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When to Change my 4 Inch Furnace Filter? #4665733
02/14/18 11:41 AM
02/14/18 11:41 AM
Joined: Sep 2002
Posts: 2,385
VA
Gebo Offline OP
Gebo  Offline OP
Joined: Sep 2002
Posts: 2,385
VA
I just installed one of those 5 inch furnace filters. I attached one of those vacuum differential devices as well. When furnace blower runs in propane mode is shows .20 inches of water. When furnace runs in HP mode is shows .30 inches of water. Reason being the fan runs slower in the Propane mode.

My question is how high does the resistance need to go before I replace the filter?




'98 LEX LS400 280K
'00 LEX GS300 195K
'02 4Runner 225K
'05 Lex LS430 85K
'06 Toyota Highlander 145K
'09 Lex IS350 85K
'07 Lex GX470 60K
Amsoil in all engines, transmissions and differentials

Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4665743
02/14/18 11:48 AM
02/14/18 11:48 AM
Joined: Dec 2009
Posts: 762
Battle Creek, MI
SVTCobra Offline
SVTCobra  Offline
Joined: Dec 2009
Posts: 762
Battle Creek, MI
First thing I would do is make sure the Magnehelic is level and vertical, otherwise the readings won't be accurate.

Can't help answering your question though.


Think twice, speak once.
Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4665758
02/14/18 12:04 PM
02/14/18 12:04 PM
Joined: Jul 2014
Posts: 132
North TEXAS
oldoak2000 Online content
oldoak2000  Online Content
Joined: Jul 2014
Posts: 132
North TEXAS
Originally Posted By: Gebo
I just installed one of those 5 inch furnace filters. I attached one of those vacuum differential devices as well. When furnace blower runs in propane mode is shows .20 inches of water. When furnace runs in HP mode is shows .30 inches of water. Reason being the fan runs slower in the Propane mode.
My question is how high does the resistance need to go before I replace the filter?
..


Interesting, I woulda thought the CFM should be higher for the propane furnace?
how many btu is the furnace, and how many btu is the heatpump ??

If you have the heatpump model, there should be a chart on in the specs that show performace at specific cfm's (your ultimate answer can be calculated from that).
However, IF you have ECM/variable blower motor, it can automatically compensate for filter loading to maintain ideal performance (assuming a perfect/near-perfect install).

5" media filters are the LEAST likely to get 'loaded up' prior to the 6-month swap time; too much older than that you'll get mite population munching the dead skin cells buildup (dust) right ON the filter (releasing THEIR allergens into the flow) frown

Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4665844
02/14/18 01:31 PM
02/14/18 01:31 PM
Joined: Feb 2013
Posts: 11,102
Phoenix, AZ
Nick1994 Offline
Nick1994  Offline
Joined: Feb 2013
Posts: 11,102
Phoenix, AZ
Slip a new one in and see what the pressures are for a new filter. If it's the same or close and it looks ok put the old one back in.


2015 Hyundai Sonata 2.4L 89k Motorcraft Synthetic Blend 5w30 & OEM
2000 Toyota Camry 2.2L 231k Valvoline 5w30 & Fram Ultra
1996 Jeep Cherokee 4.0L 147k Mobil 1 HM 10w40 & Fram Ultra
Re: When to Change my 4 Inch Furnace Filter? [Re: Nick1994] #4665873
02/14/18 01:55 PM
02/14/18 01:55 PM
Joined: Sep 2002
Posts: 2,385
VA
Gebo Offline OP
Gebo  Offline OP
Joined: Sep 2002
Posts: 2,385
VA
Originally Posted By: Nick1994
Slip a new one in and see what the pressures are for a new filter. If it's the same or close and it looks ok put the old one back in.


The above readings are with the new filter. I was wondering if we had some super-duper HVAC genius's here on BITOG. I'm sure we do.

IF .2 and .3 are my starting points, at what pressure differential is my filter getting too restrictive?


'98 LEX LS400 280K
'00 LEX GS300 195K
'02 4Runner 225K
'05 Lex LS430 85K
'06 Toyota Highlander 145K
'09 Lex IS350 85K
'07 Lex GX470 60K
Amsoil in all engines, transmissions and differentials

Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4665920
02/14/18 02:44 PM
02/14/18 02:44 PM
Joined: Dec 2002
Posts: 861
Stillwater, MN
road_rascal Offline
road_rascal  Offline
Joined: Dec 2002
Posts: 861
Stillwater, MN
The old house we owned before we moved had a 20x20x5 Air Boss filter. I changed it every 6 months. This was based on several HVAC people I know.


2012 Toyota Rav4 V6 4WD (73,000 mi)
2018 Chevy Equinox 1.5T (7800mi)
Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4665970
02/14/18 03:37 PM
02/14/18 03:37 PM
Joined: May 2014
Posts: 3,835
Columbus,Nebraska
Yah-Tah-Hey Offline
Yah-Tah-Hey  Offline
Joined: May 2014
Posts: 3,835
Columbus,Nebraska
Ask Lennox

Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4666104
02/14/18 06:11 PM
02/14/18 06:11 PM
Joined: Aug 2003
Posts: 13,147
NE,Ohio
Rand Offline
Rand  Offline
Joined: Aug 2003
Posts: 13,147
NE,Ohio
usually 2x a year

unless it runs a ton a few extra months esp the spring or fall when it wont run as much wont hurt.

ie if you are feeling cheap you can stretch it to 8months easy enough but maybe not 1 year.

And the highest usage months are summer and winter usually in our climate.


2019 Jeep Cherokee Trailhawk 2.0T
Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4666120
02/14/18 06:35 PM
02/14/18 06:35 PM
Joined: Sep 2017
Posts: 315
One Step Beyond
MasterSolenoid Offline
MasterSolenoid  Offline
Joined: Sep 2017
Posts: 315
One Step Beyond
Same gage I installed on my furnace.
I'm only a home owner, not a contractor.
This is just my 2 cents.

You want to find the maximum static pressure of your furnace.
Don't make the mistake of guessing.
The info should be on a label inside your furnace.
If you can not find it, call the manufacturer.

My furnace is max static pressure of .50" of water column.
My filters are one inch thick.
New filter reading .32"
After one year ... reading of .44
So, I could go longer, but change at one year.

Like other poster said, mount the gage as it was designed to be.



I also noticed, when the fan runs higher RPM, the gage will give a higher reading.
I only have natural gas, but my furnace fan is two speeds.
My fan only goes to higher RPM after 10 minutes of running. Which is hardly ever.



Last edited by MasterSolenoid; 02/14/18 06:42 PM.

2002 Ford Ranger
2 Wheel Drive
3.0 Liter Engine
- - - - - - - - - - - - - -
Four basic premises of writing:
Clarity, Brevity, Simplicity, and Humanity.
Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4666173
02/14/18 07:45 PM
02/14/18 07:45 PM
Joined: Jan 2013
Posts: 1,676
Wisconsin
WiskyBadger Offline
WiskyBadger  Offline
Joined: Jan 2013
Posts: 1,676
Wisconsin
I change mine at a year, based on a couple hvac fellas.


14 Buick Verano �Blanche� 61k Castrol Edge & Delco filter
01 Ford Ranger �Rick� 166k Castrol Magnatec Motorcraft
78 Chevy Stepside
11 Chevy Traverse 114k Carquest 5w30 and Carquest filter
Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4666195
02/14/18 08:02 PM
02/14/18 08:02 PM
Joined: Jul 2014
Posts: 557
Wisconsin
Srt20 Offline
Srt20  Offline
Joined: Jul 2014
Posts: 557
Wisconsin
I forgot about mine this fall. It had been in about a year, maybe a little less. It was so plugged, it burned up my fan motor. $150, and it was an easy replacement, but filters are alot cheaper and alot easier to replace.

Re: When to Change my 4 Inch Furnace Filter? [Re: Srt20] #4666240
02/14/18 08:42 PM
02/14/18 08:42 PM
Joined: Sep 2017
Posts: 315
One Step Beyond
MasterSolenoid Offline
MasterSolenoid  Offline
Joined: Sep 2017
Posts: 315
One Step Beyond
Originally Posted By: Srt20
I forgot about mine this fall. It had been in about a year, maybe a little less. It was so plugged, it burned up my fan motor. $150, and it was an easy replacement, but filters are alot cheaper and alot easier to replace.

I wonder what the static pressure was ?
That would be the difference in pressure before and after the filter.
Every Home and Furnace is different, that's why the filter Co. says to change every 3 Months.

But I like using the differential pressure gages.
I change it a little sooner than need be, but also know that I'm not changing them too soon or too late.

Another good thing with using the pressure gage is: there are cheap filters (spun glass) and there are
the best filter (HEPA) and several (pleated) in between.

Depending on the furnace and duct work, some people may use a (new) HEPA filter and be close to the maximum static pressure.
Then you have to use the next least restrictive filter.

Just my 2 cents.
I'm not a Contractor.


2002 Ford Ranger
2 Wheel Drive
3.0 Liter Engine
- - - - - - - - - - - - - -
Four basic premises of writing:
Clarity, Brevity, Simplicity, and Humanity.
Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4666291
02/14/18 09:46 PM
02/14/18 09:46 PM
Joined: Sep 2002
Posts: 2,385
VA
Gebo Offline OP
Gebo  Offline OP
Joined: Sep 2002
Posts: 2,385
VA
Mastersolenoid, thank you! I found the info on a tag in my furnace. .50 inches water pressure maximum. Thank you for your help! Most excellent.


'98 LEX LS400 280K
'00 LEX GS300 195K
'02 4Runner 225K
'05 Lex LS430 85K
'06 Toyota Highlander 145K
'09 Lex IS350 85K
'07 Lex GX470 60K
Amsoil in all engines, transmissions and differentials

Re: When to Change my 4 Inch Furnace Filter? [Re: MasterSolenoid] #4666303
02/14/18 09:54 PM
02/14/18 09:54 PM
Joined: Jul 2014
Posts: 557
Wisconsin
Srt20 Offline
Srt20  Offline
Joined: Jul 2014
Posts: 557
Wisconsin
Originally Posted By: MasterSolenoid
Originally Posted By: Srt20
I forgot about mine this fall. It had been in about a year, maybe a little less. It was so plugged, it burned up my fan motor. $150, and it was an easy replacement, but filters are alot cheaper and alot easier to replace.

I wonder what the static pressure was ?
That would be the difference in pressure before and after the filter.
Every Home and Furnace is different, that's why the filter Co. says to change every 3 Months.

But I like using the differential pressure gages.
I change it a little sooner than need be, but also know that I'm not changing them too soon or too late.

Another good thing with using the pressure gage is: there are cheap filters (spun glass) and there are
the best filter (HEPA) and several (pleated) in between.

Depending on the furnace and duct work, some people may use a (new) HEPA filter and be close to the maximum static pressure.
Then you have to use the next least restrictive filter.

Just my 2 cents.
I'm not a Contractor.






































IDK I dont have gauges, but it was enough to fold the filter over. The blower motor had to be working hard.

Re: When to Change my 4 Inch Furnace Filter? [Re: Gebo] #4666459
02/15/18 06:55 AM
02/15/18 06:55 AM
Joined: May 2007
Posts: 7,636
Indianapolis, IN
dnewton3 Offline
dnewton3  Offline
Joined: May 2007
Posts: 7,636
Indianapolis, IN
Typical filter dP should be no more than a few tenths of water column from baseline.
Example, if a "new" filter offers WC of .3", then by the time it gets to .6", it's time to change.


Anyone with minimal skills can build their own manometer at home. Just get some clear flexible plastic tubing, create a "U" shape, fill part-way with water, hang it vertically on a piece of cardboard and measure off inches above/below a baseline at atmospheric pressure. Put a couple of small port holes in the duct upstream and downstream of the filter; connect tubes. Viloa!


Last edited by dnewton3; 02/15/18 06:58 AM.

The act of preventative maintenance, in and of itself, is FAR MORE important than brand/grade/base choices among lubes and filters.
- under maintaining something is akin to abuse/neglect; that can kill equipment by shortening the lifespan
- over maintaining something has never been proven to be anything but a waste of time and money

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