If you live in a home that has central heat/AC or if you have a car, then you have air filters.  And if you haven't changed them for awhile, then chances are your systems are using more energy than they need to and hurting their performance.  For most homes and cars, changing your air filters about every 3 months will do the trick, but you can do a visual check to see if you need to change your filters more or less.  Why do you need to change your filter?

Think of it this way: Have you ever tried to exercise with something blocking your nose or mouth (think playing in the snow with a ski mask)?  It was probably harder to breathe wasn't it?  Your body had to work harder to ensure that your lungs had enough air to keep your body moving.

When an air passageway is blocked with something, whatever moves the air through the air passageway  (some form of machine) has to work harder.   In your body, that machine is your muscles and lungs, in your home that machine is the furnace's fan that pulls air through your home, and in your car it is the engine and air intake system.

Your home's furnace and your car's engine don't like dirty air (neither do you), so they use a filter to prevent debris from entering.  If this filter is blocked, your house fan or car engine has to work harder/longer to do the same amount of work as if they had a clean filter; which means you are using more energy!  Actually, you have a filter too: Your nose hairs!  That's why you should always breathe in through your nose and out the mouth; so your nose can filter the air before it hits your lungs.

Change your home filter:

1. Go to your central heating/cooling system. (some filters could be located at another point in the air intake system)
2. Look on the side of the furnace and you should see the location of the air filter (it may have a sheet metal cover over it)
3. Check the size of your air filter (my filters are 16 X 20)
4. Pull out the air filter and see if it is dirty (the best way to do this is have a clean filter handy to compare the dirty one to)
5. If it's dirty, change it

Filters could cost around $3-$5 bucks.  There are real expensive filters for people who have allergies, but most homes can go with the basic models.  For instance, the brand of filters I get is NaturalAire and Home Depot has a 3-pack for $6.48.  Buy a couple 3-packs and keep them near your furnace.  It makes changing them much easier when you have them on hand!  Put a note on your calendar to change your filter every 3 months!

Change your car or truck filter:

Edmunds.com has a nice article about changing your auto's air (and fuel) filter.  In regards to the air filter:

Next, check it for cleanliness. Hold it up to the sunlight and (while keeping it at arm's length from your face) bend it back, so the paper ridges of the filter flutter like the pages of a book, and look inside the crevices. Do you see a lot of accumulated dirt and grime? Now look at it straight on. Is the orange or yellow paper mostly dirty in the center? If so, then you should replace it. No big deal — the replacement only costs about $10-15.

They also mention that the place that services your car will try and hit you up for over $20 to do the same thing that you can do for yourself much cheaper.

1. Go to the auto parts store and tell them you need an air filter for your make/model of car/truck
2. Mine usually costs around $12-$15
3. If you don't know how to change the filter (see the above Edmund's article, ask the auto part store employee)

Changing your car's air filter is one of the easiest and cheapest maintenance jobs out there and it can improve your mileage and help your engine breathe better.