The various types of furnaces available differ primarily by the type of fuel they burn — or any other means by which they create heat. There are numerous types of fossil fuel burning furnaces, although the most common burn gas or oil. For alternate fuels, there are furnaces that can utilize wood, coal, or manufactured wood pellets. More and more, you’re seeing solar-powered units, and there are also electric furnaces. In this article, we’ll take a closer look at the most common types of furnaces.
The standard gas furnace is set to burn natural gas (methane), but can be converted to use LP (liquefied petroleum) gas, which in Minnesota is usually propane. Other parts of the world may use butane or a mixture of butane and propane as their LP gas.
Gas-fired furnaces are by far the most common, with natural gas the primary fuel for urban areas and propane the fuel of choice for rural areas. Propane is usually more expensive, but it can be easily liquefied and stored in your backyard. Natural gas is provided through a piping network and stays in a gaseous state for the entire journey through the pipeline and into your home.
Burning natural gas and propane gas is very similar in heat output and temperatures within the furnace, so the efficiencies and the operating characteristics of the furnace are the same. The choice of one or the other is based on personal preference, cost, and availability. After all, if you're in an area without a natural gas pipeline, your only option for gas will be LP.
Fuel Oil Furnaces
Fuel oil furnaces are becoming less popular, primarily due to the higher cost of oil. It burns hotter than gas and requires a special burner to atomize (convert to a mist) the oil, so it’s a completely different furnace that is usually heavier (thicker steel) and constructed differently to handle a different style flame — a sort of “blow torch” flame. Because of these specialized features, oil furnaces also cost more. Most fuel oil furnaces fall in the low 80% efficiency range. It takes a very specialized heat exchanger to make an oil furnace 90% or more efficient.
Last on this list is the simple electric furnace. Simple in that it’s just like your toaster: It has wire coils that heat up the air. It’s 100% efficient as there is no heat lost up the chimney or vent. But electric energy is expensive, so even though it wastes nothing, it may cost considerably more than gas heat.
Some electric utilities offer a very low rate for “off-peak” electrical use, but the power company has the ability to shut off power to your furnace during peak demand periods. Of course, you’d need a backup heat system if you use off-peak power, in case that peak period occurs during subzero temperatures!
What About Boilers?
All of the above also applies to hot water, or hydronic, heat. Boilers are available in gas fueled, oil fueled, and electric versions, with all the same pros and cons. Many new homes with in-floor radiant heat use an electric boiler on off-peak power for a very comfortable primary heating system, with a gas furnace as a backup. Since some sort of a blower or air handler is needed for air conditioning, it’s not that much more expensive to use a gas furnace, and then it doubles as a secondary heating system during peak periods when the power company shuts off the electric boiler.