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Self Installation of A/C Ducts?

Jgriff | Posted in Energy, Heating & Insulation on August 3, 2002 10:20am

Don’t work with HVAC as a rule except when I have to get around it.  But now the wife has convinced me to install central air.  2 story colonial so there’ll be a fair amount of construction just for the vertical runs. Already have oil heat with baseboard so that probably won’t factor into the mix.

I’d like to explore how the ducting is done with an eye to seeing if it’s something I can tackle to save some labor. I’ll leave the actual placement and connection of the ac unit to the pros, but the carpentry and joinery of the ducting seems like it should be within my capability. Just saw a re-run of This Old House from several years ago with Rich Trethewey exhibiting rectangular interlocking (modular?) insulated ducting (not metal) and hand tools to connect the circular branch ducts to the rooms. I mean, this can’t be that difficult…..can it?

Anyone able to point out a good book, or a couple of them, or some other source to act as reference material to learn about this? Thanks.

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  1. ahneedhelp | Aug 04, 2002 01:00am | #1

    If you're going to tackle the ductwork yourself and hire a contractor for the mechanical stuff, talk to the contractor about duct sizing, both for the trunk and branch lines as well as the returns.

    The contractor may not want to sell you only the mechanicals if the configuration of the ductwork is not compatible with what he thinks is the proper tonnage for the house.

    We got central A/C in our brick ranch two years ago and running the ductwork in the attic is a lot easier in a single story ranch then what you're looking into. But I gladly let them take care of the whole thing. The job was done with no mess and dust after cutting numerous holes into the plaster ceiling. Except for some scuff marks on the wall next to the attic access, they did not leave a trace.

    And the properly sized and configured system runs nearly silently dispite the air handler being in the attic.

    I am quite the DIY fool myself but I drew the line on this one.

    And your wife may appreciate it if you didn't turn it into a lengthy project, which definitely will take a lot longer then if the pros breezed through it. This, ofcourse, depends on who you choose to do the work.

    Alan

    1. kpb | Aug 04, 2002 05:05pm | #2

      I can't tell from your message what part of the country you live. A two story HVAC installation is more complicated than you may think. So I would also leave it to the "pros". However, many experienced(think older) HVAC guys hate to do installations. So they let the new guys (think younger less experienced) do the installs. Sometimes the results are less than desireable in terms of noise, comfort, air distributions, balanced systems, etc. I would ask around about dealers. Remember straight runs are best and adequate return flow is as important as supply.

      kpb

  2. NPitz | Aug 04, 2002 06:00pm | #3

    Having installed central air in my own house, and doing a fair amount of ductwork installation, I can tell you it's not as easy as it looks. My HVAC sub is a 76 year old HVAC guy who has forgotten more than most people ever know. He isn't up to doing installations anymore, so I do the ductwork, and he hooks up the system. There are a lot of subtleties to working with ducts that you don't realize until you watch someone who really knows what they are doing. And once you're done, and you hook it up, if it doesn't work right, it is hard to fix.

    Anyway, at a minimum you have to find somebody who can help you size everything. A good HVAC supply may have somebody who can give you advice. Or maybe you can pay someone to come in, tell you what sizes to put in, and where. At a minimum, look for something that looks like a slide rule called an Air Duct Calculator, that gives you equivalent sizes and flow rates. Stay away from long runs of flex duct, and too may elbows or direction changes.

    1. ahneedhelp | Aug 04, 2002 06:50pm | #4

      Chiming in on comments about who does the actual work, I was very fortunate to end up with a 2-dude team who did an excellent job without making a mess out of the plaster ceilings.

      On the otherhand, my friend had problems with a guy who had teamed up with one of the guys on "my" team and was messing up the plaster ceilings with sloppy cuts. He had to demand the guy be taken off the cutting tasks.

      Yes, even with the most reputable company in your area, there's always that chance of ending up with a bonehead that does the grunt work but is no less critical in the job's finished appearance.

      As for the DIY attempt, how are you going to buy the duct material ?

      The registers ? etc.

      The ceiling registers that are installed in our house work so well that there is no noticeable breeze when the A/C runs.

      In fact, we have paper wind socks our kids' make taped near them to get a visual clue.

      Alan

  3. Piffin | Aug 04, 2002 08:37pm | #5

    I've never seen duct install itself, LOL

    But I think that you've got the right approach here, Get some books and study them first. By the time you are done with that, it'll be winter and she'll have forgotten about the hunnydue project. Think of the money that'll have saved.

    Excellence is its own reward!
  4. TLRice | Aug 06, 2002 03:24pm | #6

    Griff,

    If you really want to DIY, the best source for materials and components that I know of is GW Berkheimer (www.gwberkheimer.com). They sell almost every standard off-the-shelf duct and fitting you would need. Get a catalog, layout your system IN DETAIL. Determine every bend, take-off, offset adapter that you will need. Keep the flex limited to no more than 5 feet and don't use anything smaller than 6". You can do an entire system from the cataolg, but you will have to plan it well. People who do this for a living typically have to custom fabricate transitions and offsets and are in constant contact with the shop. Fabricating any piece of ductwork is a specialty, not DIY by any menas.

    Get a ductulator and size the duct to no greater than 0.08" per 100' for friction, 0.05" is better and nno more than 1000 fpm velocity. Do you know how big the system is to be? Have you done load calculations to determine the size of the unit and how much air you need in each room?

    BTW, I designed the system that's in my house, but I paid professionals to install it. I saved on the installation by doing all the dirty work, cutting the holes and cleaning up after they left every day. It took a two man crew 5 days, with my limited "help". 2 floors and a basement, 4200sf, 4 ton ACCU/coil, (I had the furnace) cost $8500 including relocation of the furnace, all material, AC, electrical work, and a power humidifier.

    If you still plan on DIY, good luck!

    1. Jgriff | Aug 06, 2002 07:02pm | #7

      Thanks everyone for your knowlegeable replys.   All have helped convince me that this is not a job I want to attempt.  Breaks my heart that I have to tell the wife.

      Wonder what project she'll think up next for me?  Maybe a jacuzzi on wheeled track so she can have it motored inside during inclement weather.

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