Greetings,
Hopefully I am not asking a question that has just been answered a month ago. I tried to do a search but I am new to the board and am not the best on computers.
I am looking to install a heat pump this summer and am trying to decide which type of duct work is the best to go with. Can anybody tell me the advantages or disadvantages to duct board, flex duct, and the metal duct work?
I read the choosing duct work article that is on Fine homebuilding and it directs you to using as much straight metal as possible. The installers that I have spoken to have given me some different opinions. One gentlemen said duct board will fall apart in 10 to 15 years so we should stick with metal and flex duct. Another gentlemen swore by duct board and said it is quieter and will hold up just as well as metal.
I want to make the right decision because I want to do this once and only once. Any help would be greatly appreciated.
Thank you in advance.
Adam
Replies
Adam,
Welcome to Breaktime!
Ductboard
Depending on your area, the primary disadvantage of duct board is that it is hard to get a decent quality name-brand product, like Johns-Manville. It is susceptible to physical damage. It is not impervious to liquids. It is quite. It is easy to work with. It is light and is well insulated. If protected from rodents, children and water will last longer than vinyl siding.
Sheet Metal
Is easy to get, has hundreds of standard fittings, is durable and to a small degree water proof. It can be difficult to work with for the inexperienced and can be noisy if poorly installed. It will sweat and requires external insulation. It will last longer than brick siding.
Flex Duct
Wire reinforced thin plastic covered usually with 1" of fiberglass insulation. It is cheap. It is easy. When used sparingly it can speed installation of a sheet metal system. Usually the province of hacks, it (and those who propose its use) is to be avoided.
You entered no info on your profile so we don't know in what part of the world you are. IF you live in an area of frequent/constant high humidity, I would go with galvanized sheetmetal. IF your doing this yourself and can wield a utility knife like a wizard, go with the duct board.
Thank you, This is the type of information that I am looking for. While I do most of the work on my house myself, this is one area that I am going to contract out. I know for the heat pump to work correctly we have to have the duct work precise.
I live in Pennsylvania. I'll try to get my profile updated as soon as I figure out how. I'm better with a saw than I am with a computer.
Thanks again.
Edited 6/26/2008 2:35 pm ET by Adam33
I don't know much about duct board. What we went with was rigid metal, trying to keep flex duct to just the last 5 feet or so at a register. We ended up with more here and there (original installer was a hack).
The big thing is just getting the whole duct system sealed up well. The best way to measure this is via a 3rd-party 'duct blaster' test. Should cost $100 to $200. For a new system, a good installation should leak at 0.05 cfm per square foot of conditioned area. Just be aware (and the installer should be too) that, in addition to sealing duct/fitting seams, you need to have good attention to detail at the equipment and that the duct boots need to be sealed to the drywall.
The system also ought to sized correctly- cooling via ACCA Manual J, ductwork via Manual D. The former should take into account the actual conditions at your house (including a field measurement via blower door test of how leaky home is).
I'd be tempted to run from a contractor who was sizing via rule of thumb. The testing stuff may be new, so you should give the contractor every opportunity to understand what's involved so that it doesn't come as a (costly) surprise later.
FWIW, we put in a dual-fuel system w/ a heat pump. The heat pump has a dual fuel kit, but over the past 2 years it hasn't proven the greatest at locking out the heat pump where I'd like to (isn't consistent or at low enough temp for my preference). We have a Honeywell Vision Pro thermostat (highly recommended), and I have the outdoor sensor to hook up to it. Just need to find time to install it and take the dual-fuel kit switch out of the control circuit.
Here's a factsheet on the testing:
http://www.southface.org/web/resources&services/publications/factsheets/22blowdoor.pdf
Mrsludge,
Thanks for all the info. I had read about the testing on the duct work and personally agree that it is a great ideal. Unfortunately I have been able to find nobody in this area that does this. The closest I have found is a company that is 3 hours away. Unless I find somebody closer it doesn't look promising to have the system tested. Thanks for your help.
Adam
Right ... duct blast test is hard to find. Just do a good job and you know the test would come out OK.
My 2 cents: Avoid flex duct unless necessary ... and most times it is not necessary ... just makes the contractors life easier (and your job lower quality). There is a time and place for everything ... and most times it is not flex duct ... flex duct should be used sparingly. I would not use it for 'the last few feet' as someone else suggested ... just to make it a little easier to connect to the boot. Personal opinion. Most applications you should be able to make a reasonable connection to the boot with all rigid duct.
Seal the duct ... NO DUCT TAPE ... that is ... no classic grey tape ... GREAT for EVERYTHING .... EXCEPT ductwork. Best sealant is probably standard mastic brushed on. Don't know the ins/outs of the pressure sensitive foil tape. I've used it ... it seems good (but so does duct tape when you first put it on).
Most contractors probably won't size ductwork too much is my guess ... which would require a room by room heat loss calc. If you will have access to the ductwork, you might consider air balance dampers (I had them in my turn of the [last] century house). They are 'standard' and can help you balance the system as needed. Particularly good if ducts are sized by rule of thumb. If you sheetrock the duct in, you won't have access ... conider adustable registers to do the same (probably your better choice, but it depends).
Thanks to everybody. This is the kind of information that I was looking for. This is definitely a decision that will last a lifetime and I would rather be asking questions now than wishing I would have asked after the install.
One more question. I had heard at one point that duct board would eventually go bad and have to be replaced. My understanding on this board is that as long as you keep it dry and protected it should hold up well. Is there any reason that duct board would go bad if it is kept dry and protected from any type of abuse?
Thanks again.
The duct board shouldn't 'go bad' ... sounds like a horror flick ... "When Duct Board Goes Bad" ..
The biggest concern I think was keeping it together. I've seen it used in quality commercial applications, but know little about the technology of mechanically putting it together ... i.e. the seams and keeping it that way for decades ... a manufacturer could tell you proper ways of assembly to ensure longevity. If you don't feel comfortable w/ their approach, maybe go back to rigid metal.
Thanks, that was one concern that I had. The last thing I want to do is install something that I will have to reinstall in 10 years.
It's like any trade ... you know the tricks and do it right, it ain't that hard or complex, but if you don't know the tricks (read "the right way"), you can fall on your face. Do it right and you are often 'good to go'. Good luck.
Early on may be 20 years ago their were some issues with duct board. Because of that it got a bad wrap. Today's materials have been around long enough all the problems with the material are gone. Also installers are smarter now in how to use the material. Like I mentioned earlier the concern should be in getting a good installer who will size the system correctly including zoning if he deems it necessary and also has good people doing the work.
It's too bad there's no one in your area that can do the testing. You didn't mention where you are (and it isn't in your profile). If you haven't already, take a look at the Energy Star site and search for a HERS rater (http://www.energystar.gov/index.cfm?fuseaction=new_homes_partners.showHomesSearch).
We're fortunate here in ATL to have a lot of resources, especially Southface.
You're lucky, because it isn't rocket science. It might get you branded as a fussy owner, but I'd ask the installer to put all the ductwork in and seal it up. Then let you look over it before insulating. It'll put the onus on him to not hack it together and hide it with insulation. You might have to look piece by piece, since it'd be a pain to support the stuff, then insulate, then support again.
You're going to look for tape or mastic on every longitudinal seam, at the joints between plenums, ducts, and fittings, and (here's the kicker) on the miter joints of fittings like elbows. And I mentioned before about sealing the duct boots to the drywall- either with caulk, foam or mastic tape (expensive stuff, but I really like it better than standard foil tape). Foam's the messiest but is the most likely to succeed for a retrofit.
I'm throwing this stuff out there because I'm a bit jaded and think that the folks who know to do all this are in a minority of tradespeople (like the ones who are paying attention enough to participate here or at hvac-talk). Oh, and if you haven't noticed I kinda keep operating on the assumption that your ductwork is going in an attic or crawlspace.
We put in a new heat pump system, and our hack GC brought in a hack HVAC contractor. He said, "yeah I install tight ductwork." We had the system sized per ACCA and laid out for him. He set his price with all the testing, rigid ductwork, and sealing criteria in front of him. Then he bitched and moaned about having to actually install the hard duct. When we brought back our designer to test the duct, the system leaked over 1 ton on a 3.5-ton system.
A chunk of that was the boot-to-drywall connections. But there were also lots of unsealed seams and joints, notably a duct-to-plenum connection with a hole about big enough to put your fist through. I demanded he fix the leaks and pay for a re-test, and it all went downhill from there. But that's another story.
I still stand by the design criteria and testing for QA. It's the single largest operating expense for your home and you're going to have to live with it. Unless you're psyched to peel back insulation, look for leaks, and fix them. That's not a fun way to spend your weekends.
Thanks for the info. I am located in Central Pennsylvania. I can't figure out how to update my profile for others to see that. I'm not very computer literate so any help there would also be appreciated.
I'm actually putting the ductwork in my basement. I'm getting ready to finish my basement out and we decided to eliminate the oil furnace and go with a heat pump. Currently we do not have central air and the duct work is not sized properly for a heat pump and central air. It is also not insulated. Therefore it seems cheaper to simply install new ductwork.
I've probably already been branded as a fussy owner because each person that comes to give a bid I've had about 30 or 40 questions for. I have spent 2 hours with them already and I have been talking to people that they have done some work for. I've got it narrowed down to two contractors that I have the best feel about. One wants to use duct board and the other wants to use the steel and some flex pipe. I don't want to regret choosing one over the other so I am trying to get as much information gathered up as possible. I really do appreciate all the help that every body is giving me.
I'm thinking no matter who I go with I will probably take a couple days off work so I can be there to check the duct installs out.
Thanks,
While I have a personal preference of which material I like the truth is all will work. The real issue is to find a competent installer who will design the correct system and have trained people that will install it correctly. All the duct materials have been around for long enough to have had the bugs worked out of them. As with any trade bad installers can make good materials junk. The Energy Star web site evaluates some materials if I remember correctly. I would work overtime to find a good installer. I would get references and call all. I would go to multiple sites your chosen contractor is doing and look at their work. I would get leads on good installers by going to supply houses and asking questions. I am sure there are some builders that have good reputations for doing quality work.near where you live. Go to some of their job sights and see who's name is on the HVAC systems. This is one decision that will have ramifications for a long time. Have I scared you yet? Not meant to. This is what I would and have done myself.
I have worked with 20 year old ductboard systems. There was nothing wrong with the material or foil tape used to assemble the system.
Ductboard has built-in thermal and noise insulating qualities.
That said, I do not like fiberglass ductboard. I believe that some fibers will always enter the airstream even with careful preparation. There are alternatives to fiberglass. I have no experience with those.
Flex has its place, but it should not be used as a substitute for solid ductwork.
Adding to things stated previously in this thread, I would ensure that Manual D is used for proper duct design. In my experience, poor airflow is due to poor installation practices commonly seen in low bid residential work.
I would also make sure that all duct connections are sealed with duct mastic, mastic tape or plain old UL listed aluminum foil tape. Do not use duct tape for anything on ductwork.
Once again thanks for all of the input. It gives me a lot more comfortable feeling to know exactly what I need to be looking for. I believe the two main guys that I am looking at are doing what everybody is recommending but I do have a couple more questions for them after all of your comments.
Thanks for the help.
Adam,I live outside of Philadelphia. There is a HVAC company / metal shop that does design/install. I'm not sure if they would come out your way. More importantly, there is a good video on the website about installing a duct system. They bend there own metal, but they insulate the interior of the duct before closing it up.Good luck, - T(http://www.bobsredtrucks.com/default.aspx)