Restricting air return cavities

838 Views 20 Replies 8 Participants Last post by user_12345a, Apr 3, 2020

OttawaDIY

Discussion Starter · Apr 1, 2020

Hello all!

First off I hope everyone is doing well and staying safe.

Recently purchased a home built in the mid-90's and now looking to do some work. There is a load bearing wall in between the kitchen and living room that I would like to make a pass-through in (not a full on open pass-through, but just remove the drywall and frame nicely around the studs which won't be touched). However after looking closer, I noticed that the location I would have to use for this would block 75% of the air return vents which are just using the bare wall cavities.

Like this:

| 1 | 2 | 3 | 4 |

| = stud

I would have to block off 2, 3 and 4 - leaving just cavity 1 open for return air for 2 upstairs bedrooms.

My doors are never closed anywhere inside the house except for one door to the basement, so I was thinking perhaps the stairway would be enough to compensate for removing those other return air cavities.

Does anything have any input they could please provide? Thank-you in advance!

1 - 20 of 21 Posts

yuri

· #2 · Apr 1, 2020

I would not do it.

You may have enough air thru the stairs but you may also create some dead air spots in upstairs rooms as the air may circulate differently or not at all there.

You may end up with cold areas and Ottawa winters while not as bad as Winterpeg can be really cold also.

OttawaDIY

Discussion Starter · #3 · Apr 1, 2020

Thanks for the response!

So after some more looking around... I found out where those 4 wall cavities go to the air return.

1 - spare bedroom
2 - spare bedroom (using as office)
3 and 4 - to living room

So, by blocking 3 and 4 it won't cause any issue since I'd be blocking it above the living room vent return anyways. #1 would still be left fully functional, so could I just move #2 over to use the same vent as #1? (hope that makes sense)

Basically my office and a spare bedroom I never use would share the same wall cavity for the air return. All the other returns in the house come in at a different place and wouldn't be touched.

Thanks!

See less See more

yuri

· #4 · Apr 2, 2020

OK.

Beware if you block off some active returns then the air velocity will increase in the others and it could make the registers vibrate and make a singing/howling noise if they are metal.

Use wood ones if that happens or bend the fins slightly.

user_12345a

· #5 · Apr 2, 2020

Do not remove upstairs returns to go more open concept, you will regret it so much especially if you have a/c!

HVAC systems get ruined by renovators - removing returns, covering up supply vents.

It's not worth it.

Reactions: 2

stick\shift

· #6 · Apr 2, 2020

I will close vents to balance the house but I never cover or remove returns. I would find a way to re-route those returns or I would abandon the project.

Reactions: 1

OttawaDIY

Discussion Starter · #7 · Apr 2, 2020

Thank-you all for your input. Ends up I do not need to remove any returns, only have to move one vent in a spare bedroom to share the same wall cavity return as the other spare bedroom. Since that room is empty and never used, it should be ok.
Will keep an eye on the increased air velocity as yuri mentioned above and fix that if it becomes an issue.

user_12345a

· #8 · Apr 2, 2020

Ends up I do not need to remove any returns, only have to move one vent in a spare bedroom to share the same wall cavity return as the other spare bedroom. Since that room is empty and never used, it should be ok.

You would effectively be eliminating an upstairs return and splitting a pre-existing one.

Total return air from upstairs will be reduced.

Don't do it - you wouldn't remove a supply duct going upstairs and cap it off, then split another supply branch between two rooms so don't do it to the return.

Change your renovation plans or put a new return path elsewhere to replace what you're getting rid of.

roughneck

· #9 · Apr 2, 2020

Return airflow ability is directly based on duct size, among other things.
So say you have 2 200 CFM returns and combine them into a common duct, you aren’t going to automatically move 400 CFM.
Velocity is very important too, as already mentioned. Velocity and excess airflow cause noise.

3onthetree

· #10 · Apr 2, 2020

OttawaDIY said:
only have to move one vent in a spare bedroom to share the same wall cavity return as the other spare bedroom. Since that room is empty and never used, it should be ok.
Will keep an eye on the increased air velocity as yuri mentioned above and fix that if it becomes an issue.

You came for advice, got correct advice, and you're not listening to the advice. You are not increasing the amount of air pulled into the #1 stud space. It doesn't matter if you don't use the room.

Not to mention last millenium's penchant for pass-thru's are usually never added, existing ones are enclosed. So rethink.

beenthere

· #11 · Apr 3, 2020

Take a piece of duct tape. Tape your left nostril passage closed. Now go about your normal daily activities. You'll find you can't breathe as well as normal. That is what you are doing to your HVAC system by closing off that one return passage, without creating another one somewhere else.

Reactions: 2

Yodaman

· #12 · Apr 3, 2020

beenthere said:
Take a piece of duct tape. Tape your left nostril passage closed. Now go about your normal daily activities. You'll find you can't breathe as well as normal. That is what you are doing to your HVAC system by closing off that one return passage, without creating another one somewhere else.

Creative. I like that; hope I get to use that line some day! :wink2:

Reactions: 1

yuri

· #13 · Apr 3, 2020

You noticed he uses duct tape.

All good HVAC techs use that for repairs.:vs_cool:

Some Kleenex would do the job just fine but yeah duct tape will make a better seal.

Reactions: 1

OttawaDIY

Discussion Starter · #14 · Apr 3, 2020

Well the duct tape on the nose one isn't really a good comparison... since that's blocking 50% of the total air flow through the nose. Besides, just breath through your mouth and problem solved

Ended up finding a HVAC pro connection through a friend and he will be coming to do some testing first and then I will temporarily make the changes to the airflow and he will come back and test again.

Thank-you for your opinions! I'm hoping since no air is being forced into that unused room that what I would like to do would work. If not, will figure something else out.

user_12345a

· #15 · Apr 3, 2020

It won't work properly, you can't have two major returns off of one stud space - especially if it's another wall that's 2x4 instead of the 2x6 load bearing.

Give up on this plan.

OttawaDIY

Discussion Starter · #16 · Apr 3, 2020

user_12345a said:
It won't work properly, you can't have two major returns off of one stud space - especially if it's another wall that's 2x4 instead of the 2x6 load bearing.

Give up on this plan.

I'll let the pro look at it first.

yuri

· #17 · Apr 3, 2020

There is another workaround.

You don't want to starve your furnace for air BUT you could add another return vent in the basement if you have to.

You will get better circulation down there and solve the problem.

You will have less circ upstairs but it will still be safe.

And yeah get a Pro to check it to make sure it is not overheating later.

user_12345a

· #18 · Apr 3, 2020

OttawaDIY said:
I'll let the pro look at it first.

Does the house have a/c?

Without sufficient return on the second floor it simply won't cool properly with floors vents. Splitting a return cavity won't compensate.

Even with proper return air and supply, a lot of second floors are 2-3F warmer in the summer.

It could be okay for heating only if you do what yuri suggested.

There are two different problems removing return creates -

A lot of pros may not know anything about duct design - I don't believe it's taught to get a gas license in ontario.

See less See more

yuri

· #19 · Apr 3, 2020

There are workarounds.

You can put a ceiling fan in the upstairs and blow the heat down.

Duct design is kinda a joke in the resi HVAC biz and none of the companies I worked/work for ever did it. It was not taught at the gas fitter course either.

New home builders do it and then after that we do retrofits and make everything work however we can.

In Commercial and Industrial it is a must and they do airflow testing and balancing.

Point is if you are absolutely set on doing this reno and don't mind giving up some circulation upstairs you can compensate by putting in a ceiling fan for summer if necessary and adding a return vent in the basement to keep the furnace happy.

There are LOTS of houses with undersized sloppy ductwork and people get used to whatever they have.

See less See more

beenthere

· #20 · Apr 3, 2020

OttawaDIY said:
Well the duct tape on the nose one isn't really a good comparison... since that's blocking 50% of the total air flow through the nose. Besides, just breath through your mouth and problem solved

Actually, it a pretty good comparison. Since unlike your return system, your nasal passages are sized orrectly, for the amount of air the intake and exhaust. Unlike your current return system.

Breathe through your mount. That would be the same as just leaving your basement door open, and removing the blower panel so it gets more air.

when you have the "Pro" check your furnace before hand. Have him take the return static pressure in the blower compartment. And then recheck it after your alteration.

1 - 20 of 21 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.