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What is a modulating furnace?

Washington Energy | 09/25/2010 | Posted in Furnace

What is a modulating furnace and why would I want one?

Did you ever notice that when your furnace reaches its set temperature and shuts off, there are pockets in the room that are still cold? Pretty soon, you’re pulling the throw over you until the heat snaps back on again. A modulating furnace can counter that and stabilize the comfort and heat you feel.

The National Association of Homebuilders likens a standard furnace to stop & go traffic, with its inefficient use of energy for your car and frustration for you. Modulating furnace performance is more like highway driving, where you are cruising along, making slight operating adjustments while achieving maximum efficiency. The modulating furnace operates with finesse to reduce temperature fluctuations, providing consistent indoor temperature, quiet operation, and an annual fuel utilization efficiency (AFUE) up to 98%. That means fuel is used more efficiently, reducing your energy cost. Plus, the home can be more easily and efficiently kept in the perfect comfort zone.

Furnace Temperature Swings

Typically this type of gas furnace, such as Bryant’s Evolution series, combines a modulating gas valve with a variable-speed blower. The furnace then adjusts automatically between 35% and 100% of total capacity, in small increments, continuously regulating the amount of fuel burned according to the thermostat setting. This maintains the temperature to within a ½ degree of your thermostat’s set point. For comparison, you might experience a 6-10 degree swing in temperature vs set point between the cycles of a standard furnace.

The heating mode starts with the gas at 100% and the fan at 0%, the valve reducing and the blower increasing until maximum efficiency is reached. The fan then runs continuously, ramping up or down depending upon air delivery requirements. Since the fan and burner almost never run at full capacity and energy-robbing on/off cycling is eliminated, the unit is highly fuel-efficient.

High efficiency modulating furnaces might qualify for federal energy tax credits. Ask your Home Energy Specialist for more details. Schedule a free estimate today if you’re tired of wasting energy and being uncomfortable.

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2 Responses to “What is a modulating furnace?”

  • Theven

    Question: modulating furnace, should you adjust the temperature when you go to sleep or just have it at a set temperature throughout the night example 70 degrees? Thank you

  • Rick Samara

    Thanks for this great article on modulating gas furnaces. Easy and simple to read, it provides the novice with a great understanding of modulating gas furnaces.


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