Furnaces
Furnaces use oil, propane, or natural gas as a fuel source to provide heat into a forced-air system. Essentially, the flames heat up the inside surfaces of a heat exchanger while a blower pushes the indoor house air across the heat exchanger to pick up the heat. Furnaces come in a variety of efficiency levels, with some variance depending on fuel type.
Here's a basic breakdown by fuel-type:
- Oil (includes BioFuel Oil): Most of these furnaces max out at ~80% efficiency
- Propane (typically used when natural gas is not available): Older units down to ~70% or less. But, new units up to ~95%.
- Natural Gas: Older units down to ~70% or less. But, new units up to ~95%.
Multi-stage Output
Some propane and natural gas furnaces have multiple stages of heat delivery. This is especially useful when dealing with zones that require little amounts of heat at a time.
Air Temperature
Gas Furnaces have warmer air temperature than do heat pumps. You can expect a delivered air temperature of ~120-140 degrees from a furnace, compared to ~100 degrees from a heat pump. Due to the warmer air temperature, most people find that furnaces create greater comfort. Because the btu output is not dependent on the outside air temperature (like heat pumps), furnaces can also deliver heat faster in cold weather.
