It’s an industry standard: if a furnace has a cracked heat exchanger, it gets replaced. The American Gas Association has even put this in writing – they say “Any visible crack or hole is the reason for requiring replacement of the heat exchanger or furnace.” When we inspect a furnace and I find a cracked heat exchanger -it always is best to replace the equipment unless under the manufacturer’s warranty.

So what’s the big deal with cracks or holes? A cracked heat exchanger could allow exhaust gas from the furnace to contaminate the household air with carbon monoxide. The furnace produces levels of carbon monoxide AND the exhaust gas mixes with the household air. For a good example of a hazardous heat exchanger, check out the photo below showing a large rust hole in the heat exchanger of this high-efficiency furnace that was only ten years old.

What about a Carbon Monoxide Test?

A test for carbon monoxide (CO) can be inconclusive. A test for CO reveals whether a furnace is producing CO. A furnace creating CO is a symptom of bad combustion in a furnace because, unlike a car, CO is not a regular by-product of the furnace combustion process. Therefore, a heat exchanger can be breached and if the furnace is not producing carbon monoxide the breach will remain undetected.

1. What are the options if a Heat Exchanger is bad?

There are only two options if a Heat Exchanger is bad:

a. Replace the heat exchanger or replace the furnace. If the heat exchanger is under warranty, this option is a good way to go unless it is unavailable in the time frame needed, which can be immediate in cold weather.

b. The other factors are energy efficiency and cost of service which can make replacing the furnace a preferable option even if the furnace is under warranty and available. If a furnace is out of warranty the preferable option is to replace the furnace.
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2. What about a Carbon Monoxide Alarm?

Relying on a CO Alarm is not an acceptable solution for a bad heat exchanger. This would be as unsafe as driving a car that has a leak in the brake line – you might be able to brake a few times but you wouldn’t want to bet your life on it. Furthermore, it is against the Mechanical Code, Fire Department regulations, and policy to allow a furnace to operate that has a bad heat exchanger to. A representative from any of these organizations would shut the furnace down.