Too much airflow causes the heat exchanger to run cool causing condensation to form inside, and if you read the previous articles you know what that means.
(If you don’t, then read Heat Exchanger Failure #2 and #3…)
If you don’t have enough air flow the heat exchanger will run too hot, causing it to crack.
How hot should it be? Well, if the firing rate is correct, and the air temperature rise is within the manufacturer’s specifications, you should be good.
That’s it for this series of articles. There are other things that can cause a heat exchanger to fail, these were only the top four offenders, or what would be considered the most common.
Others causes of heat exchanger failures include flue gas from another unit being drawn in with the combustion air, corrosion from salt water (coastal dwellers only) and uneven air flow over the heat exchanger tubes.
So, with the right firing rate, air flow, and a clean combustion air supply, your heat exchanger should last for years.