Types of Furnaces
Which furnace did you need?
There are many types of furnaces available to provide warmth and comfort in your home. Before you pick up the phone book and order a furnace however, you'll want to know what it is that you're asking for. Depending on your location, climate, and personal preferences, you will be able to choose between several options to keep your family warm and comfortable.
All furnaces use some kind of fuel to produce and move around heat - usually natural gas, fuel oil, propane, or less commonly a solid fuel like wood or corn pellets. Many of these furnaces actually use two types of fuel - one for the heat itself and another to move the heat around. For example a natural gas furnace burns gas to provide heat for your home, while an oil-fired furnace burns home heating oil. In either of these cases, the furnace also uses electricity to power a fan or blower, which is used to move the heat around your house, ensuring even and regular warmth throughout the building.
There are a few numbers, ratings, and acronyms that you'll want to familiarize yourself with before looking at furnaces online. Furnaces are generally rated in either British Thermal Units (BTUs) or in Watts / Kilowatts (W / kW). These are two ways of expressing the same thing - the amount of heat energy the unit can produce in one hour.
One BTU is the amount of heat energy needed to raise one pound of water by one degree Fahrenheit at sea level. It's also approximately the amount of energy found in a match. For the sake of comparison, 1,000 Watts (W) = 1 Kilowatt (kW) = 3,413 BTUs. You don't have to remember those numbers, it's just important to know what they represent.
If all of these numbers seem daunting and you just want to know how much money you could save with a different type of furnace, take a look at the nameplate on your existing furnace and compare that to the new furnaces on the market. For instance, upgrading from a 60% efficient furnace to a 90% efficient unit could actually reduce your energy use by half!
There are also several types of efficiency ratings on most furnaces - steady-state efficiency rating and Annual Fuel Utilization Efficiency (AFUE) or seasonal fuel efficiency (SFE).
Steady-state efficiency is generally used by the manufacturers and contractors - it represents the amount of heat energy the furnace generates from your fuel each hour, when it is warmed up and operating at its peak. However, since the furnace will cycle on and off and be used differently depending on the heating season, this number isn't as useful as the SFE or AFUE.
The Seasonal Fuel Efficiency and Annual Fuel Utilization Efficiency ratings are basically the same thing. Each one tells you how well the furnace does at converting fuel to energy through the entire heating season or the entire year.