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 send your energy bill skyward and potentially contribute to other maintenance issues down the line. The good news is that figuring out the best rate at which to change your air filter is actually easy, and this article will help you do exactly that.

General Recommendations

So, how frequently should you change your air filter? The answer is, "it depends,” as it will change depending on where you look. 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 you see a recommended interval at which to change your air filter - perhaps every 4-6 weeks, or every 30 days - 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. These can include:

- The rate at which you use your heating and/or cooling system. If you live in a 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, however, you might need to change your filter every few weeks (especially if you're using a cheaper fiberglass filter).

The size of your home. Furnaces and air conditioners in smaller homes need to pump less air for the same amount of temperature change, which may translate into less frequent filter changes; these appliances, though, are also often built with smaller filters and thus may need to be changed just as regularly.

- The air quality within your home. The air within or outside your home will also affect your filter's replacement cycle. Pets, for example, or 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 four 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.

Facts Surrounding Dirty Filters

If you understand what air filters do and why they're so important in your HVAC system, you'll have no trouble understanding why dirty filters are such a problem.

The air around us is perpetually filled with dust, dirt particles, and other "contaminants." 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, they just make 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 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 won’t heat or cool your home efficiently because it will end up staying on longer and working harder to try and reach the temperature at which your thermostat is set. 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 its job removing dust and other particles from the air in your home and thus  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.  If you can change your air filter before it becomes completely clogged, the air will continue 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.

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 your filter has trapped too much dirt and needs to be replaced?  

There's no strict guideline, but if your filter shows only a subtle layer of dirt under which the filter’s  material is still visible, your filter is in fine working order. Once it gets much beyond that point, it's ready to be changed out. If there's a visible coating of dirt covering most of your filter's surface that is adequately thick to obscure the filter material itself, that's a sign that your filter has been in your HVAC system far too long.

If in doubt, it's always best to err on the side of replacing your filter. They're relatively inexpensive, and that small cost to keep your heating and cooling vents clear will be well worthwhile when your energy bill comes due. If it's been a while since you've changed your filters, 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!