8.7   Inspecting Furnace Heat Exchangers

Leaks in heat exchangers are a common problem, causing the flue gases to mix with house air. Ask customers about respira­tory problems, flue-like symptoms, and smells in the house when the heat is on. Also, check around supply registers for signs of soot, especially with oil heating. All furnace heat exchangers should be inspected as part of weatherization. Con­sider using one or more of these six options for evaluating heat exchangers.

1.      Look for rust at exhaust ports and vent connectors.

2.      Look for flame-impingement on the heat exchanger during firing and flame-damaged areas near the burner flame.

3.      Observe flame movement, change in chimney draft, or change in CO measurement when blower is activated and deactivated.

4.      Measure the flue-gas oxygen concentration before the blower starts and then again just after the blower starts. There should be no more than a 1% change in the oxy­gen concentration.

5.      Examine the heat exchanger by shining a bright light on one side and looking for light on the other side using a mirror to look into tight locations.

6.      Employ chemical detection techniques, according to the manufacturer’s instructions.