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1" Furnace filter interval changes

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  • Jun 19th, 2019 10:50 pm
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1" Furnace filter interval changes

It seems like 3M and various filter companies say to change the furnace filter every 3 months. However, looking at my furnace filter, it doesn't look that bad after 90 days.

What I find peculiar are statements like:

https://filterbuy.com/how-often-do-i-re ... ac-filter/

"As your filter traps more dirt, dust, and allergens from the air, filter efficiency decreases. Find out below if you should be replacing your filter more often. "

Well, no. As the filter traps more junk, the efficiency of the filter actually increases as it now can capture smaller particles than as designed.

So while the above is biased, how often should we be changing 1" furnace filters?
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Feb 11, 2007
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angryaudifanatic wrote: It seems like 3M and various filter companies say to change the furnace filter every 3 months. However, looking at my furnace filter, it doesn't look that bad after 90 days.

What I find peculiar are statements like:

https://filterbuy.com/how-often-do-i-re ... ac-filter/

"As your filter traps more dirt, dust, and allergens from the air, filter efficiency decreases. Find out below if you should be replacing your filter more often. "

Well, no. As the filter traps more junk, the efficiency of the filter actually increases as it now can capture smaller particles than as designed.

So while the above is biased, how often should we be changing 1" furnace filters?
It's the efficiency of airflow through the filter that falls, leading to reduced airflow and increased load on your blower motor.
You could try to extend your interval by vacuuming the filter and/or blowing it out. Not sure if worth the effort for the $5 1in filters I used to use. I now have a 5in filters and change around every 6 months with occasional cleanings.
Also depends on how much your run your fan. If you keep it on 24/7 it'll obviously clog sooner, and depends how dusty your house is, especially if you have pets.
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[OP]
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engineered wrote: It's the efficiency of airflow through the filter that falls, leading to reduced airflow and increased load on your blower motor.
You could try to extend your interval by vacuuming the filter and/or blowing it out. Not sure if worth the effort for the $5 1in filters I used to use. I now have a 5in filters and change around every 6 months with occasional cleanings.
Also depends on how much your run your fan. If you keep it on 24/7 it'll obviously clog sooner, and depends how dusty your house is, especially if you have pets.
I certainly defer to your expertise. Fan is on 24x7. It's just that when I hold it up to the light, it'd not even remotely close to brown/dark. That's why I am skeptical, but point is duly noted. You don't go by color at all?
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angryaudifanatic wrote: I certainly defer to your expertise. Fan is on 24x7. It's just that when I hold it up to the light, it'd not even remotely close to brown/dark. That's why I am skeptical, but point is duly noted. You don't go by color at all?
Your house may be very clean/dust free, in which it wouldn't clog the filter very quickly. You can compare it to a new one to see how dark it is to get an idea.
The only way to be sure would be to use an manometer to compare the pressure drop of a new filter and the used filter.
Another way is to check your temperature rise/drop when heating/cooling. If it heats the air too high, or cools it too low, that means not enough air is flowing over the burners/coils.



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Jul 30, 2007
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I changed mine out every heating season (really from Oct - Mar) with interim inspection of the filter at around early January to see how much dirt is on the filter.
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Buy cheaper Merv-8 filters and check monthly. If it's relatively clean, check again in 2wks and so on.... If it's dirty, replace.

You'll find that it will be dirtier and replaced as often as the increased frequency of use (i.e. heating season / cooling season)
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I got some cheap ones and replaced it every 6 weeks or so.
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I buy Merv-8' by the case from a wholesaler and change the furnace filter at my home and rentals every 3 months regardless ... cheap insurance.
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Where do you guys buy furnace filters?
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I like the feature on my ecobee thermostat that monitors the run time of the fan and gives you a notice when your filter hits a certain amount of hours. More accurate the time based (ex. Every month or whatever)
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adblink182 wrote: I like the feature on my ecobee thermostat that monitors the run time of the fan and gives you a notice when your filter hits a certain amount of hours. More accurate the time based (ex. Every month or whatever)
And how many hours of run time do you have it set at? This would vary for everyone, wouldn't it? Pets, no pets, smoker, non-smoker?
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chimaican wrote: And how many hours of run time do you have it set at? This would vary for everyone, wouldn't it? Pets, no pets, smoker, non-smoker?
100% it woukd. But you could dial it in, set it at 100 and check it. If it still looks good add another 100 hours. I'm still working on mine but I think I'm near the 200 mark.

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