how often should I change my a/c filter

How Often Should I Change My A/C Filter?

  • July 30, 2015
  • By MR COOL

You change the oil in your car. You wash it. You keep up the maintenance. You do those things, because they’ll keep the car running longer. You should be doing the same sort of things for your air conditioner. So, have you ever asked yourself, “How often should I change my A/C filter?”

If you did, and couldn’t find an answer, we’re here to help.

So…How Often Should I Change My A/C Filter?

The quickest answer is, “It depends.” Which is, as answers go, pretty unsatisfying.

Before we go more in depth on that, let’s discuss what exactly the air filter does for your air conditioner.

Your air conditioner sucks air out of your house, drags the heat out of it, blow that now much cooler air back into your house, and spits the heat outside. It’s a basic cycle we’ve perfected over the last hundred years or so. The problem with that cycle is air impurity. You can’t often see it with the naked eye, but air is rarely empty. There’s bacteria, dust, pollen, mold spores, plant debris, and all sort of other gunk rolling around in the atmosphere. When your air conditioner pulls the air into the system that junk comes along.

These pollutants then do one of two things. They either get caught on the coils or spewed back into the house with the now cooled air. Neither is good.

Dirty Coils = Operating Inefficiency

The heat transfer coils inside your air conditioner are critical. They need to be able to transfer heat efficiently and cleanly. Any dirt, dust, or debris that builds up on those coils will affect how effectively your air conditioner runs. The more dirt, the lower the efficiency. If you run dirty cools for long enough, then you are headed for a mechanical breakdown, my friend.

And those are never cheap.

The a/c filter’s main job is to protect your coils. Fewer foreign particles making it through the filter means less build up on your coil, and that is a very good thing. Of course, you still don’t know how often you should change your a/c filter, so let’s hit that next.

2 Weeks Minimum, 3 Months Maximum

Some people should change their coils every 2 weeks to a month. Others can get by with doing it every 2 or 3 months. How do you know where you fit?

It’s not that hard to figure out. If you have a lot of people or pets living in your house, you’re going to need to change the filter more regularly. If you’re a single person who works long hours and travels a lot for business, you can get  by changing the filter more frequently.

There is a good rule of thumb you can use to judge though. Take out a filter you’ve been using for a while. Can you see through the mesh? No? Change it. If it’s not that dirty, it can go a little longer.

But, hey, don’t just take our word for it. Insurance company Allstate would also like for you to change your a/c filter on a more regular basis.

Of course, you can trust them.

They’re an insurance company.

27 thoughts on “How Often Should I Change My A/C Filter?”

    1. The DIY air handler filters are meant to be washable and re-usable. If you have lost or damaged yours, please contact us at 270-366-0457.

  1. I am in the market to buy the 36k btu single unit DIY, I have already installed the 16k unit for my dad and he loves it and I’m highly impressed. I am curious to know if Mr Cool offers a better filter such as a HEPA type filter or something that catches more dirt and debris than the “screen” type reusable filter? I’ve had window units in my home that have screens and they aren’t very effective at stopping the dirt and dust from getting thru them and clinging to the evaporator. I clean the coils annually but still would like to stop more dirt from getting through. If Mr Cool doesn’t offer a solution, can you recommend something else that will work? Thank you!

    1. We do not currently offer any other kinds of filters for the DIY. The best solution currently would be to clean the existing filter more regularly.

  2. My manual says to replace the air freshening filters (the little green fiters attached to the larger filter) every few months. I have a DYI 3600. Were can I buy these filters?

  3. Hi where can I get the mini filter that goes in the middle of the larger filter ? What is the purpose of the small filter ?

  4. Hi:
    I need replacement nylon filters please. What size do I need for the DIY 18 and where can I buy them. My unit is up really high and would be much easier if I can just switch out the dirty with the clean.

    1. The filters were made to be washed, but if you give us a call at 270-366-0457 we’ll see if we can figure something out specific to your needs.

  5. Hello, I have the 4-5 ton universal MDUI18060 model. What is the recommended filter thickness and Merv rating for this? I would like to use a 4″ thick 20″x 25″ Merv 11 filter, will this cause any issues? Thank you

  6. The little green filters that attach to larger filter mrcool calls them air freshener, give a Hvac supply house that carries them in my area 18704 Wilkes barre pa. They don’t know what i am talking about. Doesn’t mrcool carry these filters? It’s a pain

  7. I just installed a 2T/3T Universal system. II works great! What is the maximum MERV rating you would recommend if using 1″ filters?

    1. With adequate ductwork (low static pressure), you could use MERV11. In most cases, I try to stay at MERV8 or below to keep from restricting air flow too much.

    2. I installed the same system in my house with new duct work. I erred on the side of slightly oversizing my duct work for quiet operation and lower SP. During the winter time (heating mode) and wanting to reduce potential viruses/bacteria, I’ve been running MERV 13. It does restrict airflow a little more so I’ve been changing mine every 3-4 weeks. I think the key is paying attention to your system. I think when you get on the finer side of filtration you just need to make sure you keep up on filter changes. When I get back into summer months (cooling mode) I will drop back down to an MERV 6 or 8 for airflow as I want plenty of air passing through cold coils.

  8. I’ve had a Mr. Cool minisplit for a year now, but just activated the wifi connection and am using the app to manage it. One thing I need to change is the interval at which I am reminded to clean the washable filter. It is not even close to dusty at 2 weeks and the interval needs to be longer. How can I do this?

    1. We would recommend you clean it every 2 weeks. Ideally, you should not wait until it is covered in dust to clean.

  9. Is there a MERV rating given to these mini split filters. As wildfire smoke engulfs the midwest, it would be good to know which particulates are sneaking through and if there’s a way to upgrade to a stronger filter.

    1. With wildfire smoke in particular, it would be best to invest in an air purifier. The mini-split’s filter would be able to catch some of the particulates, but not to the level of a dedicated air purifier.

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