Filter life expectancy

How often do you guys recommend filter replacement if they are the cheapy disposable filters. I usually go with monthly replacement recommendation. This filter that I found at yesterdays inspection far exceeded a every 30 day replacement.


I advise that they stop purchasing the useless filters and only buy the pleated ones.

It depends on the living situation. And how often they run the HVAC.

I have dogs, so my filters get dirty quicker than if I had no dogs.

I have a buddy who lives in a big house by himself. And he’s almost never actually home. His filters last him much longer than mine do.

I inspected a beach house the other day. There was no AC installed. And due to it’s proximity to the beach and location in Southern California, I doubt they run the furnace very often either. They only NEED a filter a few months out of the year.

Filter replacement every three to six months in my opinion for pleated MERV8 unless unit utilizes more efficient filters.

I recommend holding the filter up to a light if you can see the light don’t change it, if you don’t see the light change them. It takes the time factor out of the equation;-)

Filter replacement cycles depend on local conditions and time of year.

Charley has it right. Look for the light.

I’ve always used the flashlight trick on the air filters for my vehicles. It also makes sense to me that this would be equally effective for HVAC filters. In any event the filter pictured was definitely in dire need of replacement.

For the better result of your furnace you should be cautious about its maintenance. You must examine the conditions of its filter once in a month. If you are using cheap filters, it will be better for you to change it after every month otherwise it will effect your health and it also consume much electricity. We all know for what purpose these filters are being used in furnace, it is for controlling dust particles, pollen and other allergic related particles. It is therefore recommended cheap filters should be replaced once in a month.
Wherever you have found filter of such type which is far exceeded 30 days, it might be the user not used his furnace since long.

Every 30 days depending on how dirty the home is. I have seen homes where I recommend every two weeks.

If you are using cheap filters it is better to replace the same between one month to two months as you are already doing. If you use High Effieciency Pleated filters its result will be better in terms of catching dust partilces and other allregens particles. And they are properly washed within two to three months its life expectancy will get increased and provide you with fresh air.

It mostly depends upon the usage. If you are continuously using it, in such case it is to be replaced after one month or maximum within 2 months. On the other hand if you are using HEPA filters, it is washable and to be washed after one month or two. It needs replacement after 5 years.

This is odd.

I just started stating that they should check them on a monthly basis and replace or clean(washable) if needed.


Wow! Misinformation abounds on this subject matter!

I am not going to try to persuade anyone’s perspective with actual data because this subject will be way too time-consuming for anyone to even start reading.

A few points to consider:

A 1 inch pleated filter is the number one cause of an assortment of HVAC and indoor air quality issues (to include cracked heat exchangers and failed air conditioning compressors).

It’s not just about the filter, it’s about the system design associated with the filter.

#1 the air filter is not designed to clean the indoor air of your house.

It is there to protect the evaporator coil from large particulate matter (such as dog and cat hair). Anything that passes through a cheap filter will also pass the evaporator due to its bypass factor.

The average design run time for HVAC equipment is not sufficient for the number of air changes per hour required to clean the indoor air through a standard HVAC filter. The filter is to protect the equipment, not to clean the air. There is specific equipment for cleaning the air and it’s not a 1 inch pleated filter.

#2 according to the Department of Energy, HVAC air duct leaks 30% (on a good day).

Changing to a 1 inch pleated filter increases the negative static pressure of the HVAC duct system significantly increasing the air duct leakage above the 30%.

A 1 inch pleated filter that causes increased air duct leakage makes the indoor air of your house dirtier rather than cleaner! Why do you have to clean your air ducts? Because they leak! Not because the filter does not collect the dirt. Increasing leakage downstream of the 1 inch pleated filter pulls in the dirty air from where the duct is located (attics, crawl spaces, inside of partition walls). The HVAC system distributes this dirt throughout the house and for the most part never makes it back to the 1 inch pleated filter to be filtered out (especially if the airflow has been restricted). Even if the filter works, you are exposed to the dirt and allergens on their way back to the filter. This contributes to significant indoor air quality issues.

Many return air duct designs do not meet the manufacturers static pressure requirements (even without a filter installed). Does anyone know what these specifications are? Does anyone carry the equipment required to conduct this test?

#3 a dirty filter is more efficient than a clean filter.

As a filter is used it becomes more efficient before becomes inefficient. The dust and dirt initially collected on the filter surface becomes part of the filter media and itself collects other dirt before it makes it to the filter surface.

This is similar to a swimming pool filter. If you have very fine suspended particulate matter in your swimming pool and you constantly back flush the sand filter it takes a longer time to clear the water (if it ever clears). As the sand in the filter becomes clogged, it collects finer and finer materials until water flow is restricted to a point that it must be removed. Just like the air filter.

A dirty filter does not consume more electricity!
Restricting airflow through the air duct system lowers the amperage draw on the fan. Look up the fan curve! It doesn’t make it harder for the fan to run, it makes it easier! There is less volume for the fan to move so it spins freely. For you fisherman; when your propeller cavitates (from excessive horsepower applied to the propeller versus the propellers design to move water) does the engine speed up or slow down? It speeds up because there is less load on the prop.

Mr. Jones, please explain to me how a standard HVAC filter provides you with “fresh air”?

When all of the situations above occur, you not only get dirt in the house but you get the contaminants (such as radon and mold spores) associated with the air duct location.

Anyway, these are the undisputed facts weather you wish to accept them or not…

Very interesting perspective, David. Your #3 answer is kinda like the K&N replacement filter for your vehicle. The dirtier it gets it gets better at filtering out the dirt and debris that can harm your engine. I think I’ll do a little digging around on the Internet to better understand HVAC filters. I alway knew that they are there to protect the equipment because that’s what I was taught in school.

Is there a consensus on what is the best filter for your HVAC. On the disposals the HVAC man says Plead no smaller than 1". So the filter is working at optimum when it is sucked into the fan or just before? Thanks John

In relation to cheap air filters you are with in time in changing it. I am using HEPA filters for my furnace and it has the capacity to catch 99.9% dust particles. If it is maintained properly it’s life expectancy can go more than 4 years.