A Dirty Furnace Filter could cost you $1,000.

How often do I really need to change my furnace filter? Skipping that $10 filter change could cost you $1,000.

How often should I change the filter in my furnace? As a 10-year veteran of the residential HVAC service industry, this is the question I get asked most frequently.

The answer is simple, it is the same for everyone yet also different. Your filter needs to be changed at the end of its' service life. The difficult part, especially for those not trained in HVAC, is that there are a multitude of filter styles. Each style has its own unique service life. Let me cover 3 of the most common types, then I'll share a story that will motivate you to change your filter often. Odds are, the furnace in your home uses one of these.


1" non-pleated filter - 30 days

Thankfully, I don't see nearly as many of this style filter as I once did. The non-pleated design fills up quickly with dust and pet hair. It does a fantastic job of restricting airflow and damaging your equipment when left unattended. If you have one of these inside your furnace, make sure to replace it every 30 days. Better yet, upgrade to a pleated style of the same dimensions and your furnace will be breathing much easier.

1" pleated filter - 90 days

These guys have been the king of filter-mountain for the last decade. If your HVAC equipment was installed in the last 10-20 years, you probably have a pair of these inside your furnace or duct work. The good news is that the pleated design creates peaks and valleys which can trap up to 3 times as much airborne particulate as a non-pleated version. This increased surface area allows up to a 90 day service life. The bad news is that going 3 months between changes makes it an easy chore to forget..Before you know it, you could be going for a year on the same old plugged up filters. Set a reminder in your calendar to install a new set with every season change.

4" pleated filter - up to 1 year

These guys have quietly become the new standard in home hvac filtration. Due to the increased airflow requirements of today's variable-speed blower motors, many furnace manufacturers list this filter as a minimum requirement. This is great news for homeowners and service technicians alike. These 4" deep pleats allow for a serious increase in airflow. Additionally, the construction of these filters can trap much smaller airborne particulate that would otherwise pass by the 1" pleated and non-pleated filters. Less stress on your equipment, cleaner air, and up to a 1 year service life. Now that's a filter I can get behind!

As Industry professionals, we always say “up to” in regards to filter service life. This is because a home with multiple dogs and cats will require a fresh filter sooner than a home without pets. I have seen 4" pleated filters require replacement after only 6 months. I have seen others look almost brand new after a whole year. It really does fall on the person who services the filter to determine how frequently a change-out should occur.


But the title of this article says that if I skip a filter change, It could cost me $1,000.. how is that possible? Well, let me tell you a story (with visual aids!) about how skipping a few filter changes cost one of my clients $1,000.

The pleasant Mrs. Janice...

I went on a typical "no-heat" service call last week. A new client, lets' call her Janice. She called in to report that she was seeing smoke coming from her furnace vents, and would like a technician to come out and take a look. Naturally, we set up a service call immediately. Upon arrival, Janice was pleasant and eager to show me exactly what was happening. Sure enough, she turned on the thermostat and after about 30 seconds of small talk, I observed smoke billowing out of the return air vent in her hallway. After quickly shutting off the thermostat I asked Janice to lead the way to her furnace.

Upon arrival, I removed the furnace doors and this is what I saw: Two dirty filters. They were plugged up and causing such a restriction that the blower motor actually sucked one down off its perch. As soon as I removed the doors, I could smell the unmistakable odor of a cooked blower. I removed her pleated filters which have a service life of 90 days. It was overwhelmingly clear that Janice had not changed her filters in quite some time.

Mrs. Janice proceeded to explain that she had moved into the home 2 years ago and was never instructed as to the location of the filters or how frequently they should be replaced. My 10 years of experience as a residential HVAC service technician told me that the blower motor had burned out due to restricted air flow caused by the extremely clogged filters. However, I still needed to verify this by performing a diagnostic and carefully testing the other components to make sure no additional damage had been done.

After completing a thorough diagnostic, I was able to determine that the blower motor was not the only failure. There were actually 3 other components that would need to be replaced in order to return the furnace to proper and dependable operation. The total bill for this repair came up just shy of $1,000. This was not the news Janice was hoping for, however it was 3 pm on a Thursday afternoon and snow had been falling for a few hours already. Not wanting to go the night without heat or wait a few days for us to install a whole new furnace, Janice made the difficult decision to proceed with the required repairs.

Now the moral of this story is this: The best way to prevent unexpected and expensive repairs to your HVAC system is quite simple. Change your filters at the end of their service life. If you don't know when this is, contact a professional. Also, you should have your equipment maintained annually to ensure everything is operating properly. In this story, a $10 pair of filters from the local hardware store could have prevented $1,000 of unexpected repairs and a lot of stress. Lets not even think about what could have happened if Janice was not home to see the smoke billowing into her hallway and able to quickly shut off her furnace….

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