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Old 11-30-2019, 01:21 AM   #16
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Re: AC filter question


just set the input unit correctly - cfm.

I'm getting 366 fpm with those dimensions which should be okay but not ideal.

just make sure it's changed frequently enough.
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Old 11-30-2019, 01:22 AM   #17
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Re: AC filter question


Pleated filters work well. As the filter gets dirty, it filters better because the holes where small particles get through get smaller. Of course as it gets dirty it is more restrictive. Optimally, the filter would be allowed to get dirty to the point of excessive restriction, then get changed. My gas and wood furnaces use the same filter. I frequently put a new filter in the gas furnace and put its old filter in the wood furnace. Then I am sure to change it on the expensive gas unit before it gets very dirty.
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Old 11-30-2019, 01:33 AM   #18
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Re: AC filter question


O.k. the consensus seems to be a pleated filters- 8 Merv is acceptable for a 3.5 ton AC unit.

But don't let renter use anything higher than 8 Merv and check to make sure the filter is changed on a regular basis.

Thank you.
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Old 11-30-2019, 06:32 AM   #19
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Re: AC filter question


While MERV 8 "should" be okay to use. Check the temp rise as you were advised earlier in the thread.

Put a new air filter of the type that you have been using in, then check temp rise. Record it. Then put a new MERV 8 pleated air filter in, and recheck temp rise and record it.

Check the allowable temp rise listed on the furnace/air handler label. If the MERV 8 filter is close to the max allowable, don't use it.
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Old 11-30-2019, 11:42 AM   #20
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Re: AC filter question


This thread has inspired me to check my own filter to see where I stand. I prefer the easy way, just checking the ∆ T across the heat exchanger.

The spec sheet for my Trane UD080C936J furnace shows a table for all Trane
units listing CFM VS. Temperature rise. The extreme values for my furnace are 59 @ 1000 crm and 42 @ 1400 cfm. Presumably operating outside of that range is not recommended. I ran a test using an old MERV 8 filter that I saved when I was making a futile attempt to reduce the dust in the house.

The results of my test indicated my heat exchanger had a ∆ T of 47. Switching back to my cheap fiberglass filter, I got a reading of 45. From that quick and easy test, I think the Trane furnaces have a conservative rating and could allow using even higher MERV filters above 8. My filter bay will only accommodate a 16x25x1 filter but apparently that's plenty big enough. My simple test ignores any other factors like return air duct size, increased frequency of required filter change, fan motor wattage and occupants sensitivity to drafts, etc. add infinitum...

YMMV, do your own testing if you feel the need. It's good exercise!
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Old 11-30-2019, 11:53 AM   #21
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Re: AC filter question


Across the open rectangle space where the filter sits I have suspended a taut vertical wire, to give more support to cheap filter, in the middle, to keep from bending.

I use painter's blue tape around all 4 sides to seal in place.

I write the replacement date on the blue tape.

When vacuuming air handler must be off.
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Old 11-30-2019, 12:19 PM   #22
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Re: AC filter question


Quote:
Originally Posted by surferdude2 View Post
This thread has inspired me to check my own filter to see where I stand. I prefer the easy way, just checking the ∆ T across the heat exchanger.

The spec sheet for my Trane UD080C936J furnace shows a table for all Trane
units listing CFM VS. Temperature rise. The extreme values for my furnace are 59 @ 1000 crm and 42 @ 1400 cfm. Presumably operating outside of that range is not recommended. I ran a test using an old MERV 8 filter that I saved when I was making a futile attempt to reduce the dust in the house.

The results of my test indicated my heat exchanger had a ∆ T of 47. Switching back to my cheap fiberglass filter, I got a reading of 45. From that quick and easy test, I think the Trane furnaces have a conservative rating and could allow using even higher MERV filters above 8. My filter bay will only accommodate a 16x25x1 filter but apparently that's plenty big enough. My simple test ignores any other factors like return air duct size, increased frequency of required filter change, fan motor wattage and occupants sensitivity to drafts, etc. add infinitum...

YMMV, do your own testing if you feel the need. It's good exercise!
Thanks again everyone for your input and suggestions.

My rental is 1490 sq ft and uses 3.5 ton package unit and filter size is 20x30x1

I always provide my renters with free ac filters (cheap fiberglass) to ensure they change them monthly.

And I check every two months to make sure a new one is in place.

Unfortunately, I occasionally get renters who complain cheap filters recycle dust or pollen is an issue.

I can have my AC guy come over and run a test. This way he could speak with the renter and point out why or why not an 8 Merv filter should or shouldn't be used.

The last time this happened a renter got upset and didn't want to use the cheap filters. However, but it didn't matter because he was in the process of moving anyway.

With renters I need to pick my battles esp if this (type of air filter) is the only sticking point.

The current renter complained the cheap filter didn't prevent enough dust from escaping. So, he went out and bought the Rheem 8 merv filters. I found this out when I went by to inspect if a new filter was in place.

If I understand correctly the 20x30x1 Rheem 8 Merv filter should be fine with a 3.5 ton unit (1490 sq ft home.) And as long as it is regularly replaced any restriction in air flow is minor.

Or... am I mistaken? That I should have my AC vendor to come over and check?

It's not a question of the $45 I will spend for my AC guy to come out.

But a question of whether this (cheap filter vs. 8 merv filter) is worth pushing the tenant over. Given the specs I have provided above appear to suggest any air flow restriction will be minor.

Last edited by ken33xx; 11-30-2019 at 12:28 PM.
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Old 11-30-2019, 12:42 PM   #23
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Re: AC filter question


Install a washable hog hair electrostatic and the whining tenants can see what's being filtered out.Vacuum, wash by back flushing and hang to dry. This old blower was pulled a week ago for a lube job and after 36 years of operating temperatures from +113F to -21F it still doesn't need cleaning. What's that old saying? The proof is in the pudding.
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Old 11-30-2019, 12:56 PM   #24
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Re: AC filter question


I think it would be worth the service call to get the temperature rise measured by a pro. Then you will have better credibility and possibly be above reproach from your renter.

Even so, the old adage states, "A man convinced against his will, is of the same mind still."
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Last edited by surferdude2; 11-30-2019 at 01:01 PM.
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Old 11-30-2019, 01:37 PM   #25
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Re: AC filter question


a really good pro would check static pressure in addition to air temps, it's a more reliable test than temp drop/rise alone.

reducing airflow can change capacity a little and for cooling, reduce it as well and shift from actual cooling to dehumidification.
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Old 11-30-2019, 02:34 PM   #26
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Re: AC filter question


O.k I texted the AC vendor I have been using for installs and maintenance. He's got some 40 years experience in the field.

He told me the Rheem 8 merv for a 1490 sq ft home 3.5 ton AC with filter size 20x30x1 isn't a problem.

However, it is important the filter be changed once a month during the summer. (Property is in AZ.)

6-8 weeks is acceptable during the winter months.
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Old 11-30-2019, 04:01 PM   #27
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Re: AC filter question


Quote:
Originally Posted by surferdude2 View Post
Even so, the old adage states, "A man convinced against his will, is of the same mind still."
How true that is.
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Old 12-01-2019, 06:52 AM   #28
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Re: AC filter question


Quote:
Originally Posted by ken33xx View Post
O.k I texted the AC vendor I have been using for installs and maintenance. He's got some 40 years experience in the field.

He told me the Rheem 8 merv for a 1490 sq ft home 3.5 ton AC with filter size 20x30x1 isn't a problem.

However, it is important the filter be changed once a month during the summer. (Property is in AZ.)

6-8 weeks is acceptable during the winter months.
Check to see how much it has bowled inward after 30 days of use in the summer.
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Old 12-01-2019, 10:54 AM   #29
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Re: AC filter question


Yes benthere, that's the best way to convince customers that they need to change their filter a little more frequently. Add to that with a little info about what a blower motor costs and why the furnace will be fubar if the heat exchanger gets damaged. I've had customers ask me why they didn't make stronger filter, so they wouldn't cave in like that.
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Old 12-01-2019, 11:03 AM   #30
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Re: AC filter question


On some industrial engines the air filter has a pop out indicator when the filter needs to be replaced. I suppose this is due to pressure differential. Is this type of indicator available for residential HVAC applications?
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