A high efficiency furnace is a heating system that is able to convert the vast majority of its fuel source to energy, with very little lost or wasted. In most cases, the best way to determine efficiency is to look at the annual fuel utilization efficiency (AFUE). However, in addition to this number, there are other factors that go into having a high efficiency furnace.
Most furnaces should meet a minimum standard of 78 percent. However, in order to really be considered a high efficiency furnace, a rating of at least 90 percent is desired. Efficiency of furnaces is usually highest when the heating system is new. For those who find their furnaces literally burn more money year after year, the time may have come for a replacement.
There are two primary ways in which the furnace itself will lose heat, and thus efficiency. It will lose this heat through heated gases and through water vapor, both of which may leave the home through the discharge area, known as the flue. A high efficiency furnace will stop this from happening by at least removing heat from the water vapor through a secondary process and used to heat air going into the home. This capturing of heat will mean less heat loss.
In addition to this heat capture, there are other minor ways that certain types of heaters can be improved. Having an electronic ignition and sealed combustion can also help. These ways will not have as big of an impact in creating a high efficiency furnace, but will add to the total in some small way.
While a high efficiency furnace may cost more than other types of furnaces, there are some definite advantages. The main advantage is that the furnace is not using as much fuel. In fact, over a typical heating season, this type of furnace can reduce the cost of heating as much as 10 to 20 percent. This could quickly make up for any higher acquisition costs. It is estimated that a high efficiency furnace will make up the cost of most price differentials within three years. Also, these furnaces do tend to keep the controlled environment more comfortable overall.
Some homeowners may buy a furnace but then become disappointed that anticipated energy savings are not realized. It is important to remember that a high efficiency furnace is a major component, but only one component, of a heating and environmental system. Rips or holes the in ducts, clogged air filters or vents, will all cause higher energy usage than would normally be the case.