How often should I change my air filter? This is something that we get asked very often, but to be quite honest there is no generic one fits all answer for this. If you change your filter too often then you are wasting money, and if you don’t change them often enough you can cause damage to your system. There are many factors to consider that can change our answer, and for some of you, save you money. Let’s dig into this topic a bit further!

MERV rating or (Minimum Efficiency Reporting Value): On the side of your air filter (if you have a pleated disposable filter), is a listed MERV rating, with the most typical ratings being 8,11, and 13 in a residential application. The lower the MERV rating, the less efficient that filter is at catching the fine particulates that you are trying to filter, and therefore a lower MERV rated filter will see a longer lifespan as it is catching less material. It is ok to put a higher MERV rated filter in your system, as long as you consult with your HVAC technician about static pressure on your system, and you are religious about checking them. The last thing we want is for a high MERV filter to go unchanged and cause your system to overheat.

Filter size: The size of the air filter, (Both square inches, and depth) make a huge difference when it comes to filtering your air properly. The best way we can describe this is in terms of air velocity. If you have a filter in stream of a duct system, and your furnace fan is moving at a constant speed, the size of that filter will make a direct impact on the efficiency of that filter. We always try to get the largest filter possible in your system because this means that the air will have a chance to move at a slower rate across that filter, which will significantly increase the effectiveness of that filter (because dust particulates are not shooting through the filter at a high rate of speed).

Filter type: Another significant factor to consider when determining the amount of time needed between filter changes, is the exact type of filter you have. Different filters include the following…

  • Pleated disposable: These are the most traditional type of filter that we see, and these are the most common type of filter that we install. these filters are a low-cost solution to get excellent filtration without breaking the bank, and because they are disposable, there is minimal effort required when it comes to replacing the filter, just throw it away, and put in a new one
  • Washable: If you have a washable filter, meaning it is meant to be reused and washed instead of being replaced, then there is no need to worry about buying new filters, but we must caution you that the efficiency of these type of filters is less than ideal. In most cases, these filters traditionally cannot catch particulates as a disposable pleated filter does
  • Electronic Air Cleaner: An electronic air cleaner is a washable/cleanable filter that is regarded as having the maximum efficiency, and electronic air cleaners that we install like American standard’s AccuClean is capable of removing 99.98% of airborne particulates down to .3 microns in size. Though these type of air filters are the ultimate solution for removing allergens, dust, and other particulates in your home, they do require cleaning more often than a traditional washable filter, simply because they catch more material, faster.

Home environment: The greatest factor to consider when determining your filter change intervals, is likely your home environment. How airtight is your home? Is your ductwork clean? Is your ductwork sealed? Do you have pets? Do you have a dusty environment outside the envelope of your home? Do you smoke in your home? Do you have carpets? These are just a few environmental factors that can contribute to an increased filter change interval

Return air location: You may or may not have noticed a return air grille in your home. this is typically a large grate located in the ceiling, floor, or sidewall of a central location in the home. this return air drawing air from your house, through the filter, and then back into your house via the heat registers in your home. the location of this grill is important only because if you have pets, or an excessively dusty home, odds are that most of the material lying on your floor will not be able to travel to the ceiling height and therefore may never each your filter, to the contrary, if your return air grille is located in the floor, or sidewall, you likely have a much better chance of those materials passing through your filter, and you may need to check your filter more often

Equipment runtime: Here in the pacific northwest, we service and install a wide variety of equipment, and now more than ever we install Air Conditioning onto existing heating systems. If this is the case, the fan on your heating equipment is being used to force cool air throughout your home, and therefore your filter is being used almost year round. You will likely need to replace or clean your filters twice as often as somebody who is only running their fan in heating mode. If you only have a heating system, and you simply run your fan in spring and summer time to circulate air, then you will also need to replace your filters more often.

The burning question….When do I change my filter?: The only real way to answer this is to take all of the factors provided above into consideration and do a test trial on your home. The average lifespan we see of a filter, either Washable, Electronic, or Pleated, is between 3-6 months. Though it can’t hurt your system to change every 3 months, we often find with filters such as a 4″ thick, Merv 8, (which costs more than a traditional 1″ pleated filter), that 4-6 months is an ok change rate, which over the lifespan of your home can equal hundreds and hundreds of dollars. In the pictures below you see three levels of filter use. The one on the left is new, the middle one was in use for 3 months, and the one on the right was in use for a year. As you can see there is a dramatic change in color from the new one, to the oldest one. though the one in the middle was used for 3 months, it is actually still ok! when we held it up to the light as seen in picture 2, there is still plenty of space for air to travel through, as opposed to the 1-year-old filter that we can hardly see light through, and will likely cause a service call.

What filters we put in on new installations: As a company policy, we do everything we can to get a properly sized 4″ MERV 8 media filter as close to your furnace as possible. Aside from a 4″ media cabinet, we also install a large amount of AccuClean electronic air cleaners for those with allergies and dust issues. We try everything possible not to put in filters in the return grille of a home, but when we do we always verify a complete seal from the return duct to the furnace or Air handler so that we know we are not drawing unfiltered air from outside the envelope of the heated space.

If you have any questions on this topic, feel free to give us a call. We are happy to help!

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