Furnaces, Filters & HeatersMore about Furnaces, Filters & HeatersNatural gas furnaces
Energy efficient furnaces are classified by Annual Fuel Utilization Efficiency (AFUE) ratings according to the percentage of generated heat that is transferred from the furnace to the home (the excess escapes through the flu). The national minimum standard is 78%, with ENERGY STAR qualified models falling between 85-95%. Furnace performance is contingent upon this rating, but arguably even more affected by installation, maintenance, and product quality. Depending on how much heating you need and how long you plan to live in your home, investing in a higher efficiency furnace may be cost effective. Fuel Oil furnaces
Electric Furnaces
Corn & Wood Pellet Furnaces
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Most natural gas furnaces contain the same basic parts: a gas burner (where the fuel is burned), an ignition device to light the flame, heat exchangers that transfer the heat from the combustion gases to the home, a blower to circulate air into and out of the home, and an induction blower to remove the exhaust gases via the flue. Today’s furnaces are capable of capturing more of the heat produced by combustion. Additional heat exchangers and other technologies remove more heat from the gases, indicated by the lowered temperature (and in some cases condensation) of the exhaust gases. “Pulse combustion” is another system of contained burning that raises efficiency to 93% and requires minimal electricity.
Oil furnaces are very similar to gas furnaces; the most significant difference lies in the firing apparatus. Instead of merely burning the fuel, oil furnaces utilize a high-pressure burner to atomize the oil before mixing it with air. Otherwise, the technology (and therefore efficiency) is very similar. Fuel oil is similar to diesel fuel or kerosene, and therefore is dirtier and less environmentally-friendly than natural gas or propane. Because of this, an annual maintenance or service visit is highly recommended.
Electric furnaces are very efficient; they utilize an electric resistance heating coil that simply converts electricity to heat inside of a cabinet and is circulated by a blower. The issue with electric furnaces is the intrinsic problem with electricity as a heat source. Another type of fuel (often coal), is burned to generate the electricity. This is the exact process that occurs in other types of furnaces, meaning that the extra step of resistance heating must be 100% efficient to compete evenly.
These eco-friendly furnaces permit the owner to be virtually independent of fossil fuels—a tantalizing proposition given the volatility of their prices. Wood pellets (made from compressed sawdust) and corn kernels can be burned in furnaces that resemble a traditional unit, but integrate a large “hopper” to store the fuel. A series of augers transfer the fuel into the combustion chamber, beyond which point the technology is exactly the same as a gas- or oil-fueled furnace. This solution is ideal for rural customers with access to the fuel and a place to store it between deliveries. Although the upfront costs are higher, the payback may be great in the context of an increasingly oil-hungry world.