• James Knott

Why do heat exchangers fail?

In my last blog I talked about filters and how often to replace them. I did that so I can talk about heat exchanger failure. Heat exchangers fail for only one reason, THEY OVER HEAT! The real question, how many different ways to they over heat?

1. Filtration

2. Oversized furnace

3. Undersized delivery system

4. Too much gas pressure


Lets start with filtration.First off, a proper filter system should be sized according to the manufacturers guidelines. Your filtration system is an integral part of your comfort system it is designed to allow a certain amount of air through as it cleans dust out of the air. As your filter gets dirty it can make the furnace get hotter than it is designed to get. All furnaces work on a temperature differential usually between 35 and 70 degrees Fahrenheit. If for any reason the furnace haw over a 70 degree temperature rise the heat exchanger is getting hotter than its suppose to therefore fails prematurely.

Oversized Furnace

Your furnace is designed in Monroe, Michigan to heat your home to 70 degrees on a 0 degree day outside. At these design temperatures It is not uncommon for a furnace to run not stop to properly heat your home. If the furnace is too big for your home the heat that is produced in the furnace can not leave the furnace. If the heat stays in the furnace it will naturally overheat therefore exceed manufacturers specifications and cause premature failure of parts and the heat exchanger.

Undersized Delivery System

The delivery system (ductwork) in your home should be sized to get rid of the heat in the furnace. The proper way to have your ductwork checked for sizing is by having the pressure checked. The T.E.S.P. or total external static pressure should never exceed .5 in Water column or check rating plate for manufactured specifications. If the duct system I too small for the furnace the air will move too fast over the heat exchanger and not pick up the heat. If the heat stays in the heat exchanger the heat exchanger will exceed its design temperatures and fail prematurely.

Too Much Gas Pressure

All equipment comes with a gas regulator in them called a gas valve. This valves sole purpose is to open when told and feed gas to the combustion chamber to heat up the heat exchanger. It is designed to not be higher than 3.5 inches water column for natural gas or 10 inches water column for propane. if these pressures are too high we are feeding too much gas into the heat exchanger which produces more heat than needed. when this occurs as previously said the heat exchanger gets hotter than its suppose to creating premature heat exchanger failure.

All of these issues that cause overheating of the heat exchanger can/should be checked on an annual basis during an HVAC tune up or maintenance visit. The 2 most commons reasons for overheating the furnace is filtration and gas pressures, which can be adjusted and changed annually. To have your system checked for over heating issues contact Complete Home Comfort at (734)384-3910 or find us online at www.completehomecomfortmonroemi.com.

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Tel: 734-384-3910