What Is a Condensing Furnace?

Condensing furnaces, two-stage furnaces, heat pumps — oh my! With so many heating system options, it's not easy to choose one for your home.

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A condensing furnace is one option if you're looking for high-efficiency heating.

What Is a Condensing Furnace?

Gas furnaces use a combustion process that results in some lost heat, which occurs as water vapor that's lost up the chimney. A condensing furnace is a high-efficiency model that includes a second heat exchanger to capture that heat and use it to heat your home. It also typically has extra features, such as variable-speed blowers, that increase the energy efficiency even more.

How Does a Condensing Furnace Differ From a Traditional Furnace?

A traditional furnace has just one heat exchanger, while a condensing system has two. The main difference is what happens to the exhaust gases. In traditional systems, they're lost through a metal flue and vented outdoors. A condensing furnace captures the heat, sends the water through a drain pipe and directs the remaining gases outdoors through a plastic pipe instead of a metal flue.

How Does a Condensing Furnace Work?

Heating your home starts similarly in both a condensing furnace and a traditional furnace. The air goes through the primary heat exchanger and moves through the vent system to heat your home. The gases from the combustion process then go into the secondary heat exchanger, which pulls out more heat from the exhaust. Because the remaining exhaust is much cooler, this type of furnace can use a PVC vent pipe instead of a metal flue. It can also go out through the wall instead of the roof like a traditional furnace.

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What Are the Efficiency Benefits of a Condensing Furnace?

Condensing units are high-efficiency furnace options with the highest annual fuel utilization efficiency (AFUE), which quantifies the appliance's efficiency at converting energy from fuel to heat during an average year. Think of it as how much of the fossil fuel gets turned into heat — an AFUE of 85% means 15% of the energy is lost as heat exits the flue.

A condensing furnace has an AFUE between 90% and 98.5%. Mid-efficiency furnaces typically range from 80% to 83%, while older furnaces can have an AFUE as low as 56% to 70%. That means condensing furnaces have the least amount of energy lost. That higher efficiency is better for the environment and saves money on your utility bills.

These models also have other energy-efficient features that help with operations. Some of those features include:

• Insulated blower compartments: This helps reduce heat loss and shorten the amount of time your system has to run to heat your home.

• Variable-speed blower motors: Condensing furnaces typically have blowers that can adjust to different speeds based on heating demands instead of only running at full blast.

• Sealed combustion chambers: The air supply for a condensing furnace comes from outside instead of inside the house like a traditional furnace. This sealed combustion chamber design reduces heat loss for greater efficiency.

• Two-stage gas valve: Another common feature is a two-stage gas valve for the burner. This allows for low and high settings on the valve based on your heating needs. When paired with a variable-speed blower motor, the system can reach more precise heating levels for effective temperature control and efficient operation.