My HVAC contractor has proposed using duct board instead of sheet metal for all of the heating and cooling ducts. Anybody out there know the pros and cons? Thanks!
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Upgrading the footings and columns that support a girder beam is an opportunity to level out the floor above.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
I was told that the ductboard deteriorates in time....how much time I am not sure. I just bough a spec house a year ago and it seems the only place they used sheet metal is at the registers. I guess that is the con, the only pro i can think of is that the ductboard is cheaper, but then again how does it compare in price if you have to replace in x number of years..... not sure if it has a better r value or insulation rating......
Its faster to install, self-insulating and quiet. It
will last as long as the fiberglass insulation you have everywhere
else in the house. No expansion/contraction noises.
It is a bit more expensive. Last place we built, used it only
where insulated ducts were necessary. Used regular metal for
all the returns.
Like most products out there, a range of price and quality exist. Find out exactly what line they intend to use. Good duct board is, well, good. Cheap duct board is a problem waiting to happen. An important feature to look for is the lining. Neoprene is a good choice. Anti-microbial is a good investment, as well.
Pros: Ease of installation including sealing and more uniform insulation, light weight, quiet.
Cons: Cost, potential for poor installation/craftsmanship, vulnerable to physical damage, more potential in a badly sized/designed/setup system to grow things.
Tim
Tim's answer is the best one. The question isn't just how long it will last but "Is it healthy?"
Warning... the following is my opinion and you are free to disagree if you wish.
I consider it all junk and will not install it. I also refuse to put insulation inside my sheetmetal ducts for the same reasons. I have seen way too mch crap growing on this stuff besides the fact it is an excellant place for dust to collect and break off in chunks o blow out in your face.
For me it's externally insulated sheetmetal or flex duct all the way or get someone else to do your work.
PS. Tim... my hard drive crashed so I have been on very little lately. Didn't mean to ignore you on the boiler thread we had going.
Used surplus whiteboards for my ducts. Enameled steel layer is just at the UMC min thickness (15.6 mil) for fire code, cuts almost like plywood (goggles a MUST), stiff, nails up like plywood (plyU sealant on joints), quiet in HVAC operation, even cleaner than galv. metal, nice Al foil/osb exterior to staple insulation to if needed.
Sounds interesting. Any pics? What is this board and where do you get it?
WHW:
I'll post a pix if I remember when I get home tonight.
Got the stuff free at local aerospace surplus yard, somebody else had already stripped off the aluminum frames or else they would have come with a "dollar bill" attached, most were 4X6 foot pieces.
WHW and Tim -
Your comments on ductboard is very disturbing and I am very concerned.
Our recently installed central a/c (all in the attic) uses this stuff.
We were told there shouldn't be any concern for loose fibers if it is installed properly.
Our trunk lines are made with duct boards and all branches are fed with insulated flex tubes (R-6).
One selling feature for the ductboard is quietness and indeed they are.
I did ask about metal trunk lines and the installer talked me out of it.
They are very reputable in our area and did an excellent job sizing and configuring out system. Quality if installation was very good.
But my hunch always has been this somewhat unsettling feeling that something's going to go wrong one day, causing us to rip out everything and replace them with metal.
Alan
WHW:
Since you asked, here's a pix of whiteboard ducting, this is a transition from overhead return between 2 sets of joists to outdoor packaged 4T unit. Cost for section shown, about 50 cents., 2X4s off old pallets, polyurethane from garage sale at 50 cents per big stick. Drywall screw assembly. It ain't fine woodworking, but very quiet and can make fit anywhere.
What gives, I see the limit is up to 3 MB, but no attachment posted. Ach well, another time, gotta catch an early plane.
Hey, it did post, but at 151K when win/explorer said it was 91k in my files.
Can we post attachments of almost any size now, up to 3 MB at a time?? How long has this been possible?
Is Pro-Dek coming back, now that he can more readily communicate with customers plus share his neat pix?
Alan,
I remember when you posted a question about this. Ductboard is a fine product and not a health concern. Some have a preference for sheetmetal for various reasons. I prefer sheetmetal myself.
Unsealed ductboard is not common (I looked and cannot find a product that is not sealed). It has NOT been banned anywhere and no state, county or municipality, in this country, is considering such. Fiberglass is NOT a carcinogen, and you should not be overly concerned about loose fibers or as one idiot posted, about "eroding" ductboard clogging up your lungs. Have you seen any evidence of loose fibers in your house since the system has been installed? I doubt if you ever will.
As I posted earlier in this thread, the main concerns with ductboard are that: it can be expensive (as compared to sheet metal); is subject to installer skill (and what isn't?!); can be susceptible to physical damage if installed in an exposed location; and in an improper application (using ductboard in a natatorium or as exhaust duct would be improper applications) can be a place for microorganisms to grow. In a normal, residential forced air furnace/AC system, not a concern.
As with any air system, I would recommend that you use the best filters you can find to keep the coils and ducts as clean as possible. I use the AprilAire 8" thick, mechanical filter. 3M Filtrete 1000 is an excellent filter as well and fits a standard 1" filter housing. Lined duct and duct board are more susceptible to being fouled by dust than sheetmetal. Is this a major concern or a health threat? No.
It is a potential concern, that, from time to time should be examined. You may need to have the ducts cleaned every few years. You may not.
Edited 6/11/2002 8:49:30 AM ET by Tim
Hi, Tim -
Thanks so much for your reassuring reply.
Another concern I have is our attic has gone through gradual transformation, all in preparation for the cellulose blow-in.
This includes new electrical wires and reconfigured circuits, ridge and soffit vents, sealing up all holes into the attic, etc.
Luckily we have zero fiberglass in the attic - we have foil bags that are commonly found in houses built in the 1950s.
Without getting overwinded, I heard some reports of flex delivery tubes deteriorating in the hot attic and wanted to get everything, including most of the ductwork, under cellulose. This may help prevent premature failure of the tubes ?
I may be repeating a previously posted question - sorry.
The installer used better quality tubes - they told me R-4 is commonly used but they use only R-6 rated tubes with foil cover.
Should I be concerned with heat damage to the tubes or ductboard over time ?
Cellulose blow-in will not be done until later this year or next Spring.
As for filters, the ceiling mounted return houses a 24"x24" filter, which turns out is difficult to find in stores. They have everything but this size.....
I want to use the 3M filters and may have to mail-order them.
They gave us three spares and we're down to the last one.
We have a fairly dust-free household - no pets or wall-to-wall carpeting - so the filter isn't being worked overtime.
I'm figuring one filter change, maybe two, per A/C season is enough for our house. (Ours is A/C only.)
Other then the alarming note on potential problems with ductboard and tales of flex-tube failures (coming from the installer himself), we have been very happy with our installation.
Even with the unit in the attic the system is so quiet we have our kids' paper streamers and windsocks fluttering next to the ceiling registers as a visual clue.
Take care,
Alan
Alan,
I'll be honest with you on the longevity of duct board and insulated flex ducts in an attic: I don't know. You said that you had added soffit and ridge vents, that will certainly help. If it were my house, I wouldn't give it a second thought.
As far as the filter goes, the size (24x24) is not that common , but the rating or efficiency of the filter is more important than the dimensions. When you find a good replacement, buy a case. The frequency of replacement will have to be determined by your experience. Annual, just prior to the start of use, is a good starting point.
Tim
Thanks, Tim -
The stories of flextube failure comes from the installer that handled ours. Most of them have been with tubes that have the gray plastic covers, not the metallic foil wrap that they used in our house.
The outer plastic layer had deteriorated and was flaking off.
Yes, your suggestion of quantity purchase is a good one.
I've been wanting to do that but first I have to find a mail order source for Filtrete. I'm going ahead with their highest rated model.
I found a couple sources but if you know of a bulk supplier.....
I do appreciate the feedbacks you've been providing.
Alan
A company by the name of Air Handler sells filters through Grainger. A carton of 12, 24 X 24 x 1" fiberglass filters is $31.20. A better quality (i.e. more effective) paper pleated filter is $5.11/each in cartons of 12 ($61.32). More options are available. Look at http://www.grainger.com. I don't know what sizes Filtrete has available or who sells them in bulk.
In my house, during construction, I use cheap fiberglass filter(s) as a roughing filter upstream of a "dust" filter. When all construction is complete, I will use the AprilAire filter. The AprilAire mechanical filter cartridge housing (model 2200) accepcts standard 16 X 25 x 1 filters. I can stack several together, or use just one, depending on how much dust I create. During heavy "dust days" when the furnace has to run, I change filters as often as once a week. In "normal" service in my house (which includes 4 dogs and two cats) I change the "roughing" filter once every other week and the "dust" filter, i.e. the Filtrete 1000, once a month.
Tim
Ditto Wet Head Warrior.
A PC that crashed? Unheard of! I'm sure it'll come up again (the thread, not your PC).
When I looked into this situation a few years back the item which caused me to go with metal was the constant erosion of glass fibers from the duct board. These fibers lodge in the lungs and cause the same problems as asbestos ( read cancer). I also understand , though not absolutly sure, that glass fiber duct board is banned in California for this reason, and may be banned in other states in the near future.
If glass fiber erosion by the air flow is not a problem, then why do the manufacturers coat the insides of the product to try prevent it?
Ease of fabracation and sealing? How? With duct tape? Has anybody ever seen a tape hold anything longer than a few months? After a few years the supply air will be exhausting out everywhere but the supply regesters.
Spend a few extra bucks, go with metal sealed with a fiber reinforced mastic. If it is located outside of the heated envelope, inspect every joint yourself before it is covered with insulation. Your family will thank you for the fiber free air, and the gas man will damm you for the efficiency of you system.
One correction. It is illegal to use duct tape on these.