Whether you choose an 80% AFUE furnace or a 90% Plus AFUE furnace, you will have three different furnace options in that category. You will have to choose between the Single Stage, Two Stage or Variable Speed.
The Single Stage furnace is the traditional furnace design of the past. In the past the Single Stage furnace was the only option. When the thermostat calls for heat, the furnace comes on (full power) until the thermostat reaches the set temperature. Example: If you have a 100,000 BTU single stage furnace. It will come on and run at 100,000 BTU’s until the thermostat is satisfied. Having a single stage furnace is like having a stove with only two settings – OFF & HI HEAT.
The Two Stage furnace has a couple nice benefits. It has two different heat outputs (Half Power Heat and Full Power Heat), depending on what the thermostat tells the furnace it needs. The thermostat will base that decision on the temperature of the house. Example: If you have a 100,000 BTU two stage furnace. First stage will come on (50,000 BTU’s) first. On mild days it will heat your home on first stage without a problem. If it cannot satisfy the thermostat, the thermostat will tell the furnace to activate the second stage (100,000 BTU’s). For a very large portion of the year a two stage furnace will heat your home without ever needing to ramp up to second stage. When it’s running in first stage it’s using about half the gas, but only putting out about half the heat. The Two Stage furnace will run for a longer period of time than the Single Stage furnace, but the longer a furnace runs the more evenly it will mix the air in the home. If you experience uneven temperatures (hot and cold rooms) in your home during the heating season, the Two Stage furnace should help or even eliminate this problem.
The Variable Speed furnace has several benefits. It is often referred to as the Cadillac of furnaces, because of the comfort it delivers. To start, the Variable Speed furnace has two stages like the above furnace. So, you can expect the benefits that come with the two stage furnace, along with everything the Variable Speed offers. The thing that makes the Variable Speed furnace so much better than the others is the blower motor. Your blower motor runs during the heating mode, it runs during the cooling mode, and if you run the thermostat fan switch in the on position (which I highly recommend) – your fan is running 24/7/365. Needless to say, the fan is one of the most important parts of the furnace to consider. Single Stage and Two Stage furnaces have one set fan speed for heating and one set fan speed for cooling. Whether that setting is too high or too low for your duct system, that’s what that furnace will put out. The blower motor on a variable speed furnace has no set speeds. It adjusts itself to your duct system. It constantly measures the pressure in your duct system and adjusts itself so that you always have the correct amount of airflow. This motor runs off a different voltage (DC voltage). Because of the technology, it costs MUCH less to operate than all other motors. Variable Speed furnaces are the quietest furnaces you can buy, they’re the most efficient furnaces you can buy, they clean the air better than any other furnace you can buy, and most air conditioners are rated about 1 SEER more efficient when combined with the Variable Speed furnace.