Simple steps to keep your furnace clean and efficient all year long

Question: How often should I change my furnace filters?

Our furnaces have been running long and hard, during the cold weather. They have been re-circulating the interior air of our homes, and the filters, depending on their quality, have been helping to clean our air as it passes back through our furnace.

We need to clean or change our filters periodically throughout the heating season and cooling season, if we use air conditioners. To set a hard and fast rule, like once a month, does not take into account our various home cleaning levels, number of pets or how dirty our ducting and furnace are. A blocked or very dirty filter can damage the heat exchanger, shortening its life span, and make the system very inefficient to operate.

Our heating season typically starts out with a little use in the fall, and then into a few periods of time working hard around the clock, by spring we’re hopefully using it a few nights.

So the once-a-month rule is a good starting point. By August or September, we should look to see what condition the filter is in. We may need to start the season with a new one or clean the one we have. We should make a note on the calendar to check it once a month to see how fast it fills up. In older homes with dirty ducts and those with cats and dogs shedding, we may need to replace them monthly. If we keep a fairly clean house and have a newer system or one that has been recently cleaned and sealed, we may be able to go for two months during heavy use. So monitor a new filter to see how long it takes to change color. Most make it very obvious when the dust levels are high enough to block some airflow.

First we need to determine what type of filter we have. There are three basic types, a replaceable/disposable filter, a washable filter, or an electronic filter.

The basic replaceable filter, which costs about a dollar, only protects the equipment from large dust or animal fur balls. They do little in the way of filtering our air and tend to re-circulate dust with the heat. I always recommend spending more money on pleated paper filters, from $4 to $18 for better dust control. There are many brands out there and they use a paper filter medium to grab more of the finer particles. Typically, the more expensive the filter, the smaller the particles and the cleaner the air.

We can spend as much as $100 on pleated paper filters, but they need extra room to house them, yet they will typically last a season. They should only be installed in a very clean, sealed duct system and furnace.

But do keep in mind that the better the filter, the more important that we keep our eye on it as to not allow it to get so full of dust that it restricts the airflow. A very dirty filter will starve our system of air, cause it to run very inefficiently, as well as shorten the furnace’s life span.

There are several versions of reusable filters on the market — some more effective than others. The electrostatic, unpowered versions have tested well until they have been cleaned a few times and then their efficiency for fine dust particles falls short. Some washable filters are so basic that they protect the equipment but do little collection of dust that coats our furniture.

An electronic air filtering system is very efficient for grabbing dust, including the finer particles, but we need to also consider the ozone generation that is an undesired byproduct. People with dust sensitivities and respiratory issues should consult a doctor and consider a very efficient pleated paper filter, which doesn’t pollute the air with ozone as it cleans the dust. Definitely consider installing a HEPA filter system with an air-to-air heat exchanger if indoor air quality is important.

Electronic filters will require cleaning on the same schedule as the replaceable pleated filters. They can be hosed off, cleaned in a mop sink, or run through a dishwasher. But be very careful not to break the very fine wires, an expensive repair.

So check your filter or filters and get additional information and instruction, if needed, from your service technician. Some are tricky to reach until you’ve practiced a time or two, but after you’ve spent a season monitoring them, you can decide whether monthly or bimonthly works for your home. Always err on too often if you want to protect the lifespan and efficiency of your furnace, and don’t forget that the more you use the air conditioner — the same issues apply during the summer. We should be annually servicing the older gas and oil units; every two years for newer ones, and every five years for electric ones.

Most furnaces use two filters to clean the air as it keeps us warm during these cold winter nights. So buy several filters at a time and don’t forget to buy a carbon monoxide detector for each level of your home.


• Start by checking your filters monthly to determine a schedule for your home.

• Paper, electronic and washable filters follow a similar schedule.

• Pleated paper filters can lower the dust levels in the home.

• A dirty or blocked filter will lower your furnace’s efficiency and lifespan.

• Clean and seal your ducting for improved performance.

• Install carbon monoxide detectors.

Contact Steve at

We encourage an open exchange of ideas on this story's topic, but we ask you to follow our guidelines for respecting community standards. Personal attacks, inappropriate language, and off-topic comments may be removed, and comment privileges revoked, per our Terms of Use. Please see our FAQ if you have questions or concerns about using Facebook to comment.
blog comments powered by Disqus

Read the Oct 26
Green Edition

Browse the print edition page by page, including stories and ads.

Browse the archives.

Friends to Follow

View All Updates