The difference between an 80% and 90% furnace

Getting a new furnace can be a difficult and annoying experience or a smooth and simple one depending on how much knowledge you have about this topic. Typically, there are several things you need to take into consideration when buying a new furnace. The most common of these is furnace size, but energy efficiency is also very important. Your furnace’s energy efficiency refers to the amount of energy it uses to heat your home and how much of it is wasted.

Energy efficiency can be measured in several different ways but the standard is the Annual Fuel Utilization Efficiency (AFUE) percentage. A furnace with 80% AFUE will use 80% of its energy on heating the home and waste 20%, while furnace with a 90% AFUE or higher will only waste 10% energy or even less with some high-end models. Older furnaces and furnaces that are set up in vented areas typically have a lower AFUE % than their more modern counterparts. Newer furnaces typically have a higher AFUE but, due to the ways these furnaces are usually built, require being installed in an enclosed space.

The major differences between a furnace that has a lower energy efficiency percentage versus one that is higher, other than the amount of energy being used to heat your home, is the type of furnace it is. Furnaces with lower energy efficiency usually employ atmospheric combustion, which means that the furnaces draws in air from the home. Furnaces that operate at higher efficiency draw in air from the outside, through a pipe or tube that is installed particularly to serve this function. This is called sealed combustion, since air intake is sealed off from the inside of your home. Installing a 90% AFUE furnace requires having a room dedicated to the furnace and/or a valve connecting the furnace to the outside air.

High efficiency furnaces also have the distinct advantage of providing various modes of operation, such as variable-speed and multi-stage burning. Variable-speed blowers refer to the speed at which your furnace will be operating, which can vary depending on your thermostat settings or the outside temperature. On cool, fall days where the cold is not too extreme, for example, these types of furnaces will operate on a lower speed thus increasing your monthly savings. Some furnaces also have multi-stage burners, which adjust furnace output, again depending on particular external conditions. Variable speed blowers and multi-stage burners both serve the function of operating at a fraction of the speed and power than is typically possible with the furnace in order to operate at quieter noise levels and provide better heating with less energy.

Lastly, because the air being pulled from higher efficiency furnaces comes from the outside, 90%+ AFUE furnaces will improve the humidity of your home. Since furnaces that operate at lower efficiency are pulling in air from inside your home, after a few hours of use the room can feel dry and stuffy because of all the air has gone through the furnace. With furnaces that use sealed combustion however, the air that is being used to heat your home is always crisp and clean, pulled from outside. If you have the money and your home is suited for this type of furnace, consider getting one that operates at 90% efficiency or higher. The savings on your monthly bill will be well worth the cost.