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There seems to be a lack of published material on doing duct work. I am in the midst of a home-owner bathroom remodel and am moving some ducts. I need a reference to what is and isn’t kosher. There are books about electrical work, plumbing work, tile work. Why can’t I find a book about duct work? Is it too simple to write a book about? My efforts so far seem to indicate that I need help. Can anyone recommend a book?
Thanks,
Ski Dad. . .
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Replies
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I would agree that there isn't a lot of DIY literature on ductwork. Perhaps because far fewer people take it on themselves or maybe because there are so many more variables. Electrical outlets are always 120 or 208-240 volt and of some easily defined amperage, but the flow of hot air varies by volume (cfm), allowable pressure drop (inches water column), run length, and temperature. And all those things are inter-related.
For electrical circuits, one could say, "Run 12 gauge to all 120 volt outlets." But for ductwork, anything from 3" to 8" round or various rectangular size might be the right answer.
I see two approaches. Learn the theory from ASHREA publications or a good ChemEng or MechEng cirriculum and then practice doing the calculations. Or learn the rules of thumb and accepted practice that HVAC tradespeople use.
Since you are replacing existing ductwork, you've got an easier task. Assuming that heat distribution was well balanced before, just duplicate what was there. Maintain cross-sectional area in each run. If you make a run longer, go up a size in the ductwork. Minimize bends - they add a LOT of pressure drop. Adding a new room to the system will require larger ductwork to that area of the house or a booster fan for that leg, unless that area was a little too hot to begin with. Anyone know of a good book or publication for SkiDad? -David
*I had the same problem since the ductwork in my 18 year old house was poorly installed.What you need is a copy of the ACCA (Air Conditioning Contractors of America) Manual D, which covers systems & applications, blowers & air-side devices, Sizing Calculations and efficiency, leakage & noise.ACCA's national HQ is Washington DC. Their number is 888-290-2220, web address is http://www.acca.org.You may have an ACCA chapter in your town that has the various manuals and a catalog. Call ACCA and ask them.I plan on redesigning, removing the old and installing a new duct system in my house before the Texas heat sets in. Good luck
*There was a thread like this a while back, with discussions on equal friction, static gain, etc. The best practical advise was to follow Dave's advise on bends and install the biggest ducts that will fit (with appropriate dampers) physically and aesthetically and forget any calcualtions. Adjust the dampers to suit your lifestyle and room usage after completion.
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There seems to be a lack of published material on doing duct work. I am in the midst of a home-owner bathroom remodel and am moving some ducts. I need a reference to what is and isn't kosher. There are books about electrical work, plumbing work, tile work. Why can't I find a book about duct work? Is it too simple to write a book about? My efforts so far seem to indicate that I need help. Can anyone recommend a book?
Thanks,
Ski Dad. . .