How Often Should I Change the Filter in My Minnesota Home?

The answer? Whenever it gets dirty.

OK, we know what you’re thinking: “Yeah, but how often should I be checking for a dirty filter?”  

Typically, you should check it once a month. But the real answer is it depends.

You see, how quickly your air filter gets dirty depends on the:

  • Weather
  • Filter’s MERV rating
  • Your home’s overall indoor air quality
  • Your thermostat settings

To give you a better idea of how often you’ll need to replace your air filter, we’ll explore each of the factors above and how they affect your filter performance.

Factor #1: The weather

How it affects your filter: The hotter the weather, the more often you’ll need to change your air filter.

You see, the longer the AC runs, the more air it pulls in through your air filter. And more air passing through your filter means more trapped air contaminants, causing the filter to clog up faster.

For example, let’s say it’s July and you’re running your AC all day to keep your home comfortable. You’ll need to check and change your filter more regularly than, say, in September when you won’t be running the AC half as much.

Factor #2: The MERV rating of your filter

How it affects your filter: The higher the MERV of your filter, the more often you’ll have to replace your filter.

The MERV of your filter determines how many particles it can trap. The higher the MERV of your filter the more particles it can trap, which means the cleaner your air will be but the faster your filter will clog up.

For example, the basic air filter used by most homeowners is the fiberglass air filter. These disposable fiberglass air filters are usually rated anywhere from 1 to 4 on the MERV scale and only catch larger contaminants such as dust mites, pollen and carpet fibers. Typically, these low MERV filters should be checked once every 3 months (depending on a few other factors) and changed once they look like the filter to the right below.

Note: If you’re not sure what MERV rating your current filter has, just check the side of the filter for a MERV rating label.

Fiberglass filters are usually anywhere from 1 to 4 MERV and typically need to be changed every 3 months.

On the other hand, a filter with a higher MERV of 13 may need to be replaced once a month. That’s because a filter with a MERV of 13 can catch a lot of contaminants (all the contaminants listed above for a MERV 1-4 filter plus finer contaminants such as tobacco smoke, bacteria, mold spores, etc.)

Note: The thickness of your filter also correlates to how long it will last before clogging up. A thicker filter has more surface area to catch more contaminants. So a filter with a MERV 13 that’s 1 inch thick will clog up faster than a filter with a MERV of 13 that’s 3 inches thick.

Factor #3: The overall indoor air quality

How it affects your filter: The more air pollutants you have in your home, the faster your filter will clog up.

The quality of your home’s indoor air determines the amount of contaminants floating around in your home. And the more contaminants there are, the faster your filter gets dirty and needs to be replaced.

According the the Environmental Protection Agency, some factors that can increase the amount of air contaminants in your home include:

  • Recent construction/renovations to the home
  • Use of pesticides in or around the home
  • Poor ventilation in the home
  • Smoking inside the house
  • Presence of indoor pets
  • Humidity levels that are too high or too low
  • Level of air pollution and construction around the home
  • Number of people occupying the home (the more people, the more contaminants)

For advice on how to cut down on indoor air contaminants, check out the EPA’s article, “Improving Indoor Air Quality”.

Factor #4: Your thermostat settings

How it affects your filter: Setting your thermostat fan to ON instead of AUTO will cause your filter to clog up faster.

Your thermostat provides two settings for your AC fan:

  1. ON
  2. AUTO

Setting the fan to ON means that the fan runs continuously, even when the AC isn’t on a cooling cycle. Setting the fan to AUTO means the fan runs only when the AC is on a cooling cycle.

So if you set to fan to ON and it runs continuously throughout the day, your filter is constantly trapping contaminants as air passes through the AC system. And that means it will get dirty and need to be replaced faster than a filter that only traps contaminants during cooling cycles.

Setting your fan to ON can also increase energy bills and humidity levels in your home. To learn more, check out our blog, “Should You Set Your Thermostat Fan Setting to ON or AUTO?”

Need advice from a MN tech?

If you need help controlling indoor air pollutants or aren’t sure what type of filter you should be using, we can help.

Just contact us. We’ll send over a professional who can give you helpful advice when it comes to your AC’s air filters.

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