greater than the cost of the unit itself, it’s worth it to install the very highest efficiency equipment available!
Gas furnaces are described in the following ways:
BTU output. The heat output of a furnace is listed in thousands of btus (80,000 btu, for example) and denotes the amount of heat energy the furnace can produce.
Annual Fuel Utilization Efficiency. A standard measure of efficiency for furnaces, AFUE tells you the percentage of input energy the furnace can convert to output energy for warming your home.
Configuration. A “high-boy” furnace is a tall model with the blower located under the heat exchanger. A “low-boy” furnace has the blower in back of the heat exchanger, making it shorter.
Combustion. Both “sealed combustion” and “atmospheric combustion” furnaces are available. Differences between the two types are discussed below.
A sealed-combustion furnace is so named because the combustion chamber is sealed in order to have more control over the combustion process. The air required for combustion is piped to the combustion chamber from outside the house, through a small-diameter plastic pipe. Gasses that result from combustion are also vented outside through a plastic pipe, with assistance from a small fan. This type of furnace is also sometimes called “direct vent” because it can be vented through an exterior wall. No chimney is necessary.
Sealed-combustion furnaces are super-efficient, earning AFUE ratings of 90% or higher. Nearly all the heat potential of the fuel is extracted, making flue gasses cool enough to be passed through a plastic exhaust pipe. A small amount of water results during the heat condensing cycle, and this condensate is typically piped to a floor drain.
A sealed-combustion gas furnace is a smart choice if you are thinking about replacing an old furnace. In addition to cutting your gas bill, this type of furnace will be safer to operate because there’s little danger of back-drafting (which can pull hazardous combustion gasses into your living space).