To determine the size of air filter you need, simply remove the old filter and look at the sides of the filter. A label should be affixed that indicates the approximate size of the filter. If you are unable to find the size of your filter, you can call us with your model number and our filter expert would be happy to help you. When you replace your filter, it is a good idea to write the date of replacement on the side of the filter so that you can easily assess the time for a change.