Using unlined wall cavity for return ventilation

[dougsturgess]

Our contractor is considering putting a return vent without any metal ductwork inbetween 2 studs. Sheetrock will complete the closed cavity.

This seems like it would promote mold growth in that cavitiy.

Is this safe to do or is it building/HVAC code to use ductwork in this situation.

Thanks


EDIT: no emails in forum posts

[Edited by Mod01 on 12-10-2005 at 02:33 PM]

[t527ed]

wall cavity is used all the time here in nj. i don't think i have seen a house built in the last 50 yrs that did not do this unless it was a attic system. have never seen mold growth in return ducts.

[dougsturgess]

Thanks for replying.

Just to clarify for me, you're saying it's standard practice to use a wall stud space as a return vent using the exposed 2x4 studs and sheetrock for lining instead of metal duct work?

[m kilgore]

We also do it all the time here in Nebraska. It works OK and most of the time there wouldn't be any other way to get return air.

If you want ducted return air then ask for a price for the upgrade. Most companies will do whatever is asked (for a price). Around here most homowners are more worried about losing 1 square foot of there house than having enough return air. Another thing you may want to do is seal the space as well as you can before drywall. The electricians and plumbers will drill through studs and plates which could cause return to be pulled from attic or such.

Its OK with codes here.

[dash]

Against code in Florida,for several years.

I wouldn't worry about mold(I've seen hundreds of them,no problem),I'd be more concerned about the small cavity,and fitting/turns used being restrictive,but if it's a small return and sized correctly it will be fine.

They do pull air from other studs ,so I'd seal it ,even if you just caulk the studs,just before drywall goes up.

[docholiday]

Its common practice here too, generally not a problem.
If they did it on the supply, that would be reason enough to strangle someone.

[jeep6275]

in iowa we do it all the time. it is one of our biggest sellers when changing out equipment. but even in knew const. we dont duct it.

[Pschneid]

It's commonly done but (NOT) on an outside wall. Where are you located?
Phil

[dougsturgess]

Thanks for everyone's reply. I live in Atlanta, GA.

The wall is an interior wall and the vent will be placed at door height on the wall. So the run will be from the vent, between the studs & sheetrock down to the crawlspace where it attaches to either flex duct or the original metal ducts.

[hearthman]

This is a ripoff way of doing things! It leads to imbalances, interzonal competition, and sometimes backdrafting. In order to get the system to work they have to oversize the equipment to compensate. It can cause air to suck under walls leaving the dust filtered by your carpets. You do NOT have smooth, aerdynamic ducts. They are anything but that. They are jagged, with crude changes in dimensions. The seams are not sealed so air can move laterally. It will take the path of least resistance. This often means air will stagnate in the far corners of the house while sucking too much air from areas closer to the air handler.

You should insist on sealed ducts throughout and proven with a Duct Blaster test.
IMHO

[markwolf]

It's been done that way since the eighteen hundreds that I know of.If you want metal ducted returns expect to pay alot more money to upgrade!

[Black Adder]

Hearthman, get a grip. Don't try to use scare tactics on the customers. Return air in unlined wall cavities has been used as long as there have been forced air systems. What is all the bs about oversizing equipment? What does that have to do with using wall cavity for return air? How many systems a year do you design? They must be awfully expensive if you are ducting everything the way you suggest. What is the difference between using the wall cavity (providing you have enough return air) or using the ceiling space above Tbar ceiling on a commercial job? This is also a very common practice. Many commercial jobs we do have engineered systems drawn in this fashion. Do you also duct all your return airs in the basement? If so why do they make "joist lining", is it any different using floor joist cavity than wall cavity?

[billygoat22]

Panning is a common practice, but its the primary source of air leakage in ducts. I've seen plenty with filters put in the grill and unfiltered, unconditioned air leaking into the panning behind the filter.

Make sure its substantially sealed. I used 4 tubes of caulk on one duct run once.

[bydabeach]

Energy Star in NJ does not allow panning. If a contractor is going to use panning, what are some guidelines?

1. No panning on outside walls?

2. Caulk the stud corners in the panned joists?

[davidr]

Originally posted by hearthman
It leads to imbalances, interzonal competition, and sometimes backdrafting. It can cause air to suck under walls leaving the dust filtered by your carpets. You do NOT have smooth, aerdynamic ducts. They are anything but that. They are jagged, with crude changes in dimensions. The seams are not sealed so air can move laterally. It will take the path of least resistance.


I have found these same issues in the field.
This is one reason we went to hard ducted returns in our installs & retrofits.

Many times returns installed in this manner are directly connected to the unconditoned space. Keep in mind all holes are not created equal once you put the driving force of a fan behind them. It is hard to control airflow when you have uncontrolled leakage on the ducts it is traveling through.

You will not see this leakage unless you are testing your duct systems, I prefer methods other than a duct blaster to obtain these values.

[trane]

Its done here all the time but you have to have a lot of stud cavities or get a larger return somewhere. Most new home floor plans don't give you enough rooms and wall space to get all the returns by using just the wall space without seeing grills all over the place.

Hearthman, Robo says that the return is not sucking air its being pushed back through the return ducts by the blower. Just had to through that in because there are several posts that seem to point to the fact that returns do suck. I'm still waiting on the answer David. LOL

[neophytes serendipity]

Ducted returns are not used in my area unless it is required by code.

Ducted returns may be better, but it does cost more for labor and materials. The duct can be less forgiving than a wall cavity for space requirements.

It is a good idea to run the crimp in the direction of airflow if you are going to duct those returns.

[AllTemp]

Taking rturn air from between the studs mean that theres going to be some sort of fitting on top of the wall in the crawl space/attic like the one I have pictured here...

I have the old RA can sitting there... Notice the large slots cut in the old return can and the sloppy ovaled duct hole! Thsi thing was installed as you see it in the attic uninsulated and had been pulling attic air for 16 years.

Customers coil was you guessed it packed with dirt!

http://www.alltemp-hvac.com/plenum.gif


On the same system the contarctor could not fit anything on the supply because a cieling joist sat right smack in the middle... You can see by the fitting they had ovaled two 10" collars, that was it.... Think they had air flow issues?

To the right but unfortunately cut off you can see the new SA can that has a nice large 16" collar. we headed out the joist to allow this...

This is an example of pure lazyness...
http://www.alltemp-hvac.com/OldSA.gif

Only problem I see in doing the RA in the wall is.. Will they properly seal the wall, stud channels, RA cans, ect... Or can they even get to them to seal them...

[davidr]

Originally posted by trane
I'm still waiting on the answer David. LOL

I am going to do my best to get by the office & pick up my hood today. Will hopefully have findings to post tomorrow. ;)

[docholiday]

In a system where your returns go up to an attic, I wouldnt suggest it for the reason above, its a matter of how you are going to mate it. If the return goes down the wall to a basement, then by all means it's fine.

All the cavity is, is a path for the return. If it's restrictive then it's poorly designed long before you ever got to the actual installation.

[trane]

[QUOTE]Originally posted by AllTemp
[B]Taking rturn air from between the studs mean that theres going to be some sort of fitting on top of the wall in the crawl space/attic like the one I have pictured here...



None of the returns go into the attic here. They all are in the wall towards the top plate. Something that I commonly see in replacements is using a total of 4 stud spaces and two 6x30 R/A grills for all the return. Most can't understand why I have to add more because its always worked before.

[hvac hero]

We use interior walls to pull return all the time here. Returns are always down low & the supplies are always in the ceiling. The furnaces are located in the attics here. We've even had to use some exterior walls when the floorplan is so open that theres no interior walls for a family room. Code wants us to put a 3/4 sheet of styrofoam pushed against the outside wall to insulate it. I dont like doing it this way but I've done houses that it was the only possible way.

[neophytes serendipity]

Originally posted by AllTemp
Taking rturn air from between the studs mean that theres going to be some sort of fitting on top of the wall in the crawl space/attic like the one I have pictured here...

Only problem I see in doing the RA in the wall is.. Will they properly seal the wall, stud channels, RA cans, ect... Or can they even get to them to seal them...

All of your issues deal with a crappy install, not problems with using joist/wall spaces for return air.

There is a difference.

[AllTemp]

Originally posted by neophytes serendipity

Originally posted by AllTemp
Taking rturn air from between the studs mean that theres going to be some sort of fitting on top of the wall in the crawl space/attic like the one I have pictured here...

Only problem I see in doing the RA in the wall is.. Will they properly seal the wall, stud channels, RA cans, ect... Or can they even get to them to seal them...

All of your issues deal with a crappy install, not problems with using joist/wall spaces for return air.

There is a difference.

Exactly, that why I am pointing this out... Who would have thought that a reputable Lennox dealer wold have done this kind of hack nstallation. But they did the entire neighborhood looks like this ****!

I hopefully pointed out there's nothing wrong with a wall return cavity if done properly. Man un educated people may look at what I found and see nothing wrong with it.

[dash]

A single stud wall space ,is often too small for the duct and grille size used,just bad design ,but that's what we find.

The fittings to get into the wall are often too restrictive,as shown in post by alltemp.


One other problem is the drywall is not sealed to the studs and leaks ,often allowing air from the wrong places,and if filter grilles are used,that air goes unfiltered to the equipment.

[docholiday]

It's a regional thing. Again in a home with the system in the basement, there is really no objection since the ductwork is In the conditioned space. If you have a crawl or an attic, then ducting is the only way to go and of course it shouls also be sealed and insulated as well.

Frankly a few nails and rough cuts are still 10 times better than a peice of flex snaked around with all it's friction. For the most part, the drywall surface is smooth on the backside. A standard stud space is 16 on center which yeilds you a 14.5" x 3.5" duct. Double stud spaces are often used when this is not enough. For those who use a central return, then a duct to the return is probably better.

Up North, you will often find more than a few returns. One in every bedroom and most other rooms except the kitchen, utility and bathrooms. For instance a standard bedroom may have a 14x6 return grille, the master may even have a 30x6 as would the living room. In areas of the south where crawl spaces are more often the norm, then one or two central returns are more prevelent and often are ducted.

Electrical wiring is another issue. you may cross a panned return with a wire but may not run the wire with the space.

As far as returns being pushed or pulled it really is neither. High pressure goes to low pressure, its really pretty simple. No matter the duct system, the key is making sure airflow is not restricted and friction limits are observed.

[Carnak]

Originally posted by hearthman
This is a ripoff way of doing things! It leads to imbalances, interzonal competition, and sometimes backdrafting. In order to get the system to work they have to oversize the equipment to compensate. It can cause air to suck under walls leaving the dust filtered by your carpets. You do NOT have smooth, aerdynamic ducts. They are anything but that. They are jagged, with crude changes in dimensions. The seams are not sealed so air can move laterally. It will take the path of least resistance. This often means air will stagnate in the far corners of the house while sucking too much air from areas closer to the air handler.

You should insist on sealed ducts throughout and proven with a Duct Blaster test.
IMHO

If you have any holes in the top plates sealed so you are not sucking any attic air in, the stud space of an interior wall is fine for return air.

[wally01]

OK in Mich. Most every thing goes to basement ductwork. Hearthman, most respectfully, what is the difference between using stud space vs. panned off joist space? We use both here. How do you guys attach panning? I used to pound my fingers but now use a little cheap air stapler fromNorthern Freight. Works awesome. No accidental dents. No mashed fingers. And it doesn't distort the metal causing panning noise.