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The Fine Points of Furnace Filter Maintenance

If you're like the typical homeowner, you know that furnace filter maintenance is important, but you may not understand why. The air filter is the part that protects the HVAC equipment from excessive wear, and it goes a long way toward keeping your energy bills lower. 

The reason HVAC-industry engineers use filtration systems for forced-air equipment is that a lot of air passes through the indoor blower and even in the cleanest homes, dust is ever present. Dust infiltrates the parts inside your furnace and interferes with the operation of your whole system. If your home has a forced air cooling system, the dust can reduce its performance, as well. 

Changing Your Heater's Air Filter

It's a good idea to check the air filter monthly and change it when it's covered with dust. How often it needs changing depends on the number of people and pets in your home and the amount of dust in your outdoor environment, but doing as every three months is a good minimum. Larger homes or those with fur-bearing pets usually require more furnace filter maintenance because of more dust, hair and dander in the air. 

When you replace the filter, make sure you consider the following:


Most of the time the filter is easy to locate, especially if your furnace has an open return where the air's pulled directly into the system from the furnace itself. If you have return registers, the filter will be somewhere along the course of the return ductwork.

If you have trouble finding it, an HVAC technician can help locate it for you. If it contains no filter at all, it's possible a previous homeowner removed it and in that case, the HVAC technician should clean the blower thoroughly in addition to handling furnace filter maintenance. Running a furnace with no filter guarantees you'll have dust covering many of the inside furnace parts. As a consequence, your heating bills can be unnecessarily high.


Even the best air filter won't work as effectively if it's not the right fit. Measure the filter, including its thickness, before you head out to purchase a replacement. The replacement needs to be the precise size as the filter frame requires.


Check your furnace's owner's manual to learn the maximum density you can use in your system. The minimum efficiency reporting value (MERV) ratings for filters can guide you as to the size of the particle they trap.

The MERV scale runs from 1 to 16 for residential HVAC equipment, with higher ratings indicating more particle entrapment. In most cases, using a filter with a rating between 5 and 8 is sufficient for cleaning the air in homes. Going over 9 can impair the airflow through the blower, unless your heating system specifies that it can handle it. If you can't find the maximum value, contact an HVAC contractor who can look up the information for you.

The inexpensive fiberglass filters have a MERV rating from 1 to 4 and are not the best options for these systems because they allow larger particles that can damage your equipment to pass through.

The pleated filters you see in retail stores have ratings between 5 and 8 and offer solid protection against dust building inside the blower and keep your indoor air cleaner. The pleats offer more surface area on the filter and the paper from which they're made allows easy passage of air through the blower.

Making it a habit to perform furnace filter maintenance monthly will prolong the life of your equipment. Besides using a calendar to remind you to check, you can also install a device that measures the airflow through the blower that will alert you when the airflow starts to slow.

Heat Exchanger Issues

Slow airflow makes your heating equipment run longer to meet the thermostat's setting, therefore raising your energy bills. The heat exchanger in the furnace will stay hot longer, which can weaken the metal. Over time, the heat exchanger may crack, which is a dangerous condition since these cracks can emit carbon monoxide into your home's air through the ducts.

HVAC technicians and gas company representatives have to disable furnaces with a cracked heat exchanger and can't return it to service until it's been fixed or replaced. It can take weeks to get the part to repair it and repair and replacement is expensive. 

If you'd like more information about furnace filter maintenance and would like to learn more about increasing the efficiency of your heating system, contact We provide a full range of HVAC services for metro Chicago, southwestern Michigan and northwestern Indiana homeowners. 


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