Gas Furnaces

What Is a Gas Furnace and How Does It Work?

A gas furnace is the heating powerhouse of a traditional central heating and cooling system. Unlike a heat pump, which moves existing heat from the outdoor air into your home, a gas furnace burns fuel (natural gas or propane) to create heat, then pushes that warm air through your home.

When your thermostat calls for heat, three things happen inside the furnace:

What Is AFUE and Why Does It Matter?

Just like a vehicle uses MPG to measure fuel efficiency, a gas furnace uses AFUE (Annual Fuel Utilization Efficiency). This percentage tells you how much of the gas you buy turns into usable heat for your home versus how much is wasted as exhaust.

Furnace efficiency has come a long way. Many furnaces from 1990 or earlier run at 65% AFUE or less, so replacing an old, low-efficiency model with a modern high-efficiency unit can dramatically reduce your heating operating costs.

Minimum efficiency requirements in the U.S. reflect climate. Because a furnace runs longer and works harder through a cold winter, the minimum AFUE allowed is higher in northern states than in the warmer regions to the south:

• North: 90% AFUE minimum
• Southeast: 80% AFUE minimum
• Southwest: 80% AFUE minimum

Modern furnaces span that whole range, from 80% AFUE up to a very efficient 98%+, and the Muse Heating & Air Conditioning team can help you find the right furnace for your home. Depending on how much you run your system, a higher rating can significantly lower your gas bill. Here's how the two main efficiency levels compare:

Single-Stage vs. Two-Stage vs. Modulating Gas Valves

If you're considering a full furnace replacement, you'll want to better understand your options and their associated costs. Often the options fluctuate between upfront costs vs. long-term savings and performance.

In furnaces, the gas valve controls how much fuel reaches the burners and this, in turn, directly affects how evenly your home heats and how often the system cycles on and off. Here is a brief description of each type:

Comparison of Gas Furnace vs. Heat Pump

If you are weighing your heating options, here is how a gas furnace stacks up against an electric heat pump across the factors that matter most.

Does a Gas Furnace Fit Your Home?

A gas furnace is a dependable standard for residential heating, but it is not the right fit for every home. Because it relies on fuel combustion, it needs specific infrastructure to run safely, and it suits homeowners with certain comfort priorities:

In addition to these considerations, you may be wondering what size furnace do you need? Furnace heating output is measured in BTUs (British Thermal Units), and bigger is not necessarily better. A furnace that is oversized short-cycles, switching on and off rapidly. That wears parts out faster and leaves uneven warm and cold spots from room to room. A furnace that is undersized runs almost constantly and still struggles to keep up on the coldest days.

Learn More About The Furnace Installation Process

How to Ensure My Furnace Is Properly Sized?

Although your home's square footage can give you a ballpark idea of the furnace size you'll need, a properly-sized furnace depends on many more factors than just the square footage of your home. A proper Manual J load calculation accounts for your insulation levels, the number and type of windows, ceiling height, local climate, and how your ductwork is laid out. This is why an in-home assessment from a qualified technician is the most reliable way to match a furnace to your home.

Frequently Asked Questions About Gas Furnaces