How Do You Know If Your Furnace Has An Exhaust Issue?

In the past, gas and oil furnaces relied primarily on gravity to move combustion byproducts away from your home. These gases are extremely harmful, so it's important to keep them safely away from living spaces. With old, standard-efficiency furnaces, so much heat energy remained in the exhaust stream that the gases could naturally rise through a flue pipe and exit the home. 

However, modern furnaces extract more heat from the combustion process. As a result, gravity is no longer sufficient to pull combustion gases away from your home and furnace. Instead, newer furnaces rely on a draft inducer motor to pull combustion gases through the exhaust system. This more complex arrangement is more efficient but prone to several problems.

What Does Your Furnace's Exhaust System Do?

The draft inducer in your furnace serves a few different purposes. First and most importantly, it ensures that combustion gases continuously flow through the exhaust flue and outside your home. The draft inducer creates negative pressure that constantly pulls combustion gases through the furnace's heat exchanger and into the flue.

While this process helps your furnace run safely, it also improves efficiency. Combustion gases that remain in the combustion chamber can affect the air-to-fuel ratio of your furnace, resulting in incomplete or inefficient combustion. Excess waste gases in the combustion chamber can lead to flame rollout, delayed ignition, and other serious problems.

What Can Go Wrong With Your Exhaust System?

In most cases, the exhaust system in a gas furnace will only consist of a few components. In addition to the exhaust flue, there's the draft inducer motor that produces negative pressure and a pressure sensor that proves the proper operation of the draft inducer. Issues can develop in any of these three components, potentially causing your furnace to run inefficiently or stop working altogether.

Common failures include bad pressure switches, faulty draft inducer motors, and clogged exhaust flues. In all three cases, the pressure switch will typically report a fault to the furnace control board, preventing the ignition sequence from completing. As a result, your furnace may begin to go through its startup sequence but fail to ignite its burners.

Note that exhaust systems problems can also sometimes cause inefficient or unusual operation. A partially clogged exhaust flue may not trigger the pressure switch but can create pops or bangs due to delayed ignition. The furnace may also run intermittently if the draft inducer motor is in the early stages of failure.

What Should You Do About Exhaust System Issues?

Remember that your furnace's exhaust system is a critical safety feature. In many cases, exhaust flue design must follow strict building code regulations. If you suspect a problem with your furnace's exhaust system, always rely on an HVAC professional for a full diagnosis and repair. Attempting to fix the problem yourself may result in an incomplete or even unsafe solution.

Contact a local furnace repair service to learn more.