How often should I change my furnace filter?
This is easily our most frequently asked question, and the answer is, it depends. As your air filter loads with dust, it restricts air flow, making your furnace work harder. This runs up your electric bill and decreases the life of your entire comfort system. Most filters come with a replacement recommendation (like every 3 months), but the actual life of the filter will vary widely based on application. These four factors effect the life of your furnace filter.
- Furnace Size
- Filter Size
- Filter Type
- Dust load in the home
A large home needs a large furnace, and a large furnace needs a lot of air. A 120kBtu furnace moves twice as much air as a 60kBtu furnace, which means the filter will get dirty twice as fast.
Hey, this isn’t rocket science. A larger filter holds more dust. A typical 20x25x1 filter has nearly 30% more surface area than a 16x25x1 and, therefore, 30% more dust holding capacity. You can’t really change your filter size, as it needs to fit the rack that was installed with your furnace. However, you should take this into account when deciding on a filter schedule.
We typically judge a furnace filter’s effectiveness by looking at it’s MERV rating. Click here for the nerdy explanation. This rating ranges from 1 to 16, with the higher number indicate more allergen removal. The problem is that, while a MERV 16 filter stops very fine dust, it also stops air and can cause furnace overheating and A/C freeze-ups. A high MERV filter will load with dirt sooner, and will need to be replaced more frequently.
Dust load in the home
Much of our house dust comes from living activity, and more people equals more dust. A family with large, hairy dogs can expect large, hairy furnace filters. On the other hand, if you live alone, don’t smoke, keep a tidy house, and you don’t have a furry friend, you can easily double your filter life.
In most cases, one-inch thick furnace filters need to be replaced every one to two months, no matter what the packaging says. In just over an hour, our technicians can work a little duct magic to replace your 1-inch filter rack with a real air cleaner. An Aprilaire filter has four-inch deep pleats to allow great airflow to your furnace. With a dust-holding capacity of more than a year, filter replacement is actually cheaper and much less hassle than a monthly trip to the hardware store.
Still have questions? Check out our page on Indoor Air Quality. We address the four main factors in a home that contribute to allergy symptoms.