How Often Should I Replace My Air Filter?

One of the most common questions for those running a HVAC system in their home or business is how often the air filter should be changed.

There’s no single answer to this question, as it can depend on

  • The environment
  • The number of people living or working in space
  • The presence of pets or smokers
  • The brand of the system

The amount each property runs their HVAC unit varies considerably which impacts how clogged the filter will get over time. But here are some tips to consider when you’re considering replacing your air filter, from what to look for to factors that can make a filter get dirty more quickly.

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Things to Watch Out For

An air filter should typically be changed every three months if the filter is between 1 to 2 inches. For common furnace filter sizes, such as four-inch filters, you can replace them on average every six months while five-inch filters can stay in place for 12 months before needing to be replaced. There are signs you can look out for though to know whether your air filter needs to be changed before these time frames. These include:

  • The filter is visibly dirty and is covered in dirt, dust and debris. If you can’t see the material of the filter, it should be replaced.
  • The unit itself is running more frequently than it normally does.
  • Your home is dustier than normal.
  • You have noticed a strange burning smell coming from the HVAC unit.

Impacting Factors

Changing the filter regularly will keep your home clean and free from allergens and contaminates. But there are certain factors that can speed up the timeframe in which your air filter needs to be replaced.

For example, if you have animals in the home, this will shorten the length of time between needing to replace the filter, as pet dander and dirt brought in from outside can speed up how quickly the filter becomes clogged. The more animals you have, the thicker the filter should be. Similarly, if there are smokers living in the property, this will have an impact on the lifespan of the filter.

If you have the windows and doors open often in your home, this can allow pollen and other allergens to enter the home, so you should consider this when choosing the air filter for your HVAC system. Excessive dust is another factor that can make your furnace filter last less time.

If there is a lot of dust in your home, you will need to change one and two-inch filters every month, four-inch filters every two months and five-inch filters on a three-monthly basis. Finally, allergy sufferers will find that their allergies flare up more as the air quality dips. So, if anyone in the home has allergies, consider changing the filter on a more regular basis to keep the air quality as high as possible.


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