Understanding How Variable-Speed Furnaces Work and What Benefits They Can Provide

November 14, 2023
furnace installation in Nacogdoches, TX

Are you looking to upgrade or replace the furnace in your home? Whenever the time comes that you need to install a new furnace, we’d definitely recommend that you consider a variable-speed unit. A variable-speed furnace will be the most expensive option, but it’s an investment that can pay off in the long run by greatly reducing your heating costs and providing many other important benefits.

Comparing Standard and Variable-Speed Furnaces

Most gas furnaces are single-stage units, which means they have only one speed or power setting. There are also two-stage furnaces that have two speeds or power settings. A two-stage furnace works exactly like a single-stage unit when running on full power, but it can also partially close the gas valve to run at around 60-70% of its total capacity.

Variable-speed furnaces are often referred to as modulating furnaces, and this is because they have a modulating gas valve that allows them to operate at anywhere from 25% to 100% capacity. The other difference is that this type of furnace operates alongside a variable-speed blower that can speed up or slow down to regulate how much air flows at one time.

How a Variable-Speed Furnace Works

The control board in a variable-speed furnace works in tandem with the thermostat to constantly regulate how much heat is produced. When a variable-speed furnace first turns on, it will always start off with the gas valve only partially open and the blower running at a lower speed. If the temperature in the home is more than 3-5 degrees cooler than the thermostat setting, the control board will signal the gas valve to open further so that the burners produce more heat. At the same time, the blower speed will also slowly increase so that the heat circulates more quickly and the blower brings more cool air into the furnace.

Once the building is fully warm, the furnace will start operating at lower power and the blower will run at a slower speed. The system will then continue running at a much lower capacity, and the control board will constantly regulate how much gas flows and how fast the blower runs based on how much heat is currently needed.

One issue with single-stage furnaces is that the temperature frequently fluctuates as the furnace continually turns on and off. Single-stage furnaces also often don’t run long enough to fully heat every room to the same temperature, which can result in hot and cold spots in different parts of the home.

Variable-speed furnaces will usually run almost constantly throughout the day and night except on warmer days when not much heat is needed. This helps to ensure that every room stays consistently warm and prevents the temperature from fluctuating.

Why Heating Costs Are Much Lower With a Variable-Speed Furnace

A variable-speed furnace will typically run at no more than 50% capacity around 80% of the time. This means that it will use much less energy than a single-stage furnace despite it running almost constantly instead of continually cycling on and off.

When running on lower power, a variable-speed furnace will burn far less gas. The blower also uses much less energy when running at a lower speed. A standard furnace blower usually uses around 400 watts of electricity per hour, whereas a variable-speed blower will only use somewhere around 75 watts per hour on average. On average, a variable-speed furnace can reduce your heating costs by two-thirds compared to using a single-stage unit.

Other Benefits of Installing a Variable-Speed Furnace

Variable-speed furnaces will greatly improve your comfort by maintaining a consistent temperature and preventing cold spots. The fact that a variable-speed unit will run almost constantly also helps to improve indoor air quality since the air in your home will continually circulate through the furnace filter many more times a day.

Variable-speed furnaces also produce far less noise, and some units operate almost completely silently when running on low power. Constantly cycling on and off puts lots of strain on a furnace and leads to increased wear and tear on its components. By running continuously on lower power, variable-speed furnaces experience far less wear and tear. As a result, they tend to have a longer lifespan compared to single-stage furnaces and are also less likely to break down or need expensive repairs.

Nacogdoches Sheet Metal, Plumbing & Air Conditioning, LTD. is the top choice for furnace and AC installation in the Nacogdoches area, and our certified technicians can also help with your heating and AC repair and maintenance needs. For more information on the range of furnaces we offer or if you need any HVAC or plumbing service, give us a call today.