Understanding the Types of Gas Furnaces

This side-by-side comparison of gas furnace types makes it easier to understand your choices.

When replacing your gas furnace, you’ll face some crucial decisions that can affect your comfort and your wallet for years to come.

“A furnace is a big investment,” says Russ Katsov, an HVAC expert for Sears Home Services. “You can better make an informed choice by learning about the different types of gas furnaces available.”

Katsov also points out that furnaces made after July 2019 must have blower fans that meet new efficiency requirements. So if you've been putting off furnace replacement, now's a good time to make it happen.

Here are some helpful comparisons to help you decide what type of new furnace best fits your needs.

Single-Stage and Multi-Stage Furnaces

What They Are

A single-stage furnace supplies gas to the furnace burner at the same rate. The burner always heats air at the same intensity: hot.

A multi-stage furnace varies gas flow and burner intensity to more comfortably and efficiently heat your home. There are two types of multi-stage furnaces:

*The simplest multi-stage furnace is a 2-stage design that delivers low heat most of the time and high heat when needed during harsh winter days.

*A modulating multi-stage furnace varies burner intensity in 1-percent increments to smoothly deliver just the right amount of heat to rooms in your home.

Side-by-Side Comparison

Cost: A single-stage furnace is less expensive. It's also less expensive to repair.

Comfort: If you don't like feeling an intense blast of hot air every time your furnace turns on, you want a multi-stage furnace. Multi-stage furnaces also run quieter than single-stage units unless the burner is at full intensity.

Efficiency: The multi-stage is more efficient, which matters most in cold climates where the furnace runs for months.

Single-Speed and Variable-Speed Furnaces

What They Are

A single-speed furnace has a blower fan that always runs at a high speed.

A variable-speed furnace has a fan with more speeds. There are two types of variable-speed furnace fans:

• A multi-speed fan has 2 speeds: low and high. The fan typically runs on low speed about 75 percent of the time, kicking up to high speed when needed to bring the temperature up to the thermostat setting.

• A variable-speed fan has an infinite number of speeds within its range. Typically, an electronic control board regulates the speed. The fan usually starts at a slow speed and gradually speeds up for a smooth heating transition. A variable speed fan can run almost constantly, to circulate air through the home; that way air continuously passes through the air filter and doesn’t stagnate in the air ducts and become cold.

Side-by-Side Comparison

Cost: A furnace with a single-speed blower fan motor is less expensive. It’s also less expensive to repair.

Comfort: The variable-speed blower fan motor is quieter and delivers smoother heating through the room air vents in your home. Although it's more expensive, you'll see lower electric bills and feel more comfortable in your home with a variable-speed blower.

“Don't be overwhelmed by the choices that you need to make when buying a new furnace,” says Katsov. “Be confident in your knowledge about the different types of furnaces and pick the furnace that best fits your needs.”

To learn more about your furnace options, schedule a furnace repair appointment.