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Photograph of a return air register for commercial office spaceHVAC Return Air Improvement FAQs
Q&A: how to Diagnose & improve the flow / volume of return air

HVAC return air improvement questions & answers. :

This article series explains how to increase HVAC system return air to increase heating or cool air output by improving the flow of return air to the air handler. This article describes problems with return air inlet size, location, and ductwork.

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FAQs: how to Increase Return Air Flow in Heating or Air Conditioning Duct Systems

Photograph of added return air cut at basement AHU also may draw flue gases from nearby gas fired equipmentThese questions & answers about air conditioning or forced air heating system return air diagnosis and improvement were posted originally at RETURN AIR, INCREASE - be sure to review the advice given there.

On 2019-06-08 03:16:29.142910 by (mod) -

I don't know, that sounds like what we call a short circuit in the air system. Perhaps you could have had some photos and we can figure it out. One photo per comment.

It is not the case that all air ducts have a damper installed.

On 2019-06-07 23:17:46.876917 by Chris Carson

Why would there be a duck from the output of the air handler to the return Plenum With a waited manual damper

On 2019-06-07 16:34:30.065548 by Ronese

Ive been looking for the damper lever i dont one nowhere do all HVAC have them or not the unit blow air but not a full flow and no in all vents none of them are blocked could the coils need clean in air conditoner system and its leaking water from side but in go the the drain pipes also the ducts are clean what can cause this

On 2019-04-20 20:50:58.735999 by Sola

Please, What are the effects of a corroded return air duct in an air conditioning system?

On 2019-03-31 15:30:50.637428 by (mod) -

Start by looking through the causes for blocked air flow given on the page above. Then let me know what questions remain.

On 2019-03-30 11:13:47.440587 by manikandan

Hi friends . i have facing one issue in a smoke system . there is two no's duty fan connected in same plenum box and suction duct connected from the plenum box into public area . Each fan capacity is 6000 lps. both fan are duty fan . so design flow is 12000 lps. Getting actual flow only 7500 lps. I measured the airflow by running individual fan that time getting 6000 lps . so fan performance is ok...while i running both fan at a same time i getting 7500 l/s only . Fan suction from public area ( Open area , air circulation is there). Please help me to get a solution

On 2018-11-17 01:15:40.831569 by Anonymous

they said that they coiuld only use 6" as there wasnt room in the closet for the lsrger size. They removed the larger duct work snd put in new return vent box but its appsrently never worked. How would I measure the air flow at the return vent. This would atleast show its not working. They hsve been doing maintenance snd have been saying its working fine but when I pointed it out after finding it wasnt working they then said it was because of the duct size.

On 2018-11-13 23:02:12.344714 by (mod) -

PK

I don't understand the situation either.

Too large for the space doesn't seem to make sense to me if something is too large for the space that it can't physically be in there. There is a code issue with installing an air conditioner or heat pump that is oversized in capacity for the building that it serves since such a unit is likely to not work correctly

in particular it may not be capable of dehumidifier in the indoor are adequately. A blocked duct should simply be corrected. If it's under sized you may be able to correct that problem by adding another duck serving the same area.

On 2018-11-13 22:00:18.035917 by PKD

I had new Trane hvac installed and have just found out return air vent on 2nd floor never has worked since ductwork only 6 ". This was never picked up by installer even post installation maintenance services. My question is why did they put in an air handler that was too big for space so they couldnt put larger ductwork in. The old unit worked better.

On 2018-09-02 00:25:09.800183 by (mod) -

Blocking the air flow can cause cooling coil icing that would reduce air flow and cooling output.

Other than that I can't guess what's meant by "not operate properly"

On 2018-09-01 22:54:19.694394 by Flash

I have 2 12 x 12 return vents in my floor in two different rooms. App built-in closures around them and put in bigger filters could this cause my heat pump not to operate properly????

On 2018-07-24 18:05:41.770087 by (mod) -

Sorry John I don't understand the situation. Perhaps you can add some images.

There is definitely a "correct" rotation direction for the squirrel cage blower fan rotating body itself, and there will be arrows marking air direction on some equipment.

On 2018-07-23 23:21:32.468757 by John

I have a new 4 ton installed and after inspecting the evaporator/ fan enclosure I noticed the squirrel cage holding the fan motor's intake pointing to the closed space of the enclosure as opposed to facing the incoming air from the return. My installer states that it doesn't make any difference which way the intake faces, but common sense tells me that the air flow hitting the winding of the motor and the brackets that support it reduces the flow of the system. What is your opinion on this ?

On 2018-06-20 21:57:21.920568 by (mod) -

Carl

I emphasize that I can only guess as I know almost nothing about your situation, but perhaps there is inadequate return air ducting or a too-small return air register for the system that's running. I'd start there.

On 2018-06-20 21:44:03.226666 by Carl

I have duel fuel system with 2 zones. The basement system is in off position with the return sealed off, however my unit is pulling air into basement...can't see any obvious breeches in return plentym. Any suggestions as to how I can find what is creating this issue?


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