What Size Return Line From Bedroom To Air Handler

Under-sized Heating or Cooling Render Air Ducts

Postal service a QUESTION or Comment about too-small or blocked or undersized air conditioning, heating, and oestrus pump ductwork render air registers and duct connections

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Undersized render air duct trouble diagnosis & cure: this HVAC ductwork article describes the problem undersized return air openings - a problem that can be observed during inspection of the defects in return air ducts for heating or cooling systems (HVAC).

We also discuss duct troubles such as such as missing air conditioning cool air supply or render air registers, undersized air-conditioning duct openings, improper cooling duct routing, cooling (or heating) air duct corrosion, leaky air duct connections, lacking heating or cooling ductwork materials.

The photo above shows a small HVAC return air duct located on an interior building wall. Whether or not this return air duct is acceptable depends on how many such returns were installed in the building and whether or not the return air capacity is counterbalanced with the air handler and air supply ducting.

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UNDERSIZED OPENINGS - Under-sized Return Air Openings/Ducts

Photograph of an inadequate, under-sized single return air duct for a home.

Air conditioning & HEAT PUMP SYSTEMS, of which this is a chapter, describes the inspection of residential air conditioning systems (A/C systems) to inform home buyers, owners, and abode inspectors of common cooling system defects. Asbestos in or on HVAC ducts is a possible hazard for which we provide links to a split up document - run into "Asbestos HVAC Ducts" at below left.

Under-sized unmarried central air render: when we encounter a comparatively small single air return in a building, such every bit a 12X18" grille in a ceiling or wall, we suspect that insufficient return air ducts are present. This business is elaborated next.

The photograph shows an nether-sized single air return for a duct system serving an unabridged two story home. We increased the size of the return duct to lucifer the air handler and observed a doubling of the air period in the organization from this single improvement!

Central return air openings are very likely to be undersized when we see that the opening measurements are much smaller than the opening for air provided right at the blower fan.

At another case installation, the blower fan or return air plenum opening at the furnace was 20"x18" while the return air opening at the door to the utility room was 13"x13" (reduced further in effective size by a louvered screen).

When nosotros see amateur attempts to add supply or return air to a arrangement, such every bit observation of unanticipated openings in edifice walls, rough-sawn door undercuts, additional openings cutting in the return duct or plenum near the air handler, nosotros suspect organization blueprint issues. It is possible that previous occupants have found that the warm air supply was not adequate.

Should you confirm problems with inadequate heat delivery in some areas you'll want to consult with an HVAC engineer to make accurate measurements.

Door undercuts, central cool air render: If room doors are shut and not under-cut to allow air flow out of the room, the system'southward ability to cool the room may be reduced, sometimes significantly.

Endeavour running the cooling organization for 10 minutes with all room doors shut. So open a room door slightly and see what happens!

When a building uses a central render air grille and doors are not undercut heating some rooms may exist difficult - system cannot push cold air from the cooled or heated room back to the furnace.

While pocket-size amounts of new duct work (to take return air from the living expanse) are usually not plush, extensive re-ducting of air flow may involve pregnant expense

Reader Comments & Q&A

I can't say, Mike. Try reviewing the symptoms of inadequate render air given in this article. You volition see that any restriction in duct size volition cut airflow; shorter restrictions accept less outcome than longer ones.
Let me know the result.

Replaced 24 year old HVAC and enlarged HVAC return duct from 14" to 16", and then they reduced one end back to 14", is that ok?

TS am I right that you asked and we replied to this in email? The common causes are an air leak or an air menses constriction in the duct organisation.

I suggested trying to track downward the actual dissonance source, perhaps using foil tape on suspect openings or to change edges and angles in the air flow. Just making the return inlet larger would brand perfect sense if there was an air volume or flow mismatch, but if the dissonance is from air moving over an obstruction the size change may non help.

We simply had our A/C & Furnace replaced with a new unit that was very expensive and since the installation we are experiencing a high pitch whistling noise from the Return Air Plenum, the installers used the same plenum 12"x20" and bent a bunch of sheet metallic to suit to a larger render air grille 17"h 10 30" due west.

The company has sent their warranty tech out twice to no avail, they keep trying to make the return air plenum bigger by adding bent sail metal. Everything I take read says the return air plenum needs to exist much larger. I am looking for answers and getting very frustrated. Answers anyone?
three.5 ton Lennox A/C and Lennox variable speed Furnace (fan).

We just had our A/C & Furnace replaced with a new unit that was very expensive and since the installation we are experiencing a high pitch whistling noise from the Return Air Plenum, the installers used the same plenum 12"x20" and bent a bunch of canvass metal to adapt to a larger return air grille 17"h 10 30" w. The company has sent their warranty tech out twice to no avail, they keep trying to make the return air plenum bigger past calculation bent canvass metallic. Everything I have read says the return air plenum needs to be much larger. I am looking for answers and getting very frustrated. Answers anyone?
3.5 ton Lennox A/C and Lennox variable speed Furnace (fan).

Information technology feels like we are in a wind tunnel when the air is going up the cold air return vent. What causes this. Information technology is in the chamber

Short,

I've seen and heard metal panel bangs, clunks, and thunks that can be a startling heating system dissonance hands traced to just what you lot observed. When the fan starts upwards the system is at to the lowest degree initially a bit air-starved creating a vacuum on the return side of the system. A powerful fan tin too crusade the same noise past bulging out rather than in sheet metallic components on the supply side of the heating or cooling arrangement.

If the system is truly air-starved then information technology makes a lot of sense to add more return air inlets since non only volition you be curing the first-upwards or shut-downwards BANG noise in the duct and air handler system merely you'll also improve the effectiveness and efficiency of the system.

If the problem is a powerful fan at start-upward simply no air-starved concerns, and so I would add reinforcement U-channel to terminate flexing sheet metal noises.

If the organization is non air-starved, a fan control that ramps upwards the fan speed improves the situation but that's non a normal control.

Running the fan always on the lower speed defeats the purpose of having a multiple speed or variable speed blower fan in the first place: different speeds for varying needs.

When you take to leave the a blower compartment door open and so it'south a pretty proficient indicator that the arrangement needs more return air. Some other similar test I make is to wait until the blower has been on for 5 minutes or more than, so open up the air handler blower compartment door almost 6" and let go. If the door SLAMS close with a powerful Bang and then the arrangement is probably air starved.

I've installed a new 2 phase variable speed furnace in my basement, the air return is above it in 1 central
register on the master floor about xxx x 12. I have plant that when the furnace starts it sucks in the metallic air return panels in the basement that lead into the back of the furnace. I added another heating vent to the system into
the basement, merely have not increaased the air return yet. I have also turned the downwards speed of the fan to the lowest information technology will go, so now it ramps up slower. those 2 items take helped a lot. still I demand as well to leave the front end of the furnace door open up for additional air, otherwise it all the same sucks in the metal render. I was told to put bracking inside the render, which is an option, another pick I idea would be to add together another render to the other side of the furnce with another opening and filter. A furnace man came out and said that would piece of work, but wanted some others ideas and opinions. Thank you in advance, e-mail to cws56501@yahoo.com

TS am I correct that you asked and we replied to this in e-mail?

I suggested trying to track downwards the actual noise source, maybe using foil tape on suspect openings or to change edges and angles in the air period.

Just making the return inlet larger would make perfect sense if there was an air volume or menstruation mismatch, but if the noise is from air moving over an obstruction the size modify may not help.

We only had our A/C & Furnace replaced with a new unit that was very expensive and since the installation nosotros are experiencing a high pitch whistling noise from the Return Air Plenum, the installers used the same plenum 12"x20" and bent a bunch of sheet metal to adapt to a larger return air grille 17"h 10 30" w.

The company has sent their warranty tech out twice to no avail, they proceed trying to make the render air plenum bigger by adding bent sheet metal. Everything I have read says the return air plenum needs to be much larger. I am looking for answers and getting very frustrated. Answers anyone?

three.5 ton Lennox A/C and Lennox variable speed Furnace (fan).

It feels similar we are in a wind tunnel when the air is going upward the cold air return vent. What causes this. It is in the bedroom

Curt

Please run into an expanded answer to your question now establish

at BANGING NOISE at AIR HANDLERS or in DUCT SYSTEMS

Curt,

I've seen and heard metallic panel bangs, clunks, and thunks that can be a startling heating organization noise hands traced to just what you observed. When the fan starts up the organisation is at least initially a bit air-starved creating a vacuum on the render side of the system. A powerful fan can as well cause the aforementioned noise by bulging out rather than in sheet metal components on the supply side of the heating or cooling arrangement.

If the arrangement is truly air-starved then information technology makes a lot of sense to add more return air inlets since not only will y'all exist curing the start-up or shut-downwardly BANG noise in the duct and air handler arrangement merely you'll also improve the effectiveness and efficiency of the arrangement.

If the trouble is a powerful fan at start-up but no air-starved concerns, then I would add reinforcement U-channel to stop flexing sheet metal noises.

If the organization is non air-starved, a fan control that ramps upward the fan speed improves the state of affairs but that'south not a normal command.

Running the fan always on the lower speed defeats the purpose of having a multiple speed or variable speed blower fan in the first place: different speeds for varying needs.

When you have to leave the a blower compartment door open and then information technology's a pretty good indicator that the organisation needs more return air. Another similar test I make is to wait until the blower has been on for 5 minutes or more, then open the air handler blower compartment door nigh 6" and let become. If the door SLAMS close with a powerful BANG then the organisation is probably air starved.

I've installed a new 2 stage variable speed furnace in my basement, the air render is in a higher place it in i central
annals on the principal flooring about 30 ten 12. I have found that when the furnace starts it sucks in the metal air render panels in the basement that lead into the back of the furnace

. I added some other heating vent to the system into the basement, but have non increaased the air render yet.

I take also turned the down speed of the fan to the lowest information technology will go, and then now it ramps up slower. those ii items have helped a lot. however I need equally well to leave the front of the furnace door open up for boosted air, otherwise information technology notwithstanding sucks in the metal return. I was told to put bracking inside the return, which is an selection, another option I thought would exist to add another return to the other side of the furnce with some other opening and filter.

A furnace human being came out and said that would work, but wanted some others ideas and opinions. Thank yous in advance, email to cws56501@yahoo.com

If a Florida room has all block and casement windows equally walls that do not properly seal should the room exist air conditioned? It likewise has French doors that are non undercut and no render ductwork as this room used to be a porch/lanai.

I have a retangular air render grate and the duct work that connects to the heater is round, is this oK

Gerry

Good going sticking to your guns in the first place. If a cooling organization isn't dropping the temp below 78 something's wrong somewhere.

Low refrigerant (which ways there's a leak) tin can cause coil icing that would so block air catamenia and forestall cooling.

It is certainly true that if a cooling coil is leaking and is corroded and delicate the HVAC tech is probable to advise that information technology's non repairable. Tossing in the TEV may be a bit like shotgunning the repair diagnosis though it is often a less expensive arroyo to supplant several doubtful parts than to run up a beak with longer diagnosis.

Smashed Ac duct is important to fix and hopefully is a small improver.

Keep u.s. posted.

My Dual Pak HVAC unit 7 years former (Rheem) stopped supplying common cold air. I have coverage on my HVAC arrangement with AHS. The first visitor came out and insisted that since the outside air temp was 100 degrees and i was getting 78 degree supply air it was working fine. I disagreed with him and told him.

He then went up and said there was some insulation blocking the air duct and that was the problem. We even so were getting a lower book of air (tEmp 78 degrees. He went upwardly over again and after an hour said my TXV was not working ( he was basing this on the fact that the pressures didnt equalize at the compresser.

This tech finally simply went out to his truck and just left. AHS sent out another company and this teck said the shrader valve was leaking and the unit needed iii lbs of freon 22 and he also said the compressor needed a difficult start put on it along with a main contactor replaced. After he did all this the supply air temperature dropprd to 57 degrees.He said it should work fine now. I still didnt experience the air menstruation the unit has had since i had information technology installed 7 years agone. We used the unit of measurement for 12 hours and it ran constantly and past the late afternoon the temperature got up to 89 degrees in the rooms.

I called the company dorsum and the same tech came and checked the unit of measurement and said there was a leak somewhere and he couldnt notice it so he finally left without saying annihilation to my married woman. I called him and finally got thru and he said he was giving upwardly and he called AHS and they would be sending out another company.

This company came out and the technican said the unit was low on freon and there was a leak somewhere. He finally located the leak in the EVAP coil and said it couldnt be repaired so they would have to club one. He besides said he he thought the TXV wasnt working correctly and then information technology would also need replaced. The last affair he said was that my return air duct appeared to exist smashed a little lile someone may have stepped on it. He said they would have to replac the return air duct work likewise. He left and said someone would call

Is there a formula for area of duct return grilles necessary for heating simply in a two story house. Render grills needed on both floors?

Thanks

In my opinion, probably aye - every bit it'south a brake.

I agree that a likewise-slow air menstruation can contribute to coil icing.

Recall to check with great care the blower fan itself - a small amount of dirt on the squirrel cage blower fan blades may not look like much only I've found that dirt there can cut air flow by 40% or more than.

If a return duct has an elbow and connects to air handler at a smaller size than the wall intake opening, will the air menstruum exist compromised?
We are trying to solve a problem with freezing coils and have ruled out low refrigerant, dirty coils, dirty filter, blocked ducts and non functioning blower, valve (tXV) metering refrigerant was replaced.
Thanks.

400 sq.in is more than 160. If the filter describes the air handler return plenum size there's the answer. Probably not.

Is 160sq.in.of return vent adequate in a heat pump unit of measurement with a 20x20 air return filter.

Greg the efficiency of a furnace is indeed impacted by a constriction in the air commitment and render system, since to satisfy the thermostat while pushing air through a restriction means the system has to run longer. I'grand not certain information technology's a trivial calculation even so equally in my experience there are commonly multiple, overlapping efficiency reductions - so removing one does non necessarily assure that the boost in performance is exactly what you might hope or calculate.

Of all restrictions, however, a return air constraint is peculiarly ugly every bit it constrains *all* of the air movement through the air handler and on to the supply duct organisation. So a 33% reduction in return air is significant. Only with merely that single number I can't compute the actual real-earth effect. An interesting technical article on the complexity of computing the effects of changes in the air handling system is available from the United states of america DOE: See

Burdick, Arlan, "Advanced Strategy Guideline: Air Distribution Nuts and Duct Design", U.Due south. DOE (2011) at Bachelor electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Free energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831 - 0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:reports@adonis.osti.gov Bachelor for sale to the public, in paper, from: U.South. Department of Commerce National Technical Information Service 5285 Port Purple Road Springfield, VA 22161 telephone: 800.553.6847 fax: 703.605.6900 email: orders@ntis.fedworld.gov online ordering: http://www.ntis.gov/ordering.htm
Accept a expect at RETURN AIR, Increase

The air return duct is 12"x nineteen", 228 sqin, about 2/iii the surface area of the factory recommended air filter 14"x 25", 350 sqin. How much is the under sized return air duct reducing the efficiency of my new 95% furnace?

Question: is our heat pump return register likewise modest? What about noisy heat pump operation?

Nosotros recently had installed an American Standard ii ton 14 seer oestrus pump in an 1,100 sq ft basement. The basement is now finished but I continually questioned the installer on the size of the return.

The unit of measurement is multi-staged and when information technology ramps upwards the return is very loud. He installed a 14 by 20 inch return considering information technology fit neatly between the studs. He used viii ft of round flexible ducting to the air handler.

He also suggested I utilise the cheap thin filters for lower sound levels and better air flow. At that place is also a place for a xx past xx inch filter at the air handler which he said could be used instead of a filter at the wall render.

Could y'all delight permit me know how large the render should be and any pointers on filter use. - D.K.

Answer: Return duct eyeballing and guesstimating

A competent onsite inspection by an HVAC skilful normally finds additional clues that help accurately diagnose a problem or could certainly make a more than accurate statement about the needed return air inlet and duct layout. And I don't want to get too far into speculation by second guessing your installer since I don't know enough. That said, hither are some things to consider:

The size of the filter at the air handler gives a clue nigh the anticipated size of the air return that equipment manufacturer expected to take.
Your fourteen x 20 render air inlet = 280 sq. in. of air return;
Your filter size at the actual air handler is 20 10 20 = 400 sq in of air return
That means that at the air handler the pattern expected 120 more square inches than what you've got - or a 30% reduction in render air intake expanse.
A very crude test can tell you if the system seems to be return-air-starved: if we briefly open up a cover or case at the air handler by a few inches to admit free-flowing air into the air handler and and then let the cover get and information technology "SLAMS" back with great strength into place we figure the system is running with high negative pressure level and may exist air starved. (A door prophylactic interlock may prevent this test on your organization - don't mess with it or you chance having a finger cut off by a moving blower fan - let an good wait into this trouble]
Using a thinner filter may slightly improve air menstruation but in my OPINION that sounds a bit like a band aid and a bit inadequate if the system return air is xxx% less than design.
Probably an HVAC engineer skilful in this would give a more authentic accounting simply it sounds as if the return may be a bit pocket-sized. - longer distances of flex duct also can reduce air flow - installers effort to keep the duct distance from return air inlet to air handler as short and as straight as possible for best airflow If the arrangement is return-air-starved its operation will suffer and operating costs will increase.

Noise: I'thousand not sure what noise you are describing; if it'south airflow information technology could be related to the return and render duct

Question: return opening bigger than render ducts

(May 30, 2015) Duct size said:
I have a new system where the duct entering the render air plenum opening at the furnace is 16" ten 25" but information technology is fed by a duct between the joists that is only sixteen" x 12". Would it be a good idea to just increment the duct size so information technology extends beneath the joists, to say, 16" x 25" for case"

Answer:

Possibly. Showtime I'd check the system for inadequate return air since information technology'southward possible that the return inlet was just larger than needed.

Come across UNDERSIZED RETURN DUCTS

Question: amend air conditioning by increased fan speed, cleaning blower fan, clean air filter, remove duct obstructions before changing duct size

(June 15, 2015) Victoria G said:

I recently purchased a firm (60 years old) with central air. 3 ton unit. The habitation heating was fine this winter simply at present that we are using the key AC the house never goes downwardly more than 2 degrees. Information technology just doesn't cool the house similar it should. It appears from researching this it is 1.) bereft air returns AND insufficient duct work to deliver the cool air. I am reading central air requires larger duct work to deliver the absurd air than heat does ? Is that truthful ?

Respond:

Victoria

It may be possible to improve the performance of your central air conditioning arrangement by increasing the fan speed, changing to a variable speed fan, cleaning the blower fan assembly to improve its air motion ability, making sure that the air filter is clean, that no ducts are crimped or disconnected and similar measures.

Earlier even considering the costly change of duct size in a building I'd want to investigate not only those basic air flow improvements but I'd desire the system examined by an expert who could tell us if the air conditioner is working properly: what is the temperature drop across the cooling coil? is there an improper refrigerant charge? is the thermostat properly set and located? etc.

Question:

(July 9, 2015) GRF said:
I have a central air system in my house blower unit in the attic evaporator curlicue and compressor outside . it is a iii ton cooling capacity two stage system made by Bryant. my effect is the principal part of the house cools very practiced but our family unit room on the far terminate of the house is consistently v-8 degrees warmer . the room has cathedral ceilings. the incoming cool air vents are up high and the unmarried render vent is at same level in between the to incoming vents. my question is if I increased the size of the return air to the arrangement will i get better cooling in this room?

Reply:

Please see your question and our reply at inspectapedia.com/aircond/Return-Ducts-Registers.php

Question:

(Aug 5, 2015) Pdaz said:
3ton 1200 cfm blower,2 12x28 return registers,what size return ducts should I use? Returns are approx. fifteen/xviii' long. Supply is sixteen" flexible 4' long to sheet metal plenum 40' foot long,get-go collars off of plenum are iii 6",1 9",4 seven",2 8" with respective flex from each to registers.

Answer:

Is there a question hither?

Question: can under-sized ducts crusade HVAC air conditioner or heater to brusque cycle?

(Dec 22, 2015) Emre said:
Is it possible for an undersized duct organisation to cause a heater or air conditioner to curt cycle

Respond:

Emre: in my view, yes, possibly and then. If back-pressure level causes overheating in the supply plenum a fan limit might shut downwards the system.

...

Continue reading at AIR FLOW Improvement, HVAC or select a topic from the closely-related manufactures below, or see the consummate Commodity Alphabetize.

Or see these

HVAC Return Air Improvement Articles

AIR FLOW IMPROVEMENT, HVAC
- AIR FLOW TOO WEAK
- AIR LEAKS in Render DUCTS
- LEAKY DUCT CONNECTIONS
- Annals & DUCT LOCATION
- RETURN AIR, INCREASE
- Render AIR REGISTERS & DUCTS - home
- UNDERSIZED RETURN DUCTS

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