How often do you change your furnace filters?

[jeromedawg]

Hey all,

Was curious how often furnace filters should be changed. If we don't run our AC or heater that often, should we still change it on a regular basis? Conversely, if I'm running the AC relatively frequently during the summer months (and furnace during winter months), how often would I want to change the filter?

[Orvell]

You can buy filters that last varying periods of time. The filters in the apartment I last rented were good for (3) months.

[Spork]

I do 3 months.   We run ours intermittently all year.  In the winter when we heat with a wood stove, we still use the HVAC to circulate the air.  (Fan only, no heat.)

[Vindicated]

Thanks for the push!  I keep forgetting to change mine, over 4 months now.  I've now set a reminder to do it tonight, and made it recurring every 4 months.

Oh, I try to aim for 4 months, because mine never seem that dirty, even after 4 months.

[ketchup]

I only change mine when I use my furnace (have window AC units for the summer).  We have dogs so probably a bit more dust and hair in the air than average, so in the winter I do about every month, maybe two months if I know we've used it less.  I don't buy the fancy filters.

[HipGnosis]

Thanks for the push!  I keep forgetting to change mine, over 4 months now.  I've now set a reminder to do it tonight, and made it recurring every 4 months.

Oh, I try to aim for 4 months, because mine never seem that dirty, even after 4 months.

This is the technically correct answer, which is: "when they're dirty".   
There are many factors that determine how often they get dirty;
Number of people in the house; living or visiting.   # of smokers, how much they smoke
Pets - #, size and dander / shed rates are all different
How well the house is or isn't insulated contributes to how often the furnace & central air run

I look at the recommended change time on the filter as a recommendation for a worse case scenario and then factor in that the mfg makes more money if they are changed more often.

[BlueMR2]

6 months, per the manual.  Looking at them at that period of time and comparing to the car air filter replacement pictures, I'd say it's just about right.

[lthenderson]

I bought a reusable one. I rinse it out about three or four times a year and stick the thing back in. I haven't bought a new filter in over five years since I lived here.

[bacchi]

I bought a reusable one. I rinse it out about three or four times a year and stick the thing back in. I haven't bought a new filter in over five years since I lived here.

Mine is a reusable, static, filter too. Use the spray nozzle on it, let it dry, and replace it. Easy and no waste.

[BudgetSlasher]

Our is supposed to be every six month (which is just about correct), in reality that turns into once a year when the system (fuel oil) is serviced before heating season starts. No AC here so the system sits mostly dormant for roughly half the year.

[sol]

Once per year at the beginning of the heating season, then once more about halfway through the winter, then it's off for six months so it just sits dirty.

But one of our renters didn't clean the electronic air cleaner filter for approximately four years.  The blower went out and then it overheated and fried the board, and it cost us several hundred dollars to fix.  If you have renters, I suggest you make furnace filter maintenance a requirement of the lease.

[jeromedawg]

Once per year at the beginning of the heating season, then once more about halfway through the winter, then it's off for six months so it just sits dirty.

But one of our renters didn't clean the electronic air cleaner filter for approximately four years.  The blower went out and then it overheated and fried the board, and it cost us several hundred dollars to fix.  If you have renters, I suggest you make furnace filter maintenance a requirement of the lease.

Very good checklist item for rentals! Definitely something I'll have to keep in mind as I eventually want to get into REI with buy and holds.

[Geneseo1911]

You guys will like this.... bought this manometer on amazon for around $25. One probe goes on either side of the filter. Measure pressure drop with a new filter. Change when pressure drop across filter becomes excessive.

A new 20x25x5 13 Merv filter produces about  .17" water restriction. Maximum for the whole furnace according to the manual is 1.25".  the heat exchanger and a coil are about .25", so I plan to change mine at .45" as I don't want the fan working too hard. After 1 year, the filter is at .18".

In my previous house that had 1" filters, they would go about a year before needing to be changed.

[CptCool]

I just go with the cheap <$1 fibergalss filters and change it every month on the first of the month. It costs ~$12/year and that way I don't forget & don't have to worry about burning up the motor which is way more expensive than filters.

FWIW I've heard bad things about the more expensive filters as they strain the system much more

[Spork]

I just go with the cheap <$1 fibergalss filters and change it every month on the first of the month. It costs ~$12/year and that way I don't forget & don't have to worry about burning up the motor which is way more expensive than filters.

FWIW I've heard bad things about the more expensive filters as they strain the system much more

While this is true... the more filtration you do, the harder it is to move air through it.... There is a trade off.  IMO the fiberglass filters really don't stop much at all.  You can go low to mid range on the pleated filters and stop a whole lot more.  For us, that means "less dusting".

http://www.mechreps.com/PDF/Merv_Rating_Chart.pdf

[Prairie Stash]

You guys will like this.... bought this manometer on amazon for around $25. One probe goes on either side of the filter. Measure pressure drop with a new filter. Change when pressure drop across filter becomes excessive.

A new 20x25x5 13 Merv filter produces about  .17" water restriction. Maximum for the whole furnace according to the manual is 1.25".  the heat exchanger and a coil are about .25", so I plan to change mine at .45" as I don't want the fan working too hard. After 1 year, the filter is at .18".

In my previous house that had 1" filters, they would go about a year before needing to be changed.

I'm installing a manometer this weekend, great idea. I have a couple manometers lying around without any use.

Next week I'll post this in the money saving tricks, it should cut down on how often I change my furnace filter,  or speed it up and extend my blower fans lifespan. 

[Lan Mandragoran]

Thats a idea Sol. With our rental we keep running into random stuff that just pops up out of seemingly nowhere (and the furnace would have been another one of those for :P).

[MasterStache]

I don't think there is a set time frame. We replace when dirty. I check on occasion. We also have 4 animals that contribute a lot of fur/dirt.