Which Is Better: a Single- or a Two-Stage Furnace?

Single-stage

• A single-stage furnace is either on or off. It does not vary or modulate its motor speed and the airflow. It is also referred to as a constant-speed furnace. Unlike a two-stage furnace, which selects either its stage-one 50,000-BTU capacity or its 100,000-BTU stage-two capacity, a single-stage furnace has no choice. It will always use its "full blast" 100,000 BTU-capacity. If the thermostat is set at 70 degrees Fahrenheit, a single-stage furnace motor will blow warm air at the same rate of speed until the room temperature reaches 70 degrees F.

Two-stage

• A two-stage furnace is one that delivers heat at two different airflow settings, based on the speed of the motor. It is also referred to as a variable-speed furnace. During stage one, the motor is operating at half its potential, and blowing air at a medium or low rate of speed. During stage two, the motor is operating at its full potential. For example, if the furnace has a 100,000-BTU capacity, it will only use 50,000 BTUs during stage one, and all of its 100,000-BTU capacity when it switches to stage two.

Best Choice for Mild Climates

• If you live in a mild climate, a single-stage furnace may be all you need. A single-stage works fine for heating homes in states such as Georgia and Texas, where winters are short, and temperatures fluctuate, with a few days of mild daytime temperatures in between cold days. What you really want is a furnace that can kick in and turn on to knock off the chill in the morning, and keep you warm and toasty at night. A single-stage furnace is a good choice to meet your needs for the three or four months when you want to keep your home warm and comfortable. You will know that the furnace will stay on, working with all its might to keep your home's indoor temperature at whatever you have set on the thermostat, and once the temperature is reached, it will shut off --- and so will your use of natural gas, propane, oil or electricity for heating.

Best Choice for Cold Climates

• A two-stage furnace is good for people who live in cold climates, such as areas of the Midwest and Northeast. A two-stage furnace will keep the home consistently warm and will utilize energy more efficiently. For example, if the thermostat is set to 70 degrees Fahrenheit and it is 20 degrees F outdoors, a two-stage furnace might start off in stage two to get the room warm, then switch over to stage one as rooms start approaching 60 degrees, and keep operating in stage one. As a result, the furnace uses energy more efficiently by only using its maximum capacity when required, without sacrificing heat and comfort.