A person sitting on a couch

The Best Way I Know to Slash the True Cost of Dirty HVAC Filters

Do I have a story to tell you—another lesson I’ve learned the hard way so you won’t have to. Truth be told, if my faux pas helps you avoid a huge expense, I’m happy to have suffered it.

While researching to help a reader solve the mystery of black grimy lines around the edges of his home’s carpet, I casually asked my husband if he’d replaced the filter in our heating ventilation air-conditioning (HVAC) system recently. I got one of those blank stares I could easily translate: Nope, didn’t even think about it.

When we bought this house, we had the HVAC system inspected, serviced and the filter replaced. Then we got busy with leasing it while we planned and executed our big move a year later. HVAC filter? Completely forgot about it. By the time I brought up the subject, it had been more than 2.5 years!

A close up of a sign

The scariest thing ever was to open that door on the HVAC system, dutifully labeled “Filter.” I cannot adequately describe it but I can tell you that it was nearly black and covered in what looked like fur. So gross. I’m surprised the entire system didn’t just blow up out of sheer rebellion for lack of attention.

I have since learned about the true cost of a dirty HVAC (heating, ventilation, air-conditioning) filter and it’s not pretty!

The True Cost

High energy bills

While the heat, ventilation or air-conditioning is running, 100% of the air in your home passes through a filter, typically twice every hour. When the filter is clean, the air passes through easily. But if the filter gets clogged up with all the stuff it’s filtering out, the system has to work much harder to keep air moving.

The dirtier the filter, the less efficient the system can be—and more likely to develop problems. According to the Department of Energy, regular filter changes can reduce your energy bill by 5% to 10%. Conversely, a dirty filter will send that bill through the roof!

Family health

A quality filter captures the harmful bacteria typically found in sneezes, coughs, viruses and molds, as well as pollutants like dust and car fumes that come in through doors and windows.

If you have allergies or asthma, indoor air pollution can trigger your symptoms. Most people don’t realize that indoor air pollution levels are actually much higher than those outdoors—two to five times higher, according to medical professionals.

When particles become airborne, you can breathe them in and experience an allergic reaction. The heating, ventilation, and air conditioning (HVAC) system in your home can harbor and then spread mold and other allergens.

Grimy, dark carpet stains

It’s called filtration soiling and shows up as dark, shadowy, dirty lines on the carpet along baseboards, under doors, beneath draperies and along the edges and in the crevices of carpeted stairs.

A close up of a door

Filtration soil is as ugly as it is gross and comes from airborne pollutants passing through the carpet as the air is drawn through the crack between the carpet and the baseboard, around the drapes or under a closed door.

It’s an accumulation of soot from dirty ducts, smoke from candles and the fireplace; tobacco, kitchen grease from the oven and cooktop; smog, auto emissions, and pollutants from outdoors.

The way it’s supposed to work is that all of that stuff in the air gets trapped in the system’s air filter. But once the filter is full, the system will send the air pollutants back into the house through the ducts where all of that icky mess gets lodged into corners and crevices.

MORE: Grimy Black Filtration Stains and How to Get Rid of Them


The Simple Solution

Change the filter often

Check at least once a month, more often during heavy use months (winter and summer). Keep in mind that some systems have multiple filters. Take some time to research your system to discover exactly what and how many filters you have.

If the filter looks dirty after a month (it is no longer white) change it. Homes with pets, multiple occupants or when located in regions with general air pollution, may require more frequent changes. At an absolute minimum, the filter must be changed every three months,

A dirty filter will slow down air flow and make the system work harder to keep you warm or cool, wasting energy. A clean filter will also prevent dust and dirt from building up in the system leading to expensive maintenance and/or early system failure.


Mark your calendar. Set an alarm. Do something that will trigger your memory to check your filter so you can get to the store to buy a new one. Or a bunch so you have them on hand.

Don’t assume you’ll just remember. You probably won’t until one day, 2.5 years from now you notice your utility bill has shot through the stratosphere, you have this weird cough or you see odd, dark shadows forming along the edges of your carpet. Don’t let that happen.


My filthy filter wake-up call prompted me to get online to do some research. That’s how I found Second Nature (formerly FilterEasy), a company that delivers the exact filter we need, just when we need to change it—at a comparable cost of the very same filter at the home improvement center store near our home. Wow! What a great service for those of us who need reminders. I don’t have to think about when to replace the furnace filter.

I set up an account online, identified the exact filter we need (they’re listed by size—including custom sizes if the filter you need is not standard) and the frequency of delivery, which took all of about five minutes. Now I can forget because I’ve put Second Nature in charge of remembering.

We received our first shipment. Having that sizable box show up at the door was the reminder we needed to replace the filter—right then. Done.

You can probably beat the FilterEasy price if you buy filters when they’re on sale and are diligent in sticking to your own rigid maintenance schedule. For some of us, a subscription plan with Second Nature  is a real bargain given the high cost of failure to stay on top of this important home maintenance issue.

The folks at Second Nature are offering Everyday Cheapskate readers their first set of filters free (you’ll just pay to ship) when you use this LINK. Of course, you can cancel or make changes to your subscription at any time.

Some products displayed in this post may earn us a commission. Why trust us?


More from Everyday Cheapskate

cleaning supplies: cleaning spray bottle with plastic dispenser, protective gloves, sponge
bowl of homemade soup
box of emergency food
modern closet with clothes hanging on rail, white wooden wardrobe, interior design concept
Instant Pot with Beans Rice and Fresh Vegetables
cropped view of girl with blanket warming up with heater in cold room
Ceramic Bakeware, Ovenware. Bakery Kit. Ruffled Pie Dish

Please keep your comments positive, encouraging, helpful, brief,

and on-topic in keeping with EC Posting Guidelines

Print Friendly, PDF & Email
13 replies
Newer Comments »
  1. Cathy Sage says:

    Kudos, Mary. Wow, have you done a real public service here. I just asked my husband when the filter was last changed! He said, “Uh oh”! I told him to please show me how to do this. We went down into the basement of our old farmhouse and it took all of 30 seconds. The blue filter was very dusty but at least it wasn’t growing hair. How simple. Our filters in Florida were horrific. Not sure if it was our fault for not changing or if it was just a dustier area. Those grew hair! This is so simple, even a monkey can do it! Thanks, again. Will mark the first of the month as a time to do this.

  2. ThistleCoveFarm says:

    There are 4 filters in the house – 3 bedrooms and 1 in the hall. Does the actual heater have a filter as well?

    • Mary Hunt says:

      It may, but not necessarily! Should be fairly easy to look if you have easy access to the furnace area. Otherwise a Google search for that particular brand/model can turn up an owner manual that should give you that information.

  3. Joni Kelly Lmt says:

    Hi Mary, I can testify that changing the filter often pays off! When I moved into this house I was not accustomed to an HVAC system at home (only at work) and took the word of the former tenant that the filter had been changed. He was also a smoker and I spent every day trying to rid the house of cigarette smell. I have cats so I already knew I’d be changing the filter frequently, but I was appalled to find the last tenant used a folded 16″x25″ in the space for a 16″x20.” When I changed the filter, it helped a little, but it wasn’t till the AC man I had hired for my office came to my home. When he cleaned the dog fur, cigarette smoke saturated, A-coil the house took on a whole new smell. A delightful clean smell!

    I now have my calendar marked for 3 week intervals since I work from home and still have cats. Clients are always amazed when they see cats and yet don’t smell cat odors. (Of course, I also clean with Nok-Out to be extra sure!) Oh, and my electric bill is so low, I’m going to negotiate a different, lower energy use contract this year!

  4. Joanne Hansen says:

    Hi Mary. You are so right to send this reminder. Changing the furnace filter is about the only thing I know how to do. I change it every October 15th before the furnace goes on. Two weeks ago, right before I went to bed, I smelled something (like when a hair dryer overheats) coming from the vents in two bedrooms. I was afraid, so I turned down the thermostat to turn off the heat, and “Googled” quickly. Said it could either be a dirty filter or worse, the blower. I changed the filter and it was filthy (after only 4 months), but I was still apprehensive about turning the heat back on until the furnace was checked by a professional. When the technician came the next day, he found nothing wrong with the furnace. Turned it back on, and no smell. So I believe it was the filter causing the smell. I’m sticking with the every-three-months schedule from now on!

  5. Beck says:

    Our furnace technician said the same thing change filter monthly plus use lower Merv rated filters a/k/a the cheaper fiberglass ones..so it doesn’t overwork the furnace. We change them monthly. Try buying in bulk at Menard’s when they do the 11% rebate and you will get one free or almost free with the rebate. Put it on your planner the first day of each month. Septic treatment can also be done the first of each month to keep that system running smoothly as well.

  6. Marla says:

    We had a heating and air guy (who we trust) tell us that the cheap air filters were the best provided you change them regularly (he said at least every 2 months). He said the cheaper ones allow more air to move through the system than the more expensive, tighter weave filters. His one caveat that he repeated numerous times was that you have to be diligent about replacing them. I set an alarm on my phone calendar. I also write the date that I changed them on the cardboard rim of the filter just in case my calendar malfunctions or I happen to notice that it needs to be replaced before the calendar alarm goes off.

  7. Patti Karr says:

    Guilty!!! Checked mine about 6 weeks ago when I had to have the water heater replaced. I live in a mobile home and the furnace and water heater sit side by side and are accessed outside. Because there is a reallllllllllly heavy panel with screws that has to be removed to access it, I hadn’t checked my filter for at LEAST a year. Once inside the “closet”, you have to remove another panel with screws on the furnace to get to the filter which makes it even more unlikely to check it very often. My filter is a green meshy type of thing with no frame that is washable. It was BLACK and damp…like mold? So it has to be hosed off and then put in the sun to dry. I sped it up by using a hair dryer this time. It’s also really difficult to get it back in place. There must be a better way?!

  8. B Johnson says:

    I buy my filters at the nearest warehouse membership store, three at a time. I get paid once every month, and I use that date as the trigger to replace my furnace filter. Since I live in a house with four people with allergies, and four cats (luckily none of us are allergic to cats), changing the filter every month is a necessity (even though the owner’s manual recommends changing the filter every three months).

  9. Alyson Tanner says:

    I find your HVAC filter solution extremely expensive. For the cost of 1 month’s normal price ( about $23 in my case) worth of filters I can buy one whole year’s worth of HVAC filters at Lowes or Home Depot. I schedule the dates I want change to filters in my calendar and that does not cost me a dime. Cost of your filters $23 x 4 = $93/yr vs the cost of my solution $19.43/yr

Newer Comments »

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *