A furnace is a heater that distributes warm air throughout your home. Though every model follows more or less the same blueprint, its efficiency varies significantly depending on the type you own and the fuel it consumes.
How a Furnace Works
Most furnaces contain six essential parts: a gas valve, an ignition switch, burners, an induced draft motor, a heat exchanger, and a blower fan. These are connected to the thermostat, on one end, and your ventilation ducts, on the other. When the air temperature drops below the level set on the thermostat, the thermostat sends a signal, activating the furnace.
As soon as the furnace has powered up, it opens the gas valve. The flowing gas triggers the ignition switch, which ignites the burners. (Older systems use a pilot light for the same purpose.) Once the flames are lit, the induced draft motor pulls them into the heat exchanger, warming it up. At the same time, the blower fan draws in cold air and forces it up through the heat exchanger. As the air passes over the coils, its temperature rises before it’s blown through the ventilation ducts and out into your home.
Types of Furnaces
Furnaces are classified according to speed ‒ how fast they move air through your house. Your fan speed is one of the factors that affect its Annual Fuel Utilization Efficiency (AFUE), though in this case, faster is not always better. In fact, furnaces that can run at low speeds heat homes far more efficiently.
- Single-stage. Single-stage furnaces can only run at full blast. They generally have the lowest AFUE, around 80 percent, which means 20 percent of the energy they consume is burned away before it can heat your house.
- Two-stage. Valves on two-stage furnaces have three settings: closed, open, and partially open. When the valve is closed, the furnace is off. When the valve is open, it runs full blast. But when the valve is partially opened, it runs at a low speed. This flexibility not only reduces wear and tear but saves energy on mild days when your home only requires a small amount of heat. Two-stage furnaces have an AFUE of around 90 percent.
- Variable Speed. Variable-speed furnaces burn fuel incrementally. Instead of low speed or high speed, you get more options in between. By modulating fuel output, they have an easier time maintaining a consistent temperature in your home and some of the highest AFUE ratings on the market.
Types of Fuel
The other major factor that affects your furnace’s AFUE rating is the fuel used to power it. Not every fuel burns cleanly. Some don’t burn at all. Generally, the fewer byproducts it produces, the more efficiently it heats your home.
- Oil. These types of furnaces draw oil from an underground tank and convert it into a spray for the burners. Burning oil is less efficient than most other fuels except coal, so oil furnaces that still exist are slowly being phased out.
- Natural Gas. Not only the cleanest fossil fuel but also one of the cheapest and most efficient, which is why it’s used to heat more homes than any other fuel in America.
- Propane. Contains more energy than natural gas (2,516 BTUs vs. 1,030 per cubic foot), but costs more to purchase. Consult a local heating expert to determine whether this type of system makes sense in your home.
- Electricity. The most efficient fuel source, with a near 100 percent AFUE rating. Instead of a burner, electric systems blow air over a heating coil before distributing it through your home. However, the rising price of electricity may mwhat is a furnaceake it impractical for some parts of the U.S.
What is a Furnace Protection Plan?
Every furnace, no matter how it’s fueled or how it runs, experiences wear and tear. While some last longer than others, they all fail eventually. Make sure you’re protected from a sudden and expensive breakdown with a HomesentialTM warranty. We cover your home’s essential systems (heating, cooling, and electric), ensuring worn-out parts get repaired and replaced quickly, with no service fees or deductibles. You pay only a low monthly premium while receiving peace of mind, backed by our 24/7 service team. Contact us today and find out how much you can save!