Natural Resources Canada recommends changing the furnace filter at least once every three months and cleaning the oven and ducts annually. However, research shows that Canadians don't change their furnace filters as often as they should. The EPA (Environmental Protection Agency) regularly publishes filter guidelines and communicates them to the public, but there seems to be a disconnect. The filter in your furnace has a dirty job: it collects dust, hair and other small particles suspended in the air so that they do not damage the components of the oven.
Depending on the environment in which your furnace operates, most HVAC companies recommend changing all filters at least twice a year. If your home is located in an area with a lot of dust or dirt, you may want to change them more often to prevent clogging and decreasing the efficiency of your heating or air conditioning unit. However, there are other factors that will help you determine how often air filters should be changed. How often you need to change your furnace filter really comes down to what is happening in your home. Thomas & Galbraith Heating, Cooling and Plumbing of Ohio recommends changing filters less than 2 inches thick every 30 to 90 days.
Your furnace's owner's manual will specify the best MERV rating for your furnace, and in general, filters with a MERV rating of 6 to 9 should be changed every 90 days, while those with a MERV rating of 10 through 12 should be changed every 60 days. The real problem is not always when to change the heating and air conditioning filters in your home, but rather remembering when to change them. Clogged filters not only adversely affect the air quality in a house, but also force the furnace to work harder to draw air into the system and thus be able to shorten the life of the furnace. Once you have changed the filter, turn on the furnace again. Check the filter monthly and clean the washable filter or replace the disposable filter every 90 days.
Install a new filter before restarting the unit, but if you don't have filters on hand yet, just run the air conditioner without it. Use a filter with a MERV rating of 12, such as the Nordic Pure Filter (available on Amazon), if your furnace can handle it. It's best to confirm what your MERV rating converts to make sure you're using a safe filter for your furnace. Even if no one in the household is allergic, it is advisable to change the furnace filter frequently, every 30 days if you have several pets, so that the furnace works efficiently. This may be a good guideline, but if you suffer from severe allergies, you might consider changing them more often. Filters receive a Minimum Efficiency Report Value (MERV), which ranges from 1 to 16, although ratings of 6 to 12 are best for residential furnaces.
So, even though your filter may seem clean at first glance, the reality is that there is no way to tell just by looking at it.
