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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.

Return air inlet on second floor is too small

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 2018-11-13 by PKD

by (mod) -

PK

"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 the return air vent or inlet or ductwork is under sized you may be able to correct that problem by adding another duct serving the same area. It's easy to check at the air handler to see if the system is air-starved.

A simple amateur test is to open a door to the air handler briefly while the fan is running and then let it "slap shut". If it SLAMS! with force then the system was probably air starved.

Followup by PKD: how do I measure and get the right return air flow rate?

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 it hAs apparently never worked. How would I measure the air flow at the return vent.

This would at least show its not working. They have 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.

Reply by mod:

See these articles:


Why is upstairs zone of my A/C drawing return air from the basement even though the basement air is off?

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? On 2018-06-20 by Carl

Suggestion 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.


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