Thread: Unlined Return Duct

34 yr old home. Main return duct in center of first floor is simply framed and drywalled on the living space sides. There is a hole cut in the subfloor to allow the air to pass over and between floor joists to crawlspace mounted duct.

Can someone please post appropriate code references to why this is wrong in so many ways. Thank you.

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Bruce,

- M1601.1.1 Above-ground duct systems. Above-ground duct systems shall conform to the following:

- - 1. Equipment connected to duct systems shall be designed to limit discharge air temperature to a maximum of 250°F (121°C).
- - 2. Factory-made air ducts shall be constructed of Class 0 or Class 1 materials as designated in Table M1601.1.1(1).
- - 3. Fibrous duct construction shall conform to the SMACNA

Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards.
- - 4. Minimum thickness of metal duct material shall be as listed in Table M1601.1.1(2). Galvanized steel shall conform to ASTM A 653.
- - 5. Use of gypsum products to construct return air ducts or plenums is permitted, provided that the air temperature does not exceed 125°F (52°C) and exposed surfaces are not subject to condensation.
- - 6. Duct systems shall be constructed of materials having a flame spread index not greater than 200.
- - 7. Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
- - - 7.1. These cavities or spaces shall not be used as a plenum for supply air.
- - - 7.2. These cavities or spaces shall not be part of a required fire-resistance-rated assembly.
- - - 7.3. Stud wall cavities shall not convey air from more than one floor level.
- - - 7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8.

However, they did not do as stated above.

Originally Posted by Jerry Peck

Bruce,

- M1601.1.1 Above-ground duct systems. Above-ground duct systems shall conform to the following:

- - 1. Equipment connected to duct systems shall be designed to limit discharge air temperature to a maximum of 250°F (121°C).
- - 2. Factory-made air ducts shall be constructed of Class 0 or Class 1 materials as designated in Table M1601.1.1(1).

- - 3. Fibrous duct construction shall conform to the SMACNA

Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards.

- - 4. Minimum thickness of metal duct material shall be as listed in Table M1601.1.1(2). Galvanized steel shall conform to ASTM A 653.
- - 5. Use of gypsum products to construct return air ducts or plenums is permitted, provided that the air temperature does not exceed 125°F (52°C) and exposed surfaces are not subject to condensation.
- - 6. Duct systems shall be constructed of materials having a flame spread index not greater than 200.
- - 7. Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
- - - 7.1. These cavities or spaces shall not be used as a plenum for supply air.
- - - 7.2. These cavities or spaces shall not be part of a required fire-resistance-rated assembly.
- - - 7.3. Stud wall cavities shall not convey air from more than one floor level.
- - - 7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8.

However, they did not do as stated above.

Why? Doesn't say the plenum can only be made of gypsum. Doesn't say the framing has to be on the outside. Flame spread of nearly all framing is well below 200.

Thanks! I knew it was wrong but when the seller complains I want to be able to back up my opinion.

In this instance, the seller is a bank foreclosure so probably wont get much push back.

Thanks again for the quick response.

Originally Posted by Bruce Ramsey

Thanks! I knew it was wrong but when the seller complains I want to be able to back up my opinion.

In this instance, the seller is a bank foreclosure so probably wont get much push back.

Thanks again for the quick response.

Bruce, what part are you going to use to back it up?

Originally Posted by Vern Heiler

Why? Doesn't say the plenum can only be made of gypsum. Doesn't say the framing has to be on the outside. Flame spread of nearly all framing is well below 200.

Vern,

Didn't you read #7?

If you are going to do as you are implying, then you need to adhere to #7, and they did not.

Which is why I stated "However, they did not do as stated above." - they did not do ANY of the things stated in that section.

7. Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
- - - 7.1. These cavities or spaces shall not be used as a plenum for supply air. It is a return air plenum.

- - - 7.2. These cavities or spaces shall not be part of a required fire-resistance-rated assembly. I don't see anything here that requires fire rated.
- - - 7.3. Stud wall cavities shall not convey air from more than one floor level. Looks like it just conveys from first floor to crawl. But it's not a stud wall cavity is it.
- - - 7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8. We can't tell from the pic's but looks like it is tight from what we can see.

What did I not read?

It appears to me that they aren't using any wall cavity or floor joist space.

They have a duct installed between the joists. They are using the raised floor as a plenum.

As long as the plenum is sealed, I see no problem with the installation. Unless someone can change my mind.

Originally Posted by Wayne Carlisle

It appears to me that they aren't using any wall cavity or floor joist space.

Bingo!

As long as the plenum is sealed, I see no problem with the installation. Unless someone can change my mind.

Being as that is not stud cavities or the spaces between floor joists it needs drywall (or duct board, but drywall would be acceptable) on the inside of the studs, forming a sealed plenum, then there is that hole in the bottom, if not a duct then it needs to be sealed off too.

Originally Posted by Jerry Peck

Bingo!



Being as that is not stud cavities or the spaces between floor joists it needs drywall (or duct board, but drywall would be acceptable) on the inside of the studs, forming a sealed plenum, then there is that hole in the bottom, if not a duct then it needs to be sealed off too.

Nope!

Originally Posted by Vern Heiler

Nope!

Yep, it does.

There are two options for that: 1) drywall on the inside; 2) line it with duct board.

Is this going to be another of your pissing matches where you are wrong but refuse to admit it - like that dew point one? If so, you are wasting your time ... again.

So this particular installation is incorrect according to # seven?

Originally Posted by Jerry Peck

Yep, it does.

There are two options for that: 1) drywall on the inside; 2) line it with duct board.

Is this going to be another of your pissing matches where you are wrong but refuse to admit it - like that dew point one? If so, you are wasting your time ... again.

Wasn't wrong before and not wrong this time.

Not being right really jerks your chain doesn't it! Get over it, we still like you .

There is nothing that says a stud wall cavity has to be a single stud width. Wet walls are two or greater stud widths and the space between wall sheathing is the cavity. The pictured plenum is contained in a stud
wall cavity.

The plenum pictured at the beginning of the thread is common and approved by AHJ's across the country.

There is nothing unduly dangerous about this type of return plenum. If you are concerned about fire inside the plenum your way too late! The fire inside the room has already taken care of the insurance deductible.

Originally Posted by mathew stouffer

So this particular installation is incorrect according to # seven?

Correct.

That does not even have drywall in most of it, it is mostly exposed plywood.

Originally Posted by Vern Heiler

There is nothing that says a stud wall cavity has to be a single stud width.

It is not a stud "cavity" unless it is enclosed as a "cavity", as it is, the studs are open on one side, thus there are no "stud cavities" in there. The studs are "spaced" apart, with drywall on one side.

Originally Posted by Jerry Peck

Correct.

That does not even have drywall in most of it, it is mostly exposed plywood.

6. Duct systems shall be constructed of materials having a flame spread index not greater than 200.

Very unlikely to be over 200.

Vern, a question here. When you say "Very unlikely to be over 200."

Are you saying that the flame spread of material used is required to be over 200?

what is the flame spread index of plywood.

Depends on what kind you are talking about.

None of them have a flame spread index of more than 200 though!

3/8 SP is 100 to 105.

http://www.awc.org/Publications/dca/dca1/DCA1.pdf

Question to Bruce and Vern: Since both of you are NC inspectors, I'm curious how you are handling the recent NC HI reporting/effective code requirement for situations like this?
It seems there may be a paradox situation here when you believe/report an issue but when your only justification are the codes, it seems a potential situation for a complaint to the board could be created, unless you've followed the other code reporting requirements in the written report.

Originally Posted by James Skinner

Question to Bruce and Vern: Since both of you are NC inspectors, I'm curious how you are handling the recent NC HI reporting/effective code requirement for situations like this?
It seems there may be a paradox situation here when you believe/report an issue but when your only justification are the codes, it seems a potential situation for a complaint to the board could be created, unless you've followed the other code reporting requirements in the written report.

James, there is nothing wrong with the plenum as built. Not a safety or function problem, so I would not have mentioned it at all.

I don't quote codes in my reports but like having code requirements to back up an item reported if it is challenged.

It meets curret code and past code for as long as i can rember.

It is beyond the ability of installers and the cost to seal this type of duct to meet the air leakage standards of today. The most basic energy standards and codes that apply preclude the further use of this design.

Originally Posted by Vern Heiler

I don't quote codes in my reports but like having code requirements to back up an item reported if it is challenged.

I was curious to know in your opinion, if it created a conflict with the rules to call out an issue as a defect, in the report (no mention of code in the written report) and later the only defense are the codes. I avoid mentioning codes because I'm not a CEO but have relied heavily upon codes as a basis for justifing defect in the past.

Originally Posted by James Skinner

I was curious to know in your opinion, if it created a conflict with the rules to call out an issue as a defect, in the report (no mention of code in the written report) and later the only defense are the codes. I avoid mentioning codes because I'm not a CEO but have relied heavily upon codes as a basis for justifing defect in the past.

My interpretation is that you can not quote a code and be done. In other words can't say it doesn't meet code so needs to be resolved. We can state what is wrong and what the consequences of not resolving are. As code is a "minimum", as stated over and over on this forum, it makes code a good standard to use as justification. Just don't use it in the written report unless you want to open a can of worms!

Remember this is just my interpretation.

Originally Posted by Vern Heiler

My interpretation is that you can not quote a code and be done. In other words can't say it doesn't meet code so needs to be resolved. We can state what is wrong and what the consequences of not resolving are. As code is a "minimum", as stated over and over on this forum, it makes code a good standard to use as justification. Just don't use it in the written report unless you want to open a can of worms!

Remember this is just my interpretation.

Thanks, for your opinion. I've been wondering about this one, I haven't needed to defend a position yet but figured sooner or later it may happen. I don't know what brought about this rule change in the ledgislature but figured it had to be significant to get the state law makers off their backsides. The example in this discussion seemed like a good opportunity cause, depending on the inspector, it could be called defective or acceptable for a bunch of reasons.

HVAC return and supply systems are a pet peeve of mine. Our country is experiencing a dramatic increase in childhood asthma and general breathing disorders. There is a direct correlation between the increasingly tight building envelope and the rate of respiratory disease. The building industry implies that a HVAC duct system is a lifetime system, this position is ludicrous. Sewer lines require clean outs to keep the pipe clean; water lines require chlorination and periodic sampling to protect the public from water born pathogens; but the duct systems in our homes is considered to be a lifetime system with no provisions for reasonable access for cleaning or maintenance. It has even been suggested by some engineers that because the air going into the duct system is dirtier than the air coming out that there is no reason to worry about the air quality. The EPA does not recommend cleaning residential ducts systems because they know it is more likely to damage the system and disturb more dirt than it cleans up. There is a tremendous amount of politics involved in this issue. Should You Have the Air Ducts in Your Home Cleaned? | Indoor Air | US EPA
and NADCA - National Air Duct Cleaners Association

The typical person breathes in 100 pounds of air into his lungs every day. All this dirt in the air is filtered out by the lungs and nasal passages and stays in the body for some time. Our children spend most their time indoors in front of the boob tube breathing this stuff and we wonder why they are sick.

Generally speaking the air quality community is beginning to recognize the endemic problems associated with the lifetime, no maintenance duct systems and pressure the code community to acknowledge the importance of cleaning and maintaining residential duct systems.

Every inspector has seen filthy ducts in the attic and rats living ducts in the crawlspace. Mold is down played as being inconsequential but antidotal evidence tells me that when I open an infected cabinet and inhale a whiff of its mycotoxins, I am sick for the rest of the day. I know mold is bad for children. Mold is definitely a health safety issue regardless whether or not the lawyers/scientific can show a causal effect between mold and disease-. We have to look to the World Health Organization for good information instead of our own EPA.

Sorry for the rant. Duct system is a broad topic that needs to be reported as a system and not as specific items. Flame spread is is inconsequential when compared to the performance of the system.

Brad Deal CIEC

The EPA does not recommend cleaning residential ducts systems because they know it is more likely to damage the system and disturb more dirt than it cleans up.

Brad, my understanding is that they do not recommend duct cleaning because testing confirms that the air is dirtier after duct cleaning than before. Maybe that is what you were saying or maybe I have misunderstood you or the EPA.
Also, cleaning access for duct systems around here is very simple since there are access points at every outlet. Since I am not in the air, mold, or duct cleaning industry, I might not understand what you are getting at. Care to elaborate?

There is a direct correlation between the increasingly tight building envelope and the rate of respiratory disease...I like your thinking Brad....
It has been a code requirement for at least 18 years that fresh air is to be introduced into the house when a house is of unusually tight construction. I am in houses almost everyday that exceed the Energy Star infiltration rates and the lack of fresh air exchangers is a mute point. Every new house today if built to code is tight. I just am suprised at the lack of concern.
I have been told that because the houses do not get electric outlet gaskets under the plates, and the front door opening during the day ,that's plenty of fresh makeup air.
I get a kick out of how much we care assuring dilution air for appliances and not for humans.

Originally Posted by Richard Pultar

Every new house today if built to code is tight.

I've been telling that to people for 10-15 years, and here since I joined as the occasion arises. I say that because of the next thing you stated:

I get a kick out of how much we care assuring dilution air for appliances and not for humans.

Look at the combustion make up air requirements and everyone looks at the sizes interconnecting the rooms, etc., and fails to recognize this (which I have also pointed out many times in the past):
- M1702.3 Unusually tight construction. Where the space is of adequate volume in accordance with Section M1702.1 or Section M1702.2, but is within a building sealed so tightly that infiltration air is not adequate for combustion, combustion air shall be obtained from outdoors or from spaces freely communicating with the outdoors in accordance with Section M1703.

As you stated, that applies to most new construction homes with the new codes.

Most new construction is "unusually tight construction", which means combustion make up air needs to be obtained for outdoors, not the interior.

- UNUSUALLY TIGHT CONSTRUCTION. Construction in which:
- - 1. Walls and ceilings comprising the building thermal envelope have a continuous water vapor retarder with a rating of 1 perm (5.7 ⋅10-11 kg/Pa ⋅ s ⋅ m2) or less with openings therein gasketed or sealed. (Jerry's note: All openings are required to be sealed by the energy codes for air infiltration and exfiltration.)
- - 2. Storm windows or weatherstripping is applied around the threshold and jambs of opaque doors and openable windows. (Jerry's note: Weather stripping is required around all window and doors.)
- - 3. Caulking or sealants are applied to areas such as joints around window and door frames between sole plates and floors, between wall-ceiling joints, between wall panels, at penetrations for plumbing, electrical and gas lines, and at other openings. (Jerry's note: Caulking / sealants are required and applied around all windows and doors, at penetrations, etc.)

"Unusually tight construction" basically states the way each house is required by code to be constructed.

No matter how tight you make it there is always air infiltration, Bath vents (new const. typically 3 bath vents), dryer vent, attic access and sometimes range vents. These are not sealed.

Here in Kansas City (home of SMANCA)


I agree with vernthis is a type of plenum i see on slabs and crawls a lot.

Peck - Where does it say the drywall needs to be on the inside.

Originally Posted by Jim Luttrall

Brad, my understanding is that they do not recommend duct cleaning because testing confirms that the air is dirtier after duct cleaning than before. Maybe that is what you were saying or maybe I have misunderstood you or the EPA.
Also, cleaning access for duct systems around here is very simple since there are access points at every outlet. Since I am not in the air, mold, or duct cleaning industry, I might not understand what you are getting at. Care to elaborate?

My whole point is that there is no way to access many duct systems (at least here in California) much less clean them. The registers only provide partial access and there is no way to reasonably confirm 100% of the duct is clean. The registers are not designed to be an access for cleaning. There is a growing opinion in the air quality group that one should be able to "eat off the ducts," that is to say no visible dirt.

When a duct is enclosed inside a wall, or between floor joists, or the ducts are some kind of insuflex with 20 year old duct tape holding it together, there is no reasonable way to clean the ducts. Who knows what is in these systems. The EPA is careful about recommending duct cleaning because many time the ducts are worse after cleaning, not better. If the EPA told the truth about ducts and their relationship to respratory health there would be a major nation wide scandal.

So we have a code approved duct systems that can only be described as a lifetime system, never to be cleaned or looked at, ever, until the house falls down, or the children die from asthma. Codes are retroactive, someday they will address this issue. NADCA is already addressing this issue.

Look how hard it is to access most cooling coils and plenums in residential systems. Commercial duct systems require cleanouts and access panels. Cleaning and maintenance is a very low priority.

Try cleaning a piece of drywall or plywood, maybe, try cleaning a duct where the interior is lined with fiber board for noise suppresson or insulation, impossible without removal. The whole industry is designed for profit with little concern for our children.

Brad Deal