How Often Do I REALLY Need to Change my HVAC Filter?

Replacing the filter in your air conditioning and/or heating system is an important part of keeping your appliances working properly and keeping your energy bills low. It's also a task that many homeowners forget about for months at a time, which can end up costing you on your energy bill and potentially contributing to other maintenance issues down the line.

Depending on the sources you check, you might find a wide range of recommendations for the frequency of changing your air filter. Typical recommendations range from every 30 days for cheaper fiberglass filters (which often don't do a great job of filtering), to as long as six months for higher-end pleated filters. When your filter sees heavy use, though, they should be changed more frequently; similarly, if you aren't using your furnace or air conditioner frequently, you might not need to change your air filter as often as your appliance maker or filter provider recommends.

So, how often should YOU be changing your air conditioner and/or furnace's air filter? The answer is, "it depends." Figuring it out is easy, though, and this article will help you do exactly that.

HVAC Air Filters Need To Be Changed When They're Dirty

If you understand what air filters do and why they're so important in your HVAC system, you'll have no trouble determining when they need changing out. Here's the nitty gritty on why dirty filters are such a problem.

There's dust, dirt particles, and other "contaminants" in the air around us, everywhere and all the time. It's just a natural part of the way the world is. Unfortunately, these solid particles don't play nicely with furnaces and air conditioning units, and it's no fun having them blown in your face and stirred around whenever you turn your HVAC system on.

Too many particles flying around in your home can contribute to allergies, congestion, and other health problems, in addition to just making things dirtier.

The air filter in your furnace/air-conditioning system is there to catch the majority of the particulate matter before it reaches your vents, letting air through but keeping the dirt held tight so it doesn't invade your home or disrupt your appliance's proper functioning. Tiny gaps in between the filter's fibers let the air flow through, while the fibers themselves grab onto the particles as they fly by.

Over time, though, those tiny gaps get clogged by all the trapped dirt and dust, making it increasingly difficult for the air to get through. If the air isn't coming through, your HVAC system isn't doing an efficient job of heating or cooling your home, and will end up staying on longer and working harder to try and reach the temperature set at your thermostat.

That means higher energy bills and a less comfortable home—a lose-lose situation.

A dirty filter isn't a bad thing, though—it means the filter is doing it's job removing dust and other particles from the air in your home, helping you breathe easier and keep things cleaner. Pleated HVAC air filters tend to work much better than lower-quality fiberglass filters in this regard, trapping more dust while still lasting longer before they become coated with dust and dirt and need to be replaced.

Changing your air filter before it becomes completely clogged with dirt keeps the air flowing nicely. When your filter's fibers still have plenty of gaps between them, your air conditioner and/or furnace is able to do its job unimpeded, pumping air into your home with ease while the fresh filter keeps it clean.

When you see a recommendation to change your air filter every 4-6 weeks, or every 30 days, or over any other specific time interval, what you're seeing is an estimate of when the filter will start to become clogged. This estimate assumes average use and will take into account the type and size of filter you have in place.

While these estimates make for good rules of thumb, there are a number of factors that can affect your HVAC air filter's lifespan. The amount you use your heating and/or cooling system is usually the most important; if you live in a relatively temperate climate and only use your heater for a few hours in the morning and/or your air conditioner for an hour or two in the afternoon, a single filter might last you a whole season or even an entire year. If you're running your HVAC system on a near constant basis most months of the year, you might need to change your filter every few weeks—especially if you're using the cheaper fiberglass filters.

Furnaces and air conditioners in smaller homes need to pump less air for the same amount of temperature change, which may mean filters need to be changed less frequently, though these appliances are also often built with smaller filters and may need to be changed just as regularly. The air in and outside your home will also affect your filter's replacement cycle—pets and poor air quality will require you to replace your air filter more frequently.

When in doubt, just pull out your filter and give it a look. You should be doing this at least every 4 weeks during periods when your furnace or air conditioner is being used regularly. If it's been awhile since you turned your HVAC system on, check your filter before you adjust your thermostat.

How to Tell When Your HVAC Air Filter Needs Changing

Any use will lead to some amount of dirt being trapped in your air filter—that's its job, after all. So how do you know when it's too much dirt and your filter needs to be replaced?

There's no strict guideline, but if there's a visible coating of dirt covering most of your filter's surface, in a layer thick enough that you can no longer see the filter material itself, that's a sign that your filter has been in your HVAC system far too long. A working filter might look like a piece of furniture in need of a good dusting—a coat of fine particle where the underlying material is still very much visible. Once it gets much beyond that point, it's ready to be changed out.

It's always best to err on the side of replacing your filter; they're inexpensive, and keeping your heating and cooling vents clear will be well worthwhile when your energy bill comes due. If it's been awhile since you've changed your filters out, we can help you find the right size, brand and type of HVAC air filter for your furnace and/or air conditioner—click on over and get your system back to clean efficiency!