"PVC" Duct In A Residential Forced Air System?

[Michael Thomas]

I'm going to be inspecting a residence Thrusday with "PVC" HVAC ducts"and was surprised to discover that there is such a thing as a PVC duct, for example:

PVC Duct Fume Exhaust Systems

However, as far as I can determine it is intended for use in exhaust hoods, scrubbers, etc.

There is also (I was aware of this) PVC coated metal duct for underground/slab applications:

Union PVC Duct | PVC Ductwork | Polyvinyl Coated Ductwork | Underground Duct | PVC Piping

but why use it in an interior location?

As the building as the recipient of a recent "complete remodel" I suspect that what I'm going to discover is that someone misidentified conventional or flex ducting with a white plastic VR at the exterior of insulation as "plastic duct", or worst case that this is is yet another un-permitted nightmare demonstration of contractor creativity and Sch 40 was used for some of the ducting.

But I don't want to be blind-sided if there is such a product as "PVC" duct; is there any sort of allowable exposed "plastic" supply or return HVAC ducting I could encounter at a residential inspection?

Thanks, as always.

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[Markus Keller]

I did a job up in Grayslake a number of years ago in a new subdivision. I was working for the owner on a completed house. The rest of the subdivision was in various stages of construction by the developer. All the houses were slab on grade.
1st floor ductwork was in-slab. It was some sort of PVC/PVC coated ductwork. Don't remember exactly. I was working there the day the village inspector came by for the build next door and signed off on it.
Ducts in the 2nd floor were mostly regular sheet metal. However, installers had pieces of the PVC ducts mingled in here and there. I guess if it fit they installed it. Not sure if that helps at all.
Not that anything the village signed off on was any good anyway. The developer used 1/2" and 3/8" cdx. One for the walls, one for the roof. Don't remember which went where. It was pathetic though.

[Darren Miller]

According to NFPA 90A

4.3.1.1 Air Ducts shall be constructed of iron, steel, aluminum, copper concrete masonry or clay tile except as permitted in 4.3.1.2 or 4.3.1.3.

4.3.1.3 is Gypsum board ducts.

4.3.1.2 refers to class 0 or class 1 rigid or flex ducts in accordance with ANSI/UL 181. I tried to research it but came up with nothing specific.

[H.G. Watson, Sr.]

I'm going to be inspecting a residence Thrusday with "PVC" HVAC ducts"and was surprised to discover that there is such a thing as a PVC duct, for example:

PVC Duct Fume Exhaust Systems

However, as far as I can determine it is intended for use in exhaust hoods, scrubbers, etc.

There is also (I was aware of this) PVC coated metal duct for underground/slab applications:

Union PVC Duct | PVC Ductwork | Polyvinyl Coated Ductwork | Underground Duct | PVC Piping

but why use it in an interior location?

As the building as the recipient of a recent "complete remodel" I suspect that what I'm going to discover is that someone misidentified conventional or flex ducting with a white plastic VR at the exterior of insulation as "plastic duct", or worst case that this is is yet another un-permitted nightmare demonstration of contractor creativity and Sch 40 was used for some of the ducting.

But I don't want to be blind-sided if there is such a product as "PVC" duct; is there any sort of allowable exposed "plastic" supply or return HVAC ducting I could encounter at a residential inspection?

Thanks, as always.

M.T.:

Regards "plastic" you might encounter, I suspect not PVC, but PE or rather HDPE, food-contact grade.

Unico, "SpacePak", AKDUCT/QADUCT (underground/above ground, respectively), and others.

UL 181 two categories, Class 0 or Class 1 (flamespread index less than 25 or greater than 25 & less than 50 IIRC).

Mechanical couplings w/ or w/o EDPM gaskets, low or no VOC bonding or thermal weldings in the field).

Whether or not accepted in the muni yet to be determined IIRC Illinois is "Home Rule" and oftentimes the authority ammends the various codes they may adopt (for example IIRC a particular muni in the NW burbs has expressly forbidden CDX of any kind be used for roof decking since before the I-codes were published).

Some potentially helpful links and two pdf brochures on "space pak" ducting to get you started:

AKDUCT Low VOC and no VOC sealants with plastic fittings for underground R-10.
QADUCT HDPE fittings R-8 above ground
UL 181 High-density polyethylene based duct system

clickable link to Scope for UL 181:
Scope for UL 181

See UL 181, Standard for Factory-Made Air Ducts and Air Connectors;

See also Related Scopes for UL Standards: UL 181A (Closure Systems) and UL 181B (Closure Systems).

See building materials pages @ UL regarding same, starting here:

UL | Air Ducts, Air Connectors and Closure Systems

Smart Pak System Duct
R-10 round High or Low velocity.

Unico and mini-split HPs may have similar non-metal ducting.


Here's a starting point for QADUCT (leading also to AKDuct):

Benefits - QADUCT, The Complete UL181 Plastic Ductwork

Attached two brochures on "SmartPak". EDIT: oops just one, the other was too large to upload. Here are direct links to the two files to d/l (I don't recall which was which) you could also peruse SpacePak; The Small Duct High Velocity Central Air Conditioning System yourself:


http://www.spacepak.com/modules/lit_...litFileID=1994

http://www.spacepak.com/modules/lit_...litFileID=2036


Remodels and touted as Green for new construction, and efficient. Google UL 181 and you'll come across much including california standards, limited acceptance, etc.

Hope that helps get you started.

H.G.

[Michael Thomas]

Interesting.... I'm used to seeing SpacePak installed with their "SP-25" metal, insulated flex:



connecting to sheet metal ducts:



and their HDPE ducting is new to me - many of the "SpacePak Type" installs I see are retrofits, and in some places it would be pretty difficult/impossible to snake rigid duct. Also, don't know if it would be acceptable in Chicago (where the property is located).

The QADUCT is completely new to me as well.

Potentially very helpful, thanks.

[Bob Elliott]

I would mention use of Spacepak vents in my materials section but sure would not see it as an issue.

Mush better and more efficient than sheet metal duct.
No issue using them in Chicago and in Chicago I am always running into converted floor joists.
Used SpacePaks at the old house when adding HVAC from a horizontal unit placed in the attic to replace the old space heaters.

[H.G. Watson, Sr.]

You're welcome.

[Ross Neag]

Hey Bob,

How are 4" high velocity ducts much better and more efficient than sheet metal--in a GENERIC question? Other than comfort, I'm interested to hear what that's based off of.

[Bob Elliott]

Hi Ross.
Personally I am surprised they are not seen more often.
Seems to me it all boils down to cost and efficiency. Here is a passage from the site link I am providing so you can find out more.

SpacePak can be installed into either new construction or an existing structure. Either way, the simplicity of SpacePak's sized-to-fit tubular ducts requires just a fraction of the installation time and cost associated with having sheet metal ductwork fabricated and installed.SpacePak - Small Duct High Velocity At-A-Glance

[Ross Neag]

I won't argue about their size and overall duct tightness, increased insulation over standard ducted systems, and and feasibility in retrofit applications. I will argue that I think it would be very hard or near impossible to properly install a house with 4" flex duct AND meet the appropriate ACCA calcs as well as the static pressures required by the manufacturer. I personally wouldn't want high velocity throughout a home.

[Bob Elliott]

I won't argue about their size and overall duct tightness, increased insulation over standard ducted systems, and and feasibility in retrofit applications. I will argue that I think it would be very hard or near impossible to properly install a house with 4" flex duct AND meet the appropriate ACCA calcs as well as the static pressures required by the manufacturer. I personally wouldn't want high velocity throughout a home.

Since I am not a trained HVAC tech I only see that they on the surface appear to be very good at what they do ,and perhaps the arguments should be left to those that are experts.
Sometimes as in arguments for not using PVC drain pipe and against Romex these arguments are based on unions wanting to keep labor costs up but feel free to let us know more, as I thought you were actually asking rather than setting up for an argument.

Need to get going for my association meeting tonight however will keep my eye on the thread to see what can be learned here.

Hope this all stays civil.

[Ross Neag]

Its off on a tangent anyway, no sweat. I need more info on their performance before I shoot my mouth off on things I haven't researched.

[Bob Elliott]

Its off on a tangent anyway, no sweat. I need more info on their performance before I shoot my mouth off on things I haven't researched.

Glad you do ,however with all the attics I go into most of what I see is the old fashioned hard to configure and uninsulated old fashioned sheet metal ducting.
These Spacepaks seem to be well suited for what the do with a higher insulation value and easier to install so I guess one can get all tech on it for arguments sake but the proof is in what's seen and I would have a hard time understanding why one would feel the sheet metal ducts with no insulation are a better option when running a second floor HVAC unit up in the attic for that purpose.

As mentioned I see them as a great alternative, but look forward to reasonable opposing views that can change my mind on anything.

[Ross Neag]

In response to what we DO find on a regular basis, I agree. Fully insulated trunk and branch lines, minimal leakage (for the most part), all of this is better than exposed sheet metal. Absolutely true. I think the rate of heat loss for an uninsulated duct is something like 4x greater in an attic in heating and cooling seasons, don't quote me.

R

[Michael Thomas]

Forgot to update on what I found: the "PVC HVAC ducts" turned out to be the PVC exhausts for CAT IV furnaces.

[Markus Keller]

I've installed a number of Spacepak systems in the past. Works well overall but system really needs to be properly figured and return air needs good distribution.
Waste of time and money in NC, good for retrofit where big soffits won't work.
As far as cost, it cost a fortune compared to using rectangular sheetmetal. Don't believe the hype about comparable cost.

[Bob Elliott]

I've installed a number of Spacepak systems in the past. Works well overall but system really needs to be properly figured and return air needs good distribution.
Waste of time and money in NC, good for retrofit where big soffits won't work.
As far as cost, it cost a fortune compared to using rectangular sheetmetal. Don't believe the hype about comparable cost.

Markus ,where does the extra cost come in?

[Markus Keller]

In quite a few areas
- Unless you specialize in Spacepak, which is a limited call, most guys don't keep a lot of spacepak materials laying around. It's expensive and gets lost or damaged before it gets used. As a tinknocker, there is always various ducts and fittings laying around to use on the next job. If working NShore or Goldcoast a lot then there's probably extra materials laying around. From that perspective it cost more.
- Ducting and the round registers aren't cheap
- Hole saws are far more expensive than sawzall blades. They also don't tend to last long when going through layers of old oak and pine substrate.
- Labor is more because one is typically working hard at snaking the pipe for concealment and inside of stud cavities. This takes a lot more time than a main trunkline and runouts.
Unless you have a boiler or architectural/space issues. It's a little difficult to justify the cost. Nice system, I like spacepak but I consider it more a system to be installed when you need it for its advantages rather than using it as a standard install.

[Bob Elliott]

In quite a few areas
- Unless you specialize in Spacepak, which is a limited call, most guys don't keep a lot of spacepak materials laying around. It's expensive and gets lost or damaged before it gets used. As a tinknocker, there is always various ducts and fittings laying around to use on the next job. If working NShore or Goldcoast a lot then there's probably extra materials laying around. From that perspective it cost more.
- Ducting and the round registers aren't cheap
- Hole saws are far more expensive than sawzall blades. They also don't tend to last long when going through layers of old oak and pine substrate.
- Labor is more because one is typically working hard at snaking the pipe for concealment and inside of stud cavities. This takes a lot more time than a main trunkline and runouts.
Unless you have a boiler or architectural/space issues. It's a little difficult to justify the cost. Nice system, I like spacepak but I consider it more a system to be installed when you need it for its advantages rather than using it as a standard install.

OK , Great for custom work when doing a retro fit is my take.

[Amanda Hill]

This is a somewhat dead thread, but it definitely grabbed my attention. I work for an industrial supplier that deals alot with PVC duct work. What's interesting is we've not seen much of a pick up in the residential space yet for this product. We felt it was mostly because of cost. It's definitely a great product, but expensive when compared to traditional ducting. We typically see it used in commercial applications like restaurants, oven exhaust systems, etc. So my question is, have you guys seen much of this in residential applications? It sounds like initially, no from this thread, but that was 5 years ago. We're curious if this product will catch on among contractors building homes, etc.