The Ultimate Guide On Furnace Filters

Furnace filters are an often overlooked part of basic home maintenance.

When I perform home inspections, I am not surprised when I discover filters that are months overdue on cleaning or replacement.

Even though most 1-inch filters can be changed every 3 months at the longest, it still comes down to allergy sensitivity and personal preference. In my home, I change my filter at least every 30 days otherwise I start to sneeze and feel terrible.

In this guide, I will go over…

  • My #1 top picks for the best washable & reusable furnace filters
  • Signs to know when to change your A/C filters
  • My review on the best furnace filters specifically for allergy sufferers
  • Where your air conditioner filters are usually located
  • The best HVAC filters for odor removal
  • How to clean furnace filters
  • And lastly, my review on the best furnace filters for dust control

Let’s get started with this guide!


What's In This Guide?

Many of my clients don’t realize that there are washable furnace filters that can be cleaned every 1-3 months and reused.

These washable furnace filters are also treated with an electrostatic charge so that fine dust particles are attracted to the filter — while it allows clean air to pass through.

It doesn’t take an accountant to realize that buying a washable furnace once can save some serious cash over the years.

The average washable furnace filter will last between 3-5 years, but some can last 10 years or longer.

And the cleaning process is simple. All you have to do is take it outside, hose it off, and allow it to dry. You can also rinse it under a utility sink.

If you are tired of dishing out money each month for your HVAC air filters, then buying a high quality washable filter may be your ticket to savings.

However, if you or your family suffers from allergies, I personally still recommend buying disposable and high MERV rating filters specifically designed for allergy sufferers. Here is my detailed review on the best rated washable furnace filters.

Everyone knows that we have to change the furnace filter (at least most people), but when exactly should you change it?

My preferred method of changing it is based on a visual inspection of the filter, as well as your own allergic symptoms.

If you are sneezing and coughing at week 5, should you really wait the maximum 3 months manufacturer recommendation?

Also, HVAC filters are frequently installed incorrectly. One of the most important things is to have the arrow on the filter in the correct direction — towards the furnace air flow.

Besides the arrow, I find many filters are not properly sealed. There is a missing filter cover, which reduced the efficiency of the furnace.

Sometimes, I find a filter that is warped inside the furnace because the slot isn’t snug. If your furnace filter isn’t working properly or is never changed, it can literally cause an HVAC system failure.

Even though these things are simple to fix, changing your filter at the correct time and in the right way can make a big difference to your indoor air quality — and the efficiency of your HVAC system. I invite you to read my full article on how often to change a 1-inch furnace filter.

Many homeowners don’t realize that the quality of your AC filter can have a tremendous impact on seasonal allergies.

The basic filtration rating system for furnace filters is from MERV 5 and up to MERV 16.

As a home inspector, I recommend buying a filter that has higher than average MERV rating if you suffer from allergies — it can make a big difference to your air quality.

However, you need to be careful in going with a too high MERV.

The simple answer is that it may damage your furnace because it reduces air flow. Especially if you have a newer high efficiency furnace that has PVC exhaust piping.

If you install a MERV 13 or higher, it may cause harmful short cycling of your HVAC system (rapidly turning on and off). I think MERV 8-12 is high enough for most allergy sufferers, and is already superior quality to the average HVAC filter.

I also recommend changing the filter every 30 days if you suffer from allergies, or you can also wait until you start to get allergic symptoms but before the 90 day manufacturer maximum recommendation.

To read my full article on the best air conditioner filters for allergies, you can read it here.

where is my furnace filter located (1)

When I inspect homes, once in a while, it can be a challenge to find all of the furnace filters — and it may be downright impossible for a new home buyer.

Furnace filters should be in one of two places — at the furnace (air handler) or the return vents.

With some homes, there are 4-5 furnace filters in multiple large return vents (sending air back to the furnace through the return duct).

However, once in a while, there aren’t AC filters in the return vents or at the furnace. Unfortunately, with these filters, the likely location is inside the furnace — which means you will have to take off the cover.

Some furnaces covers are pretty easy to take off, you just loosen a few knobs and it is removed.

With other filters, they can be a little tricky. You will have to remove some hex screws, and you may even have to remove the top and bottom furnace cover.

If you would like to read more on where to locate the furnace filter, you can check out my article here.

If your house has some smelly odors such as from pets, cooking, household cleaners, or smoke — then these specialty filters are for you.

These filters contain charcoal granules inside of the filter to capture odors as well as filter the air.

Carbon filters have a high surface area — they contain many crevices — and these pores literally catch the odor molecules as they pass through the furnace filter.

These filters generally have a dark or black appearance to them in contrast to the normal white colored HVAC filter. 

In addition to these carbon containing filters, the manufacturers sometimes include additional odor fighting ingredients like baking soda and other proprietary substances — such as the deodorizing filter made by Arm & Hammer.

The fact that charcoal catches smelly odors isn’t anything new. In fact, ductless range hoods already contain a charcoal layer and it is also used in many other products.

If you would like to read my full article on the best rated furnace filters for odors, you can check it out right here.

You can’t clean disposable filters — except in rare cases when there is large particles debris — you can just vacuum it off.

However, there are filters that can be regularly cleaned and reused such as washable furnace filters and electronic air cleaners (commonly called EACs).

These furnace filters need to be regularly cleaned such as every month for washable filters and about every 6 months for electronic air cleaners.

Reusable furnace filters can be a great strategy for saving money and keeping your indoor air quality at a high level. 

In fact, there are few furnace filters that can match the efficiency and filtration levels of an electronic air cleaner. Unfortunately though, if you forget to regularly clean these filters, your indoor air quality is going to plummet.

To get more info on how to clean an AC filter, you can view it right here.

Some homes just get a lot of dust.

Whether you live in a dusty area of the country, maybe you live next to a dirt road, or you have a lot of pets — cleaning household dust can become a nuisance.

If you are tired of sweeping and dusting your tables, then buying a furnace filter that will help reduce indoor dust is your best bet.

In order to control household dust, I recommend buying a furnace filter with at least a MERV rating of 11.

MERV (minimum efficiency reporting value) is a widely accepted filtration rating. Basically, the higher the MERV rating, the more particles it will filter from your air.

On the low end of the spectrum, you have the non-pleated fiberglass filters. These have a MERV rating of only 4, and I definitely don’t recommend these poor quality filters.

In addition to a higher MERV, you also want an AC filter that is pleated (accordian style) because it will have a greater surface area and will catch more dust. To see my article on the best rated furnace filters for dust control, you can check out my guide right here.

What's The Bottom Line?

Furnace or air conditioner filters are an important part of having a clean and healthy home.

The most disgusting homes I ever inspected were homes with extremely dirty filters — maybe that haven’t been changed in over a year. The occupants literally had no idea that you even needed to change the filters.

It is hard for me to fathom what it is like to live in a home with such terrible air quality. Frequently, these homes with poorly maintained furnace filters result in other issues like…

  • Mold growth around vents and inside the furnace
  • Poor cooling and heating capacity
  • And allergic symptoms and respiratory diseases

Don’t let your home become one of these ugly situations.

Just choose the right filter, and change or clean it frequently.