What Is a Modulating Furnace?

Furnaces need to cycle on and off depending on the heating needs of the home. This cycling on and off can waste energy, so engineers have developed a furnace that can operate at different capacities to save energy. Modulating furnaces make slight adjustments depending on the circumstances of the home using a gas valve.


The gas valve on a modulating furnace works in combination with the variable speed blower. These blowers ensure that you feel the maximum comfort. With adjustments made by the variable speed blower, the modulating furnace achieves maximum efficiency while also stopping temperature fluctuations. The modulating furnace operates quietly, can provide a consistent indoor temperature, and keeps the fuel efficiency at 94 percent.


The modulating furnace has an integrated control module motor, which achieves greater energy efficiency than the multi-speed blower. The furnace has 12 different capacities, starting at 40 percent and increasing by 5 percent all the way to 100 percent. These capacities affect how much fuel the furnace burns. The thermostat and the remote control sensors affect the capacity at which the furnace operates. When the furnace first cycles on, it operates at the highest capacity and then slowly reduces the capacity while increasing the blower speed until the furnace reaches the maximum efficiency. Since the unit doesn't cycle on and off, but instead remains at the most ideal capacity, the furnace doesn't waste energy.


You can add a variety of features to the modulating furnace. Furnaces tend to dry out the air, so you can have humidifiers installed on them to keep the air moist. Air filters purify the air to increase the air quality. Choose the size of the furnace blowers, from single zone to multi-zone furnaces. Most importantly, you can choose the highest furnace burning capacity, which can reach 120,000 British thermal units per hour and goes as low as 60,000 Btu/hour. Furnace installation specialists should estimate the furnace capacity that the home needs, since furnaces with insufficient heating capacities will have to keep cycling to maintain the temperature, but furnaces with excessive heating capacities will be a waste of money. Modulating furnaces cost far more than less complex furnaces but save you money over time with your gas bill.

Hassle Free

Modulating furnaces last a long time due to rarely operating at full capacity. They usually come with a five-year warranty. The modulating furnace also makes less noise than older furnaces. Almost anyone can operate a modulating furnace and it relies on a simple thermostat.


Install modulating furnaces in tight spaces. The ducts need to be properly sized so that they run efficiently. The mechanical contractor who installs this furnace should be certified in this specific type of furnace. This furnace works only with propane and natural gas.

About the Author

Charles Pearson has written as a freelancer since 2009. He has a B.S. in literature from Purdue University Calumet and is currently working on his M.A. He has written the ebooks "Karate You Can Teach Your Kids," "Macadamia Growing Handout" and "The Raw Food Diet."