What You Need to Know About Furnace Filters
Maybe it is on your to-do list, or maybe you’ve thought about putting it on your to-do list… If replacing your furnace filter is not part of your regular home maintenance, though, it should be. This is one of the simplest, low-cost steps you can take to protect one of the most important investments in your home.
How a Furnace Works
While there are different models, most furnaces work by drawing in air from return ducts throughout your home, warming it over a heat exchanger, and then blowing the heated air with a fan through ducts that open into the various rooms. This is known as “forced-air.”
What a Furnace Filter Does
When the air comes into the furnace through the return ducts, it typically carries with it dust, hair and other debris. The purpose of the furnace filter is to keep all of that dirt from collecting in the blower fan. This has several benefits. It prevents damage and excess wear on your furnace; it helps keep your furnace running efficiently; and it keeps all that dirt from recirculating in your home, reducing allergens and improving your indoor air quality.
The furnace filter is only effective until it becomes full, however, so to keep your furnace, functioning properly, it should be replaced with a new one every 1-3 months, depending on the type.
How Filters are Rated
Furnace filters are rated on the MERV (minimum efficiency reporting value) scale, which runs from 1-16. The higher the rating, the more particles the filter will trap. Higher ratings aren’t necessarily better, however. The highest rated filters may not allow enough air to flow through and can make your furnace work harder (less efficiently). Most furnaces work best with a filter rated between 8 and 11. Check with your furnace manufacturer to determine if your model has a recommended maximum MERV rating.
The most common filters are the disposable, pleated variety. These are made of paper and polyester. They vary in price from a few dollars up to $40, depending on the rating, size and brand. Pleated filters should be checked monthly, to make sure there are no blockages, and replaced every 3 months.
Another type of disposable filter is made of fiberglass. This is the cheapest, but also the flimsiest. Fiberglass filters have the lowest MERV rating and should be replaced monthly, so consider that when you are pricing them against longer-lasting pleated filters.
Permanent reusable filters are expensive, but last up to 5 years with proper cleaning (every 3 months). Also called washable filters, they have either an aluminum or plastic frame and are more efficient than disposables. Clean them with a vacuum and water.
Both disposable and permanent filters are available in electrostatic versions, which self-charge as air passes through them. The charge allows them to collect more particles. Homes with pets or smokers can benefit from electrostatic filters. Make sure that they are safe to use with your particular furnace.
Furnace filters are sized by thickness, height and width. Check the old filter for the size (typically printed on the frame) before buying a replacement. If your furnace takes a custom size, check with the manufacturer for where to purchase.
How to Replace Your Filter
Replacing your furnace filter is simple, but it helps to do a little preparation. First, turn off the furnace while you are changing the filter so it doesn’t turn on during the process. Next, have a trash bag ready for the old disposable filter, as it will come out full of dust and dirt. Then open the filter compartment door (between the air intake and the furnace), and slide the old filter out. If you have a permanent filter, vacuum it off before cleaning it thoroughly with water and let it dry completely. Vacuum the outside of the furnace and around the filter area if it is dusty before inserting the new filter. Look for the arrow on the filter that indicates the direction of airflow. The arrow must face the furnace side of the compartment to work properly. Slide the new/clean filter into the compartment and restart the furnace.
Check your furnace filter every month, and replace it (or clean it) every 3 months. Doing so will help keep your furnace running properly, reduce the risk of breakdowns, and keep your energy bills low.