![illustration of a hand replacing a white furnace filter in the blue wall next to a white outlet](https://img.livestrong.com/375/media-storage/contentlab-data/11/3/05fbcdfffe224ae2a36203e3f7f99dbd.jpg)
It’s a good rule of thumb to check your filter once a month during the heating (or cooling) season.
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How often to change furnace filters is a classic homeowner question. Technically the answer is every 1-3 months during the heating season. If you are far from this schedule or if you never change your furnace filter, there is a good chance that your indoor air is dirtier than it should be and your furnace is working harder than it needs to be.
A furnace filter has one primary job: to trap dust and other small debris to prevent them from getting inside your furnace. The filter also prevents dust and debris from blowing through your ducts and back into the house. In other words, it takes it out of circulation.
A dirty, clogged air filter doesn’t clean the air well and, even worse, it restricts airflow through your HVAC system. This means your furnace won’t heat your home as well as it could, will cost you more to operate, and will likely need to be repaired or replaced sooner than it should.
In my two decades of helping people repair and renovate their homes, I’ve seen some pretty serious cases of furnace filter neglect as well as costly consequences. Here are all the reasons why it is actually quite inadvisable to never change your furnace filter, or even not change it enough.
How Your Furnace Filter Works
To understand why it’s important to change your filter, it helps to know exactly what your furnace does. A furnace is a type of “forced air” heating system. It has a powerful blower motor and fan that forces air through the furnace, into the outlet ducts (called supply ducts), and through the heating registers to the rooms in your home.
Like all fans, the furnace fan does not create air; it simply moves air from one place to another. When it forces air into the furnace, it simultaneously draws air out of the house, through the incoming ducts (called return ducts) and returns it to the furnace.
All circulating air passes through the furnace filter just before entering the blower compartment inside the furnace. As everyone has noticed when watching the sun’s rays pass through a window, there are a lot of things floating in the air: dust, pollen, pet hair, etc. This is what gets stuck in the furnace filter.
Once a filter gets really dirty, it becomes more of a barrier than a filter, and dirty air can bypass it and enter the furnace. There, air contaminants collect on the fan motor and fan as well as inside the heat exchanger, where the air is heated before being sent to the supply ducts .
The combination of restricted airflow and dirty air decreases energy efficiency and increases wear and tear on the furnace – which, along with air conditioner, is probably the most expensive piece of equipment in your home. Buildup inside the oven is a common cause of overheating and oven shutdown.
Can a dirty furnace filter make allergies or asthma worse?
By trapping airborne particles like dust, dander and hair, furnace filters help eliminate common allergens and irritants in your indoor air. And because dust mites and mold feed and travel on airborne particles, a dirty furnace filter can make symptoms worse in two ways: it fails to capture particles and provides a food source for these irritants.
“Dirty filters should be cleaned (or replaced) regularly, as they can develop dust mites and mold, which can in turn cause allergies or asthma,” Purvi Parikh, MDan allergist/immunologist from Allergy and Asthma Networktells LIVESTRONG.com.
If you suffer from allergies or other conditions related to indoor air pollution, it is important to understand that a furnace filter cannot purify your indoor air; it simply helps reduce airborne particles, primarily to keep them out of the furnace and ducts.
The performance, or effectiveness, of filters varies widely (more on that below), but even the best furnace filters help purify your air only when the furnace is running.
In addition to regularly replacing or cleaning the furnace filter, “a HEPA (high-efficiency particulate air) purifier can help further purify the air of allergens, irritants, etc.” “, explains Dr. Parikh. “The bedroom is the most important room to keep free of irritants and allergens.”
It is also important to note that a furnace filter does not protect a home from carbon monoxide (CO), a deadly, odorless, colorless gas that is a byproduct of burning natural gas or propane, such as make most furnaces.
With a fuel (gas or propane) furnace, CO can enter a home through a cracked heat exchanger (where heat from the burners transfers to the air) or through a cylinder head or blockage in the exhaust duct of the furnace.
“A carbon monoxide detector should also be in every home,” says Dr. Parikh. At a minimum, every home equipped with a fuel-fired boiler or other appliance should have a CO alarm inside or near the exterior of every bedroom, depending on the International Residential Code (IRC).
How effective is your furnace filter? Check the MERV rating
A MERV rating is a number printed on air filters. MERV stands for Minimum Efficiency Reporting Value, and it basically tells you how well the filter captures particles – you might say how “fine” it is.
MERV ratings range from 1 to 16 for standard filters. The higher the number, the finer the filter. The Environmental Protection Agency (EPA) has a simple MERV Rating Chart which gives you the sizes and quantities of particles captured at each MERV rating level. There are also HEPA filters with MERV ratings of 17 to 20.
The topic of filter effectiveness can get quite technical and even controversial, but it really comes down to two questions:
- How well do you want to filter your air?
- What type of filter is best for your furnace?
Answering the first question may require a compromise. Filters on the higher end of the rating scale – MERV 14 to 16 – capture the most particles, but they can also be the most restrictive in terms of airflow, forcing your furnace to work harder and possibly limits circulation throughout the house. Those on the lower end of the scale — MERV 6 and lower — let air flow freely, but they also stop far fewer particles.
For many homes, a mid-range filter rated MERV 7 to 13 is the ideal solution. These can do almost as good a job at removing particles as a HEPA filter, depending on the EPA. But if indoor air quality is an important consideration for you or a family member, talk to a doctor about making your air as clean as possible. This may involve the use of more efficient furnace filters and/or the use of air purifiers or installing an HVAC filtration system.
Answering the second question is simple: check your furnace owner’s manual or contact the manufacturer to find out the recommended filter for your furnace model.
Tips for Replacing Your Furnace Filter
Checking and replacing the filter is an easy DIY job on most furnaces, but the exact steps to follow are specific to the furnace model. That said, there are some basic tips that apply to almost any furnace equipped with a standard filter.
First, turn down the heat or turn off the furnace at the thermostat so the system doesn’t start while you check or change the filter. And remember: check your furnace filter once a month and replace it if necessary (usually every 1 to 3 months).
Before installing a new filter (or reinstalling an old, sufficiently clean filter), make sure the filter is facing the correct direction: there is an arrow and the words “Air Flow” on the filter; the arrow should point towards the oven.
When purchasing filters, choose products with a MERV rating that is appropriate for your furnace and home environment. This may require a bit of research and experimenting with different filters.
Finally, don’t make the rookie mistake of buying one filter at a time. If you do, you’ll have to make a trip to the store every time you need to replace the filter, and chances are you’ll put it off and live with a dirty filter instead. It’s best to buy enough to get you through the entire heating (or cooling) season at one time.
So how bad is it really if you never change your furnace filter?
Never changing your furnace filter would be bad for your indoor air quality at best – and potentially catastrophic for your furnace at worst. Even changing the filter too rarely will lead you in the same direction.
In summary, here are five reasons why it is not recommended to change your furnace filter:
- Airflow is restricted throughout your HVAC system.
- Dirty air enters the furnace and ducts.
- Indoor air quality suffers.
- Your furnace experiences unnecessary wear and tear.
- Energy efficiency is reduced.
To avoid unnecessary problems, try following this simple rule about how often to change furnace filters: Check your filter once a month during the heating season and replace it whenever it becomes dirty. Do the same in summer if you have air conditioning.
Typically, a filter should be replaced every 1 to 3 months, depending on home conditions and how long the furnace (or air conditioner) has been in use, depending on Carrierone of the leading manufacturers of furnaces and other home HVAC equipment.
Try this pro tip: At the start of the heating season, buy five new filters. Put one in immediately before turning on the oven for the first time. You’ll start the season with a clean filter and have four replacement filters to get you through the winter.