Furnace noise question

Exterous

Super Moderator
Jun 20, 2006
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Happened to be in the basement when the furnace blower fired up so I noticed a higher pitched humming noise. I couldn't actually localize it but while I was trying to track it down I noticed it went away as I pulled the filter out. I'm guessing this is from the added strain of the filter on the blower and a sign that I should replace it? (It does settle down after a minute or two on its own. For now). You can kinda hear the noise around the 5 second mark:

 

PowerEngineer

Diamond Member
Oct 22, 2001
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I notice you got a fancy ass 3M Filtrete there.
This may or may not have an impact, but every HVAC guy I ever talked to said you should use cheap ass cardboard filters and replace them frequently. The fancy ones just clog up and slow the air flow.

Yes, I have had the same thing explained to me. Regardless of how new or clean they might be, filters with high MERV values confront your furnace fan with a higher resistance to air flow that it might be designed to handle. The results can be lower air flow through your HVAC system (and therefore poorer heating and cooling performance) as well as extra strain on the fan. If you want to have better indoor air quality, it may be better to put a stand-alone air purifier inside the house and just use the manufacturer's recommended filters.
 

Exterous

Super Moderator
Jun 20, 2006
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How long since you have replaced the filter?
I notice you got a fancy ass 3M Filtrete there.
This may or may not have an impact, but every HVAC guy I ever talked to said you should use cheap ass cardboard filters and replace them frequently. The fancy ones just clog up and slow the air flow.
1 month ago. I replace them every 2 months and don't go for the highest filtration. I know it's more strain but I do find allergy issue reduction with these over the cheap ones and that's worth only getting 10 years out of the blower if it's time to replace it
 

snoopy7548

Diamond Member
Jan 1, 2005
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Almost sounds like what happens when you blow on a piece of paper sideways, like an oscillation of the filter's cardboard when the air is blowing past it.
 

mindless1

Diamond Member
Aug 11, 2001
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If this is a new sound, wasn't there previously, with high filtration filters, then the blower motor is probably due to be lubed.

Used to be, blower motors had lube ports but not so much in recent decades so it can be a bit of a process, pulling motor, cleaning squirrel cage while it's out, taking end caps off the motor to replenish the oil reservoirs at both ends.

Some people would just buy a new one, but by the time you had to remove it and install *something* anyway, it's not much more work at that point to lube most motors, as long as the end caps aren't welded on.

If it's not ancient it probably has an inducer motor too, which may also be due to be lubed. I just use 5W-20 motor oil, main thing is relube before they get too loud which is a sign of the bushings/bearings progressively accelerating in wear from needing lubed.

At the same time, lack of lube and wear tends to make noise even without the extra load of the higher impedance filters... just suggesting that replacing the motor probably isn't necessary at this point.
 
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Red Squirrel

No Lifer
May 24, 2003
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www.anyf.ca
I notice you got a fancy ass 3M Filtrete there.
This may or may not have an impact, but every HVAC guy I ever talked to said you should use cheap ass cardboard filters and replace them frequently. The fancy ones just clog up and slow the air flow.

Yeah I did the same mistake with my furnace, got a fancy hepa filter and it was causing too much air restriction which ended up causing the blower to rattle a lot as it's not 100% balanced I guess. If you want to use the fancy filters you need to either drop the blower speed or find a way to maximize the surface area, and use 2 or more of them. Crossed my mind to cut a diagnal line right through the return trunk and make that the filter insert bay but I just opted to use the cheap filters and it's been good enough.
 

MrSquished

Lifer
Jan 14, 2013
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Good info here. I've been buying the 'higher end' filters for my HVAC but today I bought the base version. Under 5 bucks vs 15, still gets dust and pollen and pet dander. My HVAC is louder than I want, I'm hoping it is on for shorter periods if it's getting better airflow