Types of Furnaces

Learn more about quality and performance factors..

Heat Exchanger

The main difference between gas furnaces is the number of heat exchanges in the furnace.

HEAT-EXCHANGERA heat exchange is a series of tubes or pipes that  are used to transfer heat from the furnace into the home. The hot gases produced by the burners enter and travel through the heat exchanger. The combustion gases, which are now cooled down, are then directed into the venting pipes by a draft inducer blower and taken out of the home.

As the hot gases pass through the heat exchanger, heat is transferred to the exterior walls. The furnace blower moves air over the exterior walls of the heat exchanger absorbing the heat.  The heated air then moves into the duct work where it is distributed throughout the home.

One of the most common problems with a heat exchanger is when it begins to crack from normal wear and tear.  When this occurs, it allows the carbon monoxide that is created by the combustion to leak out and into the home.  Carbon monoxide (CO) is a colorless, odorless, and tasteless gas that is slightly less dense than air. It is toxic to humans, causing illness and even death.

Conventional Furnaces

Conventional Gas FurnaceA conventional furnace has a single air exchanger that captures up to 80% of the heat that is generated through combustion. That means around 20% or more of the heat from combustion is exhausted into the outside air before it can be used to heat the home. That means about 20% of what you pay for fuel goes out the chimney!

Although the gases are cooled as they go through the heat exchange,  they are still very hot when they exit. Therefore a Type B , double walled vent pipe is required. These are made with a galvanized exterior, and an aluminum interior that create a small air insulating space between the walls. But even these pipes become hot enough to cause a burn if touched.

Condensing Furnace

Condensing Gas FurnaceThe condensing furnace does not have a significantly more efficient combustion process than a conventional furnace. The difference lies in that the condensing furnace has a more efficient heat extraction process after combustion.

A conventional furnace will exhaust its combustion gases quickly, causing the gases to exit the chimney flue before cooling and condensing. As a result, the conventional furnace heat exchanger does not extract as much heat from the fuel combustion process as possible.

A condensing furnace extracts heat for a longer period of time, to the point where exhaust gases having “cooled” and condensed. This is accomplished by using two heat exchangers, one for primary heat exchange and a secondary heat exchanger to handle the corrosive condensed exhaust gases of water and carbon dioxide (which form carbonic acid).

The exhaust gases are depleted of heat until the water condensate drips out of the furnace’s heat exchanger and the flue gases escape from a plastic PVC pipe instead of a chimney.

Condensing furnaces are extremely efficient, pulling up to 98% of the heat out of the gas before it exits the chimney.