Here are a few opinions on the matter:
CPS Energy: "Check your air filter every month, especially during the summer and winter, and replace dirty filters that make your system work harder and waste energy."
Trane: "You should always double-check your owner’s manual for specific recommendations, but generally speaking it’s best to clean or change your filters once every 3 to 9 months. Remember, regular cleaning/changing of your filter will ensure the best filtration, increase the life of your machine, and give you peace of mind that you’re breathing easier."
Filtrete (filter manufacturer): "For maximum effectiveness, we recommend you change filters every three months. However, the life of a filter can depend on the individual conditions in your home. You may need to change your filter more often if your home has:
- Unusually dirty duct work
- Construction work in progress
- Furniture or drywall sanding in progress
- A fan running continuously
In these cases, you may want to change the filter more frequently."
Carrier: “Change the filters regularly”
US Department of Housing and Urban Development: "Change/clean filters on forced-air systems. Filters on individual forced-air systems should be changed or cleaned bi-monthly by maintenance staff. Disposable filters should be replaced using a type recommended by the equipment manufacturer, and permanent filters should be cleaned according to manufacturer's instructions."
Small Business Administration: "Replace air filters regularly"
Department of Energy: "Clean or replace your air conditioning system's filter or filters every month or two during the cooling season."
Energystar: "At a minimum, change the filter every 3 months."
The bottom line: Everyone has a different advice as far as how often you should change your filters. There is no correct answer because everyone has different homes and lifestyles. Here are just a few of the factors that can affect your filter change schedule:
- Number of humans and pets and the type of pets in the house
- How often humans and pets enter and leave the house
- Whether you have carpet or hard floors
- How often your home is cleaned
- Air leaks in your duct system
- Air leaking through from your home to the exterior (windows, doors, etc.)
- How much your system runs (can be affected by thermostat setting, outdoor temperature and energy efficiency of the home)
Check your filters weekly until they become until you notice they are to the point of needing to be changed. Do this through 2 or 3 filter change cyles and make note of the time between when you needed to change the filter so that you can determine what the right schedule is for your home or business.
Any major changes to any of the above mentioned factors or things like remodeling can change your filter change schedule. If you change the type of filter you are using you may have to modify your filter change schedule as well. The more efficient the filter is the easier it will be for the filter to become stopped up.
There are many digital thermostats that are available that can alert you to check your filter based on either a customizeable number of calendar days or even by the number of system run time hours. It will take a little bit of trial and error and note taking but if you can figure out about how many system run time hours your filter usually takes before needing to be replaced and set your thermostat reminder accordingly then you will have a pretty reliable filter change reminder whether your system is running non-stop in the summer or barely turning on in the fall.
If all of this seems like too much hassle to worry about, we don't blame you. There are several options available for large media air cleaners that install near your furnace or air handler. The replacement filters for these air cleaners last 6 months to a year in most situations and the replacement filter cost is usually less when compared to several changes of a super high efficiency 1" pleated filter. So if you have preventative maintenance performed on your equipment twice a year you can hand over responsibility for filter changes to your HVAC contractor and you won't have to think about it anymore.
More interesting articles on heating and air conditioning here.