How often to change filter?


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Old 02-22-24, 11:23 AM
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How often to change filter?

I have a 95% efficient furnace and I have been changing the filer every 5 or 6 weeks. I think that's too often.
In the photo is a new one and the existing one. I can clearly see light through the old one.
Does it look like it's dirty enough to change? I buy boxes of these but they are getting pretty pricey.

 
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Old 02-22-24, 12:11 PM
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Seeing light through an HVAC filter is a common way to determine when it's time to replace it. The issue, though, should not be if a filter is "dirty enough to change". Rather it should be is the filter too dirty to use. HVAC systems often have issues due to failing to replace the filter timely. A dirty air filter can restrict air flow into the air handler, hindering the flow of air and eventually wearing out the unit. When in doubt, it's time to replace the filter. It's far more cost effective to replace the air filter early versus taking a chance on damaging the air handler.

Having said that, perhaps replacing the filter every 5-6 weeks may be early. Typically, filters last 2 months or more. It could be, however, that your home or ducts are dustier than normal; perhaps you have pets. Also, your filter seems to be MERV 8 or higher filter. Higher rated filters will capture more contaminants which often requires more frequent replacement. I suspect having a lower MERV rated filter could be a good solution for you. Keep in mind that the filter is there to protect the HVAC system, not to purify the air and a MERV 8 or higher filter is unnecessary for that purpose.
 

Last edited by Tony P.; 02-22-24 at 12:41 PM.
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Old 02-22-24, 01:19 PM
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Thanks. I am definitely not the type who doesn't change them. I never understood the reasoning there. These are MERV 8 filters - you're right. I'll step them down a bit and see if they still need changing every 6 weeks or so.
 
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Old 02-22-24, 03:28 PM
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DenverGuy, IMO most HVAC contractors will tell you an HVAC filter looks like this:


I use a MERV 4 filter which has a bit more substance but for no other particular reason.
 
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Old 02-22-24, 06:16 PM
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Tony, thanks. For what it's worth mine isn't HVAC - only heat. But I'm going to order lower value MERV filters next time.
 
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Old 02-22-24, 06:29 PM
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The higher the number the better the filter.
 
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Old 02-23-24, 06:20 AM
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Pete, thanks for the chart. However, I'm not sure that a higher MERV value necessarily means that it's better. Too high and you're restricting airflow and causing the blower to work a lot harder.
 
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Old 02-23-24, 01:25 PM
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Pete, thanks for the chart. However, I'm not sure that a higher MERV value necessarily means that it's better. Too high and you're restricting airflow and causing the blower to work a lot harder.
DenverGuy, an air filter traps and holds particles and contaminants. A higher MERV value means implicitly that it can filter more than a lower MERV rated filter. Therefore, a higher MERV rated filter is inherently better than a lower rated filter.

But you correctly imply that the best filter isn't always the right filter. Cost, resistance, replacement frequency, and air quality are also factors.
 
 

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