What’s the best way to inspect a heat exchanger? Most state and association “Standards of Practice” don’t require a home inspector to inspect the heat exchanger.  However, a good inspection practice is; if you come across a conventional furnace where heat exchanger openings are larger and give the inspector access with his or her mirror, then the inspector should take a look.

Do you have access?

New high efficiency furnaces have sealed combustion so you cannot see their exchangers; mid-efficiency units typically have smaller openings that make it difficult to get a mirror in.  Oil fired units are also typically not visible.  It’s a good idea to inform your customer that about only 25% of the heat exchangers in a conventional gas furnace are visible with the mid, high and oil being much lower or not visible at all.

Accessible exchangers

If you do have access, use your flashlight and inspection mirror to look for cracks.  Be especially careful when looking at curves and welded areas.  Some things to look for that can indicate a cracked or faulty heat exchanger are scorch or burn marks on the furnace jacket, staining around registers or on front of the furnace, corrosion, rust or soot build up on or below the heat exchanger, and unusual flame activity.

With a boiler, the heat exchanger will not be visible for inspection.  As you examine the burner area note if there is any evidence of leaking from the heat exchanger onto this area. In many cases there would be signs of rusting, corrosion, flaking metal, or water seepage and even dripping water.

In any of the circumstances mentioned above, suggest a qualified service technician examine either the furnace or boiler if you identify a potential problem. Your customers will greatly appreciate it.