Summary: Before you buy a replacement furnace filter, there are 3 things you’ve got to know.

If you’re shopping for a replacement furnace filter, congratulations! You’re already one step ahead of all the people who let their filters sit for far too long.
That being said, though, there are 3 things you need to know about that filter replacement you’re about to buy:

1. They can’t be re-used
As much as you might want to save some money, this isn’t a way to do it. Once your furnace or air conditioner filter is full of dirt and grime, there’s no going back. No matter how hard you try, you’re never going to be able to get it clean enough to use again. Instead, you’re going to have to get a brand new replacement furnace filter.
Luckily, none of these filters are very expensive, so it’s a purchase that any homeowner can afford to make!
And, remember, if you think you’re saving money by leaving your filter in longer, you’re not. In fact, you’re actually costing yourself money! That’s because your furnace and air conditioner have to work harder to compensate for a filter chock full of gunk. In the end, you’ll wind up paying much more for the extra utilities than you would for a replacement furnace filter!

2. There IS a wrong way to do it
Even if your replacement furnace or air conditioner filter is shaped like a perfect square, it is possible to install it improperly. In fact, the most common mistake comes from people who install their replacement furnace filter backwards. Unfortunately, if you make this mistake, it won’t work like it’s supposed to.
Luckily, though, it’s easy to avoid making any installation mistakes. That’s because every filter comes with special markings on it, so that you (literally!) know which way is up. As long as you keep your eyes peeled, there’s no way you can get it wrong!

3. Just because you love a certain brand doesn’t mean you’ll be able to use it
Since your replacement furnace filter has to fit exactly right, you have to opt for the brand that gives you the exact dimensions you need. Luckily, most of the big brands are made in the most common sizes. However, if you need an odd filter size, you may not be able to use the exact brand you want.
For example, if you love a Filtrete filter – but it’s half an inch too small for your furnace – you can’t use it. After all, that half an inch of extra space would leave a gaping hole and make a huge mess! Even the best Filtrete filter couldn’t make up for that!

Want to get the most bang for your buck? You’ll get it from the team at