Return Air Filter - No Ducting

[ag99]

Just purchased a 5 year old house. Went to change the air filter on the bottom floor and noticed that there was no ducting behind the filter... just the inside of some interior walls (studs and drywall). Doesn't seem right to me but need some educated opinions. Should there be ducting? Thanks.

Anthony

[coolguysfl]

It was common place on old installs to use interior wall spaces etc as a chase for return air (ready made ducting). This is no longer accepted as the smoke & flame rating far exceed the min. mechanical code in most of the USA. It's further aggravated by an illusion of proper air duct sizing as the grill appears adequate but the max wall space behind it is a 3.5X12 greatly restricting proper air flow.

I'd recommend you seek out a professional for his opinion, it may be very cost effective to make modest changes and reap substantial benefits.

[dash]

Originally posted by coolguysfl
It was common place on old installs to use interior wall spaces etc as a chase for return air (ready made ducting). This is no longer accepted as the smoke & flame rating far exceed the min. mechanical code in most of the USA. It's further aggravated by an illusion of proper air duct sizing as the grill appears adequate but the max wall space behind it is a 3.5X12 greatly restricting proper air flow.

I'd recommend you seek out a professional for his opinion, it may be very cost effective to make modest changes and reap substantial benefits.

Ditto!

[Black Adder]

I don['t know if it was only on older installs that this was done, We still see it all the time on new installs in our area. Pretty common practice for the 35 years I have been in the trade.

[jmac00]

Originally posted by Black Adder
I don['t know if it was only on older installs that this was done, We still see it all the time on new installs in our area. Pretty common practice for the 35 years I have been in the trade.

I would agree with this assessment. I'm kind of curious as to how you would get return air into a basement if you DIDN'T use the space provided by the wall studs??? The wall space would be 3.5" x 14.5, thats the equivalent of a 7" round pipe at a .08 S.P. or 165 CFM. (okay it's actually a little more than a 7" pipe)

I do a lot of new construction and using the wall stud space is common practice, actually it's the industry standard around here ( western NY )and I pass code EVERYTIME. i HAVE NEVER BEEN "SHOT DOWN" because I used a stud wall space as a return air. Personally I don't think the inspecters give it a second thought

NOW!!!!! lets be practical? Around here we DO NOT have mold issues like they do down south or in a more tropical climate. We don't have nearly the humidity problems they do down south. SO those in the south may have different parameters as to how they do things.

just my 2¢ worth

[kewlguy1]

Duct work is nice but I've seen many jobs using bays in basement ceiling joists for returns. They seem to work ok.

[coolguysfl]

JMAC00 - I understand, as I said some parts of the county still allow this practice. I have frequently found 24X24 RAFG "ducted" via a wall 3X12 or 3 X 16 stud space.

I don't pretend to have all the answers and there are lot of variables from job to job. Frequently we build chases or build outs in closets to allow proper duct sizing. Certainly the overpaid architects bail on duct designs leaving it up to the lowly HVAC guys to figure out how to cool & heat a home.

You'd have to question though -- if the min. NFPA flame & smoke for ducting is 25 / 50 why in the world would a stud frame pass?

If we have any mechanical inspectors on line maybe they could enlighten us.

[Edited by coolguysfl on 10-16-2006 at 05:57 PM]

[jmac00]

Originally posted by coolguysfl
JMAC00 - I understand, as I said some parts of the county still allow this practice. I have frequently found 24X24 RAFG "ducted" via a wall 3X12 or 3 X 16 stud space.

I don't pretend to have all the answers and there are lot of variables from job to job. Frequently we build chases or build outs in closets to allow proper duct sizing. Certainly the overpaid architects bail on duct designs leaving it up to the lowly HVAC guys to figure out how to col & heat a home.

You'd have to question though -- if the min. NFPA flame & smoke for ducting is 25 / 50 why in the world would a stud frame pass?

If we have any mechanical inspectors on line maybe they could enlighten us.

ya I understand where your coming from and you are correct. Half the inspectors around here are on ego trips and make things up just to aggravate everyone. As far as Architecs go, don't even get me going on that group of complete flaming morons. some day a guys going to walk up to me and say "hi, I'm an Architec"..........I'm just going to punch him in the head.

[dash]

Check out Manual D and you'll see how restrictive joist and stud spaces can be to air flow.

[smokin68]

Is it on a stand, using a closet door or similiar as a return? I've seen this, and there is no R/A restriction, just not as controlled as a ducted system IMO. Also have seen R/A grill through a wall, but airhandler is sitting on top of a plenum box. Duct isn't always necessary, just prefered. Many FLA installs have no R/A ductwork.

[jmac00]

Originally posted by dash
Check out Manual D and you'll see how restrictive joist and stud spaces can be to air flow.



YA!!!!!! Thats why we get paid the big bucks, to figure out the friction losses and to design a system to over come those problems.

So if your against using the joist and stud spaces for return air, How would you get return air from a second floor to a basement?

[deejoe]

I absolutely agree with jmac00. There are no problems getting return back to a unit using the stud or joist paths. The qualified installers still use this method in many,many ,civilized areas of N. America.

btw, coolguysfl; a standard stud(2x4 @16"o.c.) space is 3.5" x 14.5",NOT 3.5" x 12".

[dash]

First,in Florida ,the code prevents joists/stud spaces from being used for ducts.

To get ducts from one floor to another, space must be provided,could be by making a closet a little smaller.

[Carnak]

Originally posted by jmac00

Originally posted by dash
Check out Manual D and you'll see how restrictive joist and stud spaces can be to air flow.



YA!!!!!! Thats why we get paid the big bucks, to figure out the friction losses and to design a system to over come those problems.

So if your against using the joist and stud spaces for return air, How would you get return air from a second floor to a basement?

I lined a lot of joists in my day jmac, and we had some pretty tightly sealed homes in Canada.

There is never a problem getting return air from the basement with all the potable water and wiring going through the joists, around the headers used as an 'endcap' for the lined joists, or where the return trunk picks up the air from the lined joists.

Ever see the door to the basement stairs shut when the furnace starts?

Every new home with framed construction in Canada has a sealed vapour barrier at the ceiling plane(attic) or at the rimjoist along the outside walls.

From a humidity standpoint, in winter time up north, the cold air is not going to sweat when it contacts something at room temperature. In cooling, the dewpoint up North could very well be a lot lower than what your customers set their thermostats at.

Using the building cavities as a return can be very problematic in a humid climate especially when the outside air wants to sweat when it touches room temperature surfaces.

[pstu]

Is there a professional issue about whether the wall space should be fitted with a liner to seal it?

If you Northern guys don't have to worry about duct leakage then I am jealous.<g> My understanding is if there is significant return leakage vs. supply leakage to unconditioned space, there could be an issue of operating the house at slight positive pressure vs. outdoors.

This is something to seek in the hot-humid South where I live. I have seen numerous good references in building science to support this. But it is just the opposite, something to avoid in heating climates. In fact operating the house at a slight negative pressure is the safer way to avoid (humidity) problems in the North. Am I right?

Always appreciate your insight -- Pstu


P.S. My own house was built with a non-ducted chase for one of two returns. I am told this is not good practice unless well sealed, I made sure to seal it as best I could.

[Edited by pstu on 10-16-2006 at 11:09 AM]

[dash]

here's what I've heard about homes in the northern states that have joists and studs used as ducts.

1.They are often too restrictive ,due to turns that are not condusive to to air flow.

2.They leak when not sealed air tight.

3.Leakage to unconditioned spaces ,causes the usual issues.

4.Leakge within the conditioned space,can cause lack of air flow to those runs farthest away or on the second floor,while overcooling/heating the basement and closer areas.

[jmac00]

Originally posted by dash
here's what I've heard about homes in the northern states that have joists and studs used as ducts.

1.They are often too restrictive ,due to turns that are not condusive to to air flow.

2.They leak when not sealed air tight.

3.Leakage to unconditioned spaces ,causes the usual issues.

4.Leakge within the conditioned space,can cause lack of air flow to those runs farthest away or on the second floor,while overcooling/heating the basement and closer areas.

AGAIN!!! you are going back to design & engineering and the skill of the installer ( and I am goooood) LOL

each room is supplied with "X" amount of air. With that knowledge we KNOW how much return air is necessary. if you design for that, and the friction loss's involved there is no system or home that can not be heated or cooled properly.

[deejoe]

I certainly agree with jmac00. Return air is often thru joists, studs, wall cavities, etc ,etc. And it can sure cut down on a lot of $$$ unnecessary expense in materials, such as duct and fittings,etc.
And this panning, joist lining, wall stud space in no way will ever adversely effect the workings of any heat/cool unit when installed properly.
A few years ago, most edcucated tin knockers had the know-how to install a "tight" and neatly installed duct system. There was no need for any of this present day 'caulking gook' and tape in order to make a system function right.
Most(not all) present day duct bashers are just that.... (duct bashers) and they don't have the know-how or the perserverance or patience it takes to do a proper "Tight" job.
I can remember when many new homes, many even 2 story houses had no return air DUCTS whatsoever except for some joist lining and a main ducted return into the unit.
And it sure cut down on the overall cost compared with to-days prices.
And the bottom line was these heat/cool systems worked properly and efficiently even without all this unnecessary return ducting.

[ag99]

Thanks for the replies guys... I'm in San Diego near the coast so weather is not extreme. I took some pics of the return but can't figure how to post them. It seems really tight as the area above the vent seem blocked off... air would have to take a right or left before going up to the attic. I assume a pro could look at it and measure air flow to determine if design is a problem, yes?? Also, I noticed saw dust and crap inside this area. I'll clean what I can but you think that might be a problem (my boy has some alergy issues). Thanks again for the replies.

Anthony

[dash]

So, design for the air flow required by Manual D,following manual D sizing procedures.


















Then use the joist/stud space that's available,regardless of what size Manual D called for,be it larger or smaller??Leaves me wondering about that!

[jmac00]

Originally posted by dash
So, design for the air flow required by Manual D,following manual D sizing procedures.

Then use the joist/stud space that's available,regardless of what size Manual D called for,be it larger or smaller??Leaves me wondering about that!

Yaaa! whats your point there zippy. What are you going to do, go into a $750,000 home, tell the general Contractor ( GC ) that he has to spend $500 and add a wall so you can drop a cold air trunk, Bwhahahaha, good luck with that, we will be able to identify you by the Estwing hammer sticking out your head :D besides, if the architec had done HIS JOB this would be a moot point. But 9 times out of 10 when you look at a blue print the Architecs, cover there butts with 3 simple words......."installed by others" :(


look, lets be practical here. How we run the return air is WITHIN the National Mechanical Code. If done properly, the system will work, and work very well. It's economical and efficient. Sometime the physics of the structure don't allow us to get "all" the air that we would like, back to the furnace from a particular space. So that "lost air" has to be made up someplace else, otherwise it will be difficult to balance the system.

On one hand this ain't rocket science ~~~~on the other hand, it is.

We can debate whether the use of a stud wall space is a good idea or not, the reality is, it's allowed, prefered ( because of costs) and it works. As soon as the Code nazis change things, give me a call. I'll be more than happy to call my GC and inform him of the huge bill he's going to get on the next project because of the extra duct work and labor that will be required.

[azulikit]

I have found over the years that systems have less and less btus to meet the requirments of todays units...It is nore inportant than ever that a system be installed with the proper airflow. Inn the "old days" there were 55,000 btu compressors in 4 ton units...now you are lucky if there are 46,000 btus. Now that I am older, and want a few headaches as possible..... I will pass up a job if proper space is not provided for the return especially. 3.5 X 14.5 wall chases would NEVER work for me....

[jmac00]

I will pass up a job if proper space is not provided for the return especially. 3.5 X 14.5 wall chases would NEVER work for me.... [/B]

well to each his own, It's my guess you NEVER do new construction. I hope you have enough work coming in that you can pick & choose what you want to work on. Good luck with that

[deejoe]

[QUOTE]Originally posted by azulikit
..... I will pass up a job if proper space is not provided for the return especially. 3.5 X 14.5 wall chases would NEVER work for me....
************************************************
unless your installing duct to huge Palace sized rooms,then we must assume nothing will ever work for you.

Having access to a return 3.5 x 14.5 (Approx 50 sq in.) from any average size room,being supplied by an 5" or 6" run would be more than adequate.If, for instance it needed more return than the one stud space could offer, then use another adjoining stud space ,now you have approx 100 sq inches of return and you can install a suitable sized return grille for that amount of opening.

Return air using adequate sized stud spaces, adequate sized joist spaces,etc, etc, is one of the best thing to happen since the discovery of fire.

In a normal residential home,for the Return air, I could NEVER imagine using ALL metal duct, fittings, including transitions, reversibles,offsets,etc (you name it) in place of adequate stud and joist spaces.
Just the thought of the added restriction, static gain and increase in air turbulance makes me shudder.
Hip-hip hooray for the joist/stud spaces of today.

[dash]

Originally posted by jmac00

Originally posted by dash
So, design for the air flow required by Manual D,following manual D sizing procedures.

Then use the joist/stud space that's available,regardless of what size Manual D called for,be it larger or smaller??Leaves me wondering about that!

Yaaa! whats your point there zippy. What are you going to do, go into a $750,000 home, tell the general Contractor ( GC ) that he has to spend $500 and add a wall so you can drop a cold air trunk, Bwhahahaha, good luck with that, we will be able to identify you by the Estwing hammer sticking out your head :D besides, if the architec had done HIS JOB this would be a moot point. But 9 times out of 10 when you look at a blue print the Architecs, cover there butts with 3 simple words......."installed by others" :(


look, lets be practical here. How we run the return air is WITHIN the National Mechanical Code. If done properly, the system will work, and work very well. It's economical and efficient. Sometime the physics of the structure don't allow us to get "all" the air that we would like, back to the furnace from a particular space. So that "lost air" has to be made up someplace else, otherwise it will be difficult to balance the system.

On one hand this ain't rocket science ~~~~on the other hand, it is.

We can debate whether the use of a stud wall space is a good idea or not, the reality is, it's allowed, prefered ( because of costs) and it works. As soon as the Code nazis change things, give me a call. I'll be more than happy to call my GC and inform him of the huge bill he's going to get on the next project because of the extra duct work and labor that will be required.


You can do it any way you choose,just pointing out the disadvantages .Code will likely force the change in the near future,but you could be the progressive contractor and offer homeonwers and builders an option,for a better way today.

[jmac00]

Code will likely force the change in the near future,but you could be the progressive contractor and offer homeonwers and builders an option,for a better way today. [/B]


Progressive??? you have absolutly no clue how much money your adding to a job...........You have never dealt with a builder have you???? They go nuts if you tell them it's going to cost another two bucks because you had to use differant screws

well actually it's pretty easy to figure out, your DOUBLING the duct work, not to mention adding anywere from 30 to 60 hours to a job.(depending on the size of the home)

on the other hand, it's a good way of giving a builder either a good laugh or a hart attack. either way your going to be looking for another builder.

well this thread has pretty much run it's course, you kids have fun

[skeeter_22]

Maybe I'm being a little too practical here...but I noticed that the original poster made no mention of performance or efficiency problems with his return air or the system as a whole. In fact, he didn't seem to notice anything till he went and changed the filter. I do a lot of residential service as well as run the new construction side of my brother's heat and air company. I catch myself sometimes over thinking or complicating duct work because of my service side. The two should not be mixed! Not very cost efficient at all. Any tinkering I find myself spending several hours on is beyond 95% efficiency the system would get with a simple standard design. Thats about $55-60 bucks a year down here.
If my father on the other side of the U.S called and wanted my advice on this, I would ask him the same thing I'm asking now..."Noticed any problems?" I wouldn't tell him to call and spend b/t $500-1000 to "repair" this if it isn't such a problem that he didn't even notice it at purchase or since.