You should always inspect monthly, and possibly change the filters on your furnace monthly. Many experts will advise you to change your furnace filters monthly, but that’s not always necessary. For smaller families without pets or allergies, you’ll likely be okay changing the filters every 2-3 months. If the filter is dirty, change it out, otherwise inspect it again next month. I have also been told by handymen to go with cheaper filters and replace them more often versus going with the expensive filters. Please always remember to use the correct size for your particular furnace. Using a different size or not one at all can cause harm to your furnace.
When you buy a home it really should come with instructions. If nobody tells you or leaves you the manual how are you to know how to take care of your Furnace? I would start by going on line to the Furnace manufactures website and I am sure they will have an online manual you could refer to. If not take the name and model number which is located on the furnace to your local hardware store. They will be able to look up the information for you and determine which furnace filter your furnace takes.
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