Filters at return air grills being sucked into duct

[pimy]

Hello,

New member here. Thanks for taking the time to read this.

I have two return air grills, each approximately 14x30. I began to use pleated air filters with a high Merv rating (10 or 12 I think) because I was concerned with air quality in my home. I began to notice that when the air came on, the filters would be pulled out of place, and nearly sucked into the duct because of the air pressure. I searched for grills that could trap my filters but didn't find any at the local home improvement stores. Instead, I set up some velcro around the rim of the grill. I would then attach velcro to each new filter as I installed them. This kept the filters in place. I then spoke with someone with several years of A/C experience, and he explained I shouldn't be using such a restrictive filter. He said that plain, cheap, fiberglass filters are "nearly" as good at trapping air born pollutants. Additionally, they restrict a lot less air flow and are better for your a/c unit.

I finally honored his advice and custom ordered a box of 12 fiberglass filters. Installed them, A/c came on, and up went the filters. Seems that the pressure is so high that its even pulling these less restrictive filters. Is that much air pressure normal? Should I go back to searching for a grill that can trap the filter in place? Should I stay with the cheap filters, as long as I change them out monthly?

Also, one of the returns is just outside the master bedroom. Anytime that the unit comes on and the door is only partially open, the pressure will slam the door shut. A/c guy (see above) recommended that I wedge something in the door to help the air escape more easily, and thus improve the effeciency of the unit. Thoughts?

Thanks,
Rob

[makinmoney]

Not much info to go on, like Manufacturer, model# of Cond, AHU.....but it sounds like your returns are undersized, but if they are as bad as you say I can't see how your system would be running correctly.

The more info for us the better.........

[makinmoney]

Also, one of the returns is just outside the master bedroom. Anytime that the unit comes on and the door is only partially open, the pressure will slam the door shut. A/c guy (see above) recommended that I wedge something in the door to help the air escape more easily, and thus improve the effeciency of the unit. Thoughts?

Yeah....That's the dumbest thing I've ever heard. I'm alot dumber now that I heard that.

[4jime]

See if you can get someone to add another filter grill to the system, or in large the ones that are there.

[mark beiser]

Yeah....That's the dumbest thing I've ever heard. I'm alot dumber now that I heard that.

Actually it isn't dumb at all. The problem he describes is typical of a room that has a presurization problem due to not having enough/any return air, or a return path for air to get out of the room.

Wedging the door open is the best "free" fix for the problem...

[makinmoney]

Actually it isn't dumb at all. The problem he describes is typical of a room that has a presurization problem due to not having enough/any return air, or a return path for air to get out of the room.

Wedging the door open is the best "free" fix for the problem...

I respectfully disagree...The HO shouldn't have to manipulate his house to get the system running correctly. That's the same as you taking your car in for service and the mechanic saying " It was only running on 7 cylinders......so, we disconnected one more, now it's a V6......That'll be $300.00.

[mark beiser]

I respectfully disagree...The HO shouldn't have to manipulate his house to get the system running correctly. That's the same as you taking your car in for service and the mechanic saying " It was only running on 7 cylinders......so, we disconnected one more, now it's a V6......That'll be $300.00.

Like I said, it is the best "free" fix for the problem. Other more correct solutions will cost money. A good part of my business is correcting pressurization issues in homes. If someone doesn't want to pay, or can't afford to pay for the real solution to the problem, blocking doors open is their only real option.

Your engine analogy is a bit over the top...

[makinmoney]

[QUOTE=mark beiser;1554108]Like I said, it is the best "free" fix for the problem./QUOTE]

What got fixed...........the door slamming? It sure wasn't the system! I guess anytime he wants to have some alone time with the wife, ALL he has to do is go to the stat and put the fan in manual? That way the kids wont be able to open it due to the Vacuum being created..

[mark beiser]

I never said it was a good fix, there are no better "free" fixes for room pressurization issues though....

Duno why you are getting bent out of shape about it anyway, lol.

[k-fridge]

I respectfully disagree...The HO shouldn't have to manipulate his house to get the system running correctly. That's the same as you taking your car in for service and the mechanic saying " It was only running on 7 cylinders......so, we disconnected one more, now it's a V6......That'll be $300.00.
You're correct, but until the problem is remedied he can help by leaving the door ajar. That's all he's saying.

[makinmoney]

I never said it was a good fix, there are no better "free" fixes for room pressurization issues though....

Duno why you are getting bent out of shape about it anyway, lol.

I'm not getting mad.......my thing is that he was told to wedge the door and problem solved......There is a major problem in that house. From what we read you and I both know it.

[k-fridge]

To the original question....

Not much to go on but it seems like you may be short on return. You need to get a good HVAC man out to assess the situation and possibly add more returns...including one in your mater bedroom.

Don't use the high MERV filters in the 1" size, they are way too restrictive. The cheapo fiberglass filters on the other hand flow well but are often quite flimsy. For 1" filters my choice is the economy pleats.

[mark beiser]

I'm not getting mad.......my thing is that he was told to wedge the door and problem solved......There is a major problem in that house. From what we read you and I both know it.

I have the same problem in my own house, just bought it in March, won't be reducting the house until next year.
I have all my interior doors blocked open at the moment. ;)

I also have one of those Rheem/Ruud furnaces with the "3 ton" blowers that are notorious for being weak. I'm running it with no filter to improve airflow until I replace it next year. :rolleyes:

Between my 2 "free" fixes, I have dramatically improved the cooling performance of my system until I get a chance to fix it for real. :D

[pimy]

Not much info to go on, like Manufacturer, model# of Cond, AHU.....but it sounds like your returns are undersized, but if they are as bad as you say I can't see how your system would be running correctly.

The more info for us the better.........

Thank you all for the quick replies.

A/C Unit
Manu: Carrier
Model #: 38BRC042300
8.38 Lbs.
Power Supply: 208-230 Volts
62 Hz

Compressor: P. suppy 208/230 Volts A/C
Fan Motor: 1/4 HP
Test Pressure Gage: HI 300 PSI, LO 150 PSI

AHU
Manu: Carrier
Model #: ??
Efficiency: 80.0 AFUE
Type: 58 RAV downflow/horizontal induced-combustion furnace
I found the manual beneath the unit, and it is applicable to various models, each with a different size (E.g 050-08, 050-12, etc.). I can go back into my suana, err attic and measure the unit if you need that info.

Let me know if you need other information that I didn't provide.

Thanks again,
Rob

[pimy]

I'm not getting mad.......my thing is that he was told to wedge the door and problem solved......There is a major problem in that house. From what we read you and I both know it.

Hi,

I didn't mean to incite an argument. Mark is correct in that my A/C guy provided the advice from the perspective that it is a free fix. Keep in mind that he did recommend that I contact a local A/C guy to have the system assessed...but only if I planned to remain in this house for more than a short while. Sorry for not mentioning that sooner. Btw, imo you both have valid points.

Thanks,
Rob

[James Tramel]

Actually it isn't dumb at all. The problem he describes is typical of a room that has a presurization problem due to not having enough/any return air, or a return path for air to get out of the room.

Wedging the door open is the best "free" fix for the problem...

:) :)
Yuor absolutly right...the other fix to the prob cold be get smaller doors w at least a 1"-2" gap at the bottom so it will have ample return!!!!

[James Tramel]

I respectfully disagree...The HO shouldn't have to manipulate his house to get the system running correctly. That's the same as you taking your car in for service and the mechanic saying " It was only running on 7 cylinders......so, we disconnected one more, now it's a V6......That'll be $300.00.

I disagree with your disagreement......If there isnt enough gap at the bottom of the door then you'll have other prob too....Sometimes a unit can b sized rite but the home was poorly laid out....thus the home owners best choice would b to manipulate his home so he can get the correct return needed:D

[AcDOCnTRAINING]

Well there is some info missing like M/N#of furnace but I guess if you have a 3.5 ton condenser you probably have a 4ton blower which is about 1400-1500 CFM. If you take that @ .1 static pressure 2-14x30 returns should be plenty. However what is the diameter of the flex attached or size of the duct behind the return vent? Also, have you checked your evap. coil? A dirty coil will cause that fan to speed up a bit. How old is this unit?

[pimy]

Well there is some info missing like M/N#of furnace but I guess if you have a 3.5 ton condenser you probably have a 4ton blower which is about 1400-1500 CFM. If you take that @ .1 static pressure 2-14x30 returns should be plenty. However what is the diameter of the flex attached or size of the duct behind the return vent? Also, have you checked your evap. coil? A dirty coil will cause that fan to speed up a bit. How old is this unit?

I believe the unit was installed when the house was built. That would make it 10 years old. I'll check the unit again to see if there is a manufactured date on it. I know very little about how these things work...many of the the terms you used are quite foreign to me, but I'm learning as I go. :)

Duct #1 (near master - slamming door)
Diameter (min): 13
Diameter (max): 14

Duct #2 (near other bedrooms), more oval than circular
Diameter (min): 14
Diameter (max): 17

I'll try to find the M/n for the furnance later tonight or tomorrow. Are they typically located on the underside? Backside?

As for the evap coil, don't know anything about that...I need to do some research first. I can tell you that I haven't had it cleaned since I've lived here (3.5 years).

Thanks,
Rob

[pimy]

:) :)
Yuor absolutly right...the other fix to the prob cold be get smaller doors w at least a 1"-2" gap at the bottom so it will have ample return!!!!

I don't know if you were kidding...so I measured. There's approximately 1 inch clearance under the master doorway (double doors btw). That seems consistent with the other doorways in my home.

Cheers,
Rob

[skippedover]

:) :)
Yuor absolutly right...the other fix to the prob cold be get smaller doors w at least a 1"-2" gap at the bottom so it will have ample return!!!!

Want to know exactly how much to undercut a door in that situatuion? It's easy. From an open position, start closing the door. When you hit the point of equalibrium, that is, the door is just beginning to close on its own, stop the door movement and measure the distance between the door and the door jam, horizontally. Then just take that distance, multiply it by the height of the door, add in a little for the top & bottom (you can measure the trianglular distance and calculate it if you're being that specifici) then divide the total by the door width. The answer is the distance you need to under cut the door to maintain equilibrium. Most people don't want their doors cut up that far as it negates the purpose of having a door in the first place. For example, if the point of equilibrium is 4-inches, the door is 6' 6", that's 312 sq. inches of space needed. If the door is 30-inches wide, that's another 120 inches for the top & bottom together, giving a total open area of 432 sq. inches. Divide that by the 30-inch door width and you find you need to undercut the door 14.4 inches. Now THAT's an undercut!! :eek: :eek:

[James Tramel]

I don't know if you were kidding...so I measured. There's approximately 1 inch clearance under the master doorway (double doors btw). That seems consistent with the other doorways in my home.

Cheers,
Rob

I assure u i wasnt kidding..I was taught that by a guy who was in the industry 4 30+ yrs .....Im curious on what the prob is myself:)

[James Tramel]

Want to know exactly how much to undercut a door in that situatuion? It's easy. From an open position, start closing the door. When you hit the point of equalibrium, that is, the door is just beginning to close on its own, stop the door movement and measure the distance between the door and the door jam, horizontally. Then just take that distance, multiply it by the height of the door, add in a little for the top & bottom (you can measure the trianglular distance and calculate it if you're being that specifici) then divide the total by the door width. The answer is the distance you need to under cut the door to maintain equilibrium. Most people don't want their doors cut up that far as it negates the purpose of having a door in the first place. For example, if the point of equilibrium is 4-inches, the door is 6' 6", that's 312 sq. inches of space needed. If the door is 30-inches wide, that's another 120 inches for the top & bottom together, giving a total open area of 432 sq. inches. Divide that by the 30-inch door width and you find you need to undercut the door 14.4 inches. Now THAT's an undercut!! :eek: :eek:

Another possibility is return grills on the doors to the rooms it beets having the door 14in off the ground

[skippedover]

I disagree with your disagreement......If there isnt enough gap at the bottom of the door then you'll have other prob too....Sometimes a unit can b sized rite but the home was poorly laid out....thus the home owners best choice would b to manipulate his home so he can get the correct return needed:D

Okay, so let's consider that the man's home has 10 supply outlets, each sized to pump out 100 CFM. That's 1,000 CFM from the supply outlets. Now let's also assume that all doors to all rooms are open. The return is sized to allow 1,300 CFM of airflow. Now the unit kicks on. How much air flows through the system?

Well, if the system is perfectly tight, then 1,000 CFM, right? That's the maximum amount the supplies are designed to flow. But what if the system has a return leak from the attic? What if it leaks 15% of the total airflow? Now you're sucking in 1,000 CFM from the occupied space but 1,150 CFM total, with 150 CFM coming from the attic. The house is now under a positive pressure with air leaking out anywhere it can. Likewise if the supply duct leaks. If the return is tight, you end up pulling in more air than the supplies are delivering. Now the home is under negative pressure. Does that make doors slam closed? I guarantee it does. If you've ever done or seen a blower door test, try leaving a window open in one of the bedrooms when you start the blower motor. It will slam shut from wide open! Negative pressure is very motivating to doors on hinges!! :eek:

[pimy]

Another possibility is return grills on the doors to the rooms it beets having the door 14in off the ground

To be honest, I'm not bothered by the door slamming. My main concern is the issue of the filters being sucked up into the duct. This occurs at both returns whether or not the doors to the master are open. This might suggest that I need an additional return (k_fridge) or to enlarge existing returns, the fan is running too quickly (AcDOCnTRAINIG), or possibly a few other things. I still need to post furnance model # and inspect evap coil. Thanks.

[pimy]

Well there is some info missing like M/N#of furnace but I guess if you have a 3.5 ton condenser you probably have a 4ton blower which is about 1400-1500 CFM. If you take that @ .1 static pressure 2-14x30 returns should be plenty. However what is the diameter of the flex attached or size of the duct behind the return vent? Also, have you checked your evap. coil? A dirty coil will cause that fan to speed up a bit. How old is this unit?

I double-checked the manual, and then climbed into the attic for some measurements. The model appears to be 58RAV Series 161. I checked the site rules, and I didn't see anything about posting external links, hope it is allowed. Here is a link to the manual:

http://xpedio.carrier.com/idc/groups/public/documents/techlit/58ra-15si.pdf?SMSESSION=NO

I measured section A (see Fig. 1 in manual) and it is 17.5, which according to Table 1, narrows it down to a unit size of 095-12, 095-16, or 115-16. No way for me to gauge the weight. Maybe I have to remove some panels to get more info. I'm trying to avoid that unless absolutely necessary. Please let me know if more info is still needed. Thanks.

[dash]

To be honest, I'm not bothered by the door slamming. My main concern is the issue of the filters being sucked up into the duct. This occurs at both returns whether or not the doors to the master are open. This might suggest that I need an additional return (k_fridge) or to enlarge existing returns, the fan is running too quickly (AcDOCnTRAINIG), or possibly a few other things. I still need to post furnance model # and inspect evap coil. Thanks.

A 1' gap,single door,about 100 cfms,so the master likely has way more then 200 cfms ,so the door slams,and pressurizes the room,forces conditioned air to the outside,and sucks outside air into the rest of the home.Correct it,wedge the door ,jumper return,etc.,etc..

30" wide filter with no support,and high return static,slide several pieces of
14" coat hanger thru the filter to strengthen it,Until you can afford a Pro to test the the duct static,use the cheap filters,not the 1" pleated.

Do your returns have any frame to hold the filter,do the swing open to replace the filter/

[contactor]

Your doors are fine. You may have undersized duct connectors from return to furnace. Adding a return or two would help as well if you like those non alergen filters.

[Door guy]

First time poster so take it easy on me. What I have is a new york ait handler 3 ton installed in bonus room/ attic room 1100 sg. ft. Its been installed with return end on top with just the filter on top in a closet with just what i would call common returns into the closet or utility room the unit sits in. I know it might some what over sized and the blower runs i think the installer said on the highest speed so to get enough cfm for the 3 ton unit not to freeze up. The thing I am some what concerned with is when i turn this thing on it wants to really suck this filter in I just install a economy pleeted filter and wow it really sucks in. The filter is about the same size as the top of the air handler 20 x 20 the first thing I thought is maybe it should have a plenum and some how make it house a bigger or even 2 filters its like maybe its just to muck cfm thru this size filter ???? maybe nothen to worry about it does work and if it was to where i couldn't see the filter while running i would never know Just like to hear everyones input Thanks and what a great site

[markwolf]

If you want better filtration ditch the idea of a 1" filter alltogether.
Have a pleated filter like a spaceguard 2200 or carrier ez-flex installed at the furnace.If there are any duct leaks now or later this will not let dirt pass through the ducts & right back into the house & equipment.
It sucks to pay a guy like me by the hour to clean gobs of insulation out of a stopped up unit because you accidentally popped a duct apart when working in the attic & didn't notice until it was to late!
I do not care for undercutting doors or grills in doors & think it's a shame that so many duct jobs are out there with central return systems.
You have what you have though.
I would have transfer grills in the cieling with flex installed between them to maintain privacy for the bedroom if possible.
With insulated boxes & flex sound transmission through the duct will be less than any undercut door or direct pass through a register.

[pimy]

Do your returns have any frame to hold the filter,do the swing open to replace the filter/

Yes, they swing open to replace the filter. They don't have a frame to keep the filter trapped. The filter rests directly on top of the return grill. I was using twist ties with the pleated filters before I switched to velcro, and now the cheap filters. I'll try the hanger suggestion.

Thanks.