A residential furnace is an appliance that is permanently installed either inside or outside of a residence and provides heat. Air is heated inside the furnace and it is then forced through ducts and transported throughout the house.
Condensing vs Non-Condensing Heaters
Condensing furnaces are considered “high-efficiency” and come with the highest AFUE rating, while their non-condensing counterparts are rated as “medium-efficiency”. The difference between the two is in the exchanger technology used in extracting heat from the combustion process and the manner in which combustion gases are exhausted. The heat extraction process is more efficient in condensing furnaces because they use two heat exchangers, one for the primary combustion process and another convert the exhaust gases into heat. In contrast, conventional, or non-condensing, furnaces only use one heat exchanger and quickly exhaust combustion gases, rather than converting them.
Types of Furnaces
There are three different ways for furnaces to output heat. Some places, like Goodman furnaces, sell all three, so they are quite easy to find.
A single-stage furnace outputs heat at one speed—high. It cannot be altered to suit the current temperature or specific areas of your home. There is an “off” and an “on” switch and that is it. They are very simple to use, but can drive up energy bills due to the inability to modulate the heat output.
Two-stage furnaces operate at two different speeds allowing users to choose between the maximum output capabilities of the furnace and a reduced amount for when the temperature is chilly, but not freezing. Two-stage furnaces are quieter than their one-stage counterparts and are more efficient.
Variable Speed Furnace
In this type of furnace, the fan motor is made to spin at different speeds in order to control the amount of heated air being sent into the home. Variable speed furnaces also have a bonus—they can be used even when the heat is not turn on, allowing the owner to continually circulate and filter the air in their home. These furnaces often cost more upfront, but are much more efficient and intelligent than the other two types, which will save money in the future.
There are three types of fuel that can be used with furnaces:
Gas furnace as well as those that use liquid propane are most popular in chillier climates, particularly in those areas where natural gas services are available. They are typically efficient, clean, and inexpensive.
Oil usage is slowly giving way to furnaces that use gas, but for a long time, it was the dominant fuel source for furnaces. Oil may still be used in locations where there are no pipelines for natural gas, but it is considered a dirtier heating alternative.
Furnaces that run on electricity are reliable and dependable, given the ready availability of the fuel source. However, electric heaters and furnaces are only economically sound choices in warmer areas, where heat is rarely used or in places where it is used as a backup to another heating source.
A furnace’s efficiency is measured by its AFUE, or annual fuel utilization efficiency, which is the ratio of the furnace’s annual heat output to the annual fossil fuel energy used by the furnace. All new furnaces are required to have their AFUE displayed, so as to allow buyers to compare efficiency between different models. Since 1992, the minimum AFUE for new furnaces has been 78%, but in 2015, that number will rise to 80%, as per the stipulation of a 2007 AFUE standard.