Thread: Furnace Ducting Work?

I need a little help on this furnace duct work, the supply air just runs under the vanity then comes out with a cover. This has to be a fire hazard installation? Yes one can argue that the probability is low for the vanity to catch on fire but I still think this setup is not acceptable in anyway. How strong would you comment on something like this?

Cheers.

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Improper and unprofessional installation of HVAC supply duct/register beneath vanity cabinet in ____________ bathroom (duct empties into space beneath vanity cabinet and is not connected to supply register - repairs needed)

How do you figure that this installation could cause a fire?

Is anyone aware of any codes or standards that would disallow this installation?

That could be essentially considered the same as the spaces between joists or studs, and this is what the code says about the use of those spaces:

(underlining and bold are mine)
- 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.

That could be essentially considered the same as the spaces between joists or studs, and this is what the code says about the use of those spaces:

Jerry,

If you were a building official, would you strrrrrettttcchhhhhh the code that far?

Would you write that up in a home inspection report? If so, what would you write?

I seriously doubt that arragement will start a fire but it is certainly not very efficient (conditioned air not blown directly into the intended space; heating/cooling vanity instead of room).

Originally Posted by Brandon Whitmore

If you were a building official, would you strrrrrettttcchhhhhh the code that far?

Brandon,

Go back to my post and read the 7 choices given under:
M1601.1.1 Above-ground duct systems. Above-ground duct systems shall conform to the following:

Then YOU tell me which that would meet if not choice 7.

Hint: None of them.

That is why THE DUCT needs to go all the way to the register, which is what I was pointing out in choice 7 (as not being allowed in choice 7).

Would you write that up in a home inspection report? If so, what would you write?

I would fail it on a code inspection for not meeting code.

I would write it up on a home inspection for not working as intended as it was never intended, never even ALLOWED to work as such as it was never ALLOWED to be constructed as such.

Why on earth would you NOT write it up?

Jerry,

My answers will be written in red.

- M1601.1.1 Above-ground duct systems. Above-ground duct systems shall conform to the following: Yes, this is an above ground duct system.
- - 1. Equipment connected to duct systems shall be designed to limit discharge air temperature to a maximum of 250°F (121°C).N/ A to this discussion.

- - 2. Factory-made air ducts shall be constructed of Class 0 or Class 1 materials as designated in Table M1601.1.1(1). I don't consider the under cabinet area a duct.
- - 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.N/A
- - 6. Duct systems shall be constructed of materials having a flame spread index not greater than 200. I don't consider the under cabinet area part of a duct system.
- - 7. Stud wall cavitiesThis is not a stud wall cavity and the spaces between solid floor joistsThis is above, and not between solid floor joists, so nothing below is applicable 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.

Why on earth would you NOT write it up?

Where did I write that?

The toe kick in the cabinet should have been ducted. Normally it's done in the rough in stage and cut back as needed to fit the vanity. I have seen plumbers rip them out because their vanity doesn't fit though.

Originally Posted by Brandon Whitmore

Jerry,

My answers will be written in red.

- - 2. Factory-made air ducts shall be constructed of Class 0 or Class 1 materials as designated in Table M1601.1.1(1). I don't consider the under cabinet area a duct.

- - 6. Duct systems shall be constructed of materials having a flame spread index not greater than 200. I don't consider the under cabinet area part of a duct system.

Okay, if not a duct, then what, a plenum?

If so, then I am back to this as the space IS being used as a "plenum" ...

- - 7. Stud wall cavitiesThis is not a stud wall cavity and the spaces between solid floor joistsThis is above, and not between solid floor joists, so nothing below is applicable 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.

Okay, if not a duct, then what, a plenum?

If so, then I am back to this as the space IS being used as a "plenum" ...

Why couldn't the end of the duct be where the boot meets the floor?
This installation isn't much different than all of the beds, dressers, couches, etc. being installed over heat registers.... The only difference is that one is temporary and the other isn't.

PS: The IRC's definition of a plenum is a chamber that forms part of an air circulation system other than an occupied space being conditioned.

Originally Posted by Brandon Whitmore

Why couldn't the end of the duct be where the boot meets the floor?
This installation isn't much different than all of the beds, dressers, couches, etc. being installed over heat registers.... The only difference is that one is temporary and the other isn't.

PS: The IRC's definition of a plenum is a chamber that forms part of an air circulation system other than an occupied space being conditioned.

If they put the supply grille on that duct and let it discharge under the cabinet, which would be open to the room, what you describe would be okay within the minimum limitations of the code as the supply register would be properly mounted "to the duct".

However, as shown in that photo, and as you have stated, "the duct" is 'back down there' at the floor, while the supply register is 'up here' at the bottom of the cabinet, which means 'the space between the the duct and the supply register' is now "plenum".

Would putting the supply register on the duct as it is supposed to be make it operate any better? Yeah, some, as the supply register would have its vanes adjusted so as to direct the air toward the open area at the front of the cabinet as best possible instead of just having the open duct blowing uncontrolled up against the bottom of the cabinet.

Would I like that? Nope. Would it pass muster for minimum code? Yes, if done properly (if there is a way to 'properly' do something which is inherently 'improper').

If they put the supply grille on that duct and let it discharge under the cabinet, which would be open to the room, what you describe would be okay within the minimum limitations of the code as the supply register would be properly mounted "to the duct".

Is a supply grille/ register required at the end of a duct? I believe so, but can't remember for sure. Jerry, you know the code much better than I do, and probably wouldn't have to look it up-- is it?

Originally Posted by Brandon Whitmore

Is a supply grille/ register required at the end of a duct? I believe so, but can't remember for sure. Jerry, you know the code much better than I do, and probably wouldn't have to look it up-- is it?

Depends ...

The duct needs to be properly terminated, which would either be by installing a supply register (or return grille if referring to a return duct) or connected to a plenum.

Additionally, the duct work is a "system" and that "system" includes the directional control provided by the supply register vanes which direct the air in the required direction from the duct. The "system" is designed around various factors, including the CFM air flow, the location of the duct/register in relation to the space, the direction of air flow from the duct/register, and many other aspects. Leaving the supply register off and allowing the supply to dump uncontrolled amounts of air into an area which is basically dead-ended, and then cutting in an opening, is making that into a plenum, which needs to meet the requirements of a supply duct in this case.

Thanks.