Replies

1. 
   agurkas | Feb 18, 2016 11:53am | #1

   Also, this is how close the branches are to the band joist. They aren't insulated, so joist is nice and toasty each winter.

   
2. GBA Editor
   Martin Holladay | Feb 19, 2016 08:24am | #2

   Apollo,
   I doubt if it's possible to provide you with a new duct system design (or a short course in sheet metal work) in our Q&A column.

   Here's my advice:

   1. A good duct design requires a room-by-room heat loss and cooling load calculation. In most cases, this is done using the the Manual J method.

   2. A good duct design is performed using the Manual D method. Manual D requires inputs from Manual J.

   3. If you don't have the software and knowledge to perform Manual J and Manual D calculations, you should probably hire an energy consultant or mechanical engineer to help you.

   4. For an overview of duct design issues, see All About Furnaces and Duct Systems.

3. 
   agurkas | Feb 19, 2016 08:36am | #3

   Martin,
   There is no room-by-room issue, because this system serves only one - living room with cathedral ceilings and kitchen attached to it. This is single zone, 98% efficiency furnace. We did manual J for it, hence the sizing of it.

   Sizes of vents won't change, size of the system won't change either, so it is just a matter of do I do one T shape trunk to match 1K CFM and split into equal 500CFM sub-trunks after which three takeoffs of equal (?) size come off it and go to individual register.

   Or I go with U shaped trunk and just replicate current setup except for now each register will have flex duct (or bunch of elbows) going from saddle taps to the vent boots.

4. GBA Editor
   Martin Holladay | Feb 19, 2016 08:52am | #4

   Apollo,
   I tried my best, but I can't understand your descriptions of your two options.

   If you make two sketches -- one showing Option 1, and the other showing Option 2 -- then GBA readers will be better able to provide you advice.

5. 
   agurkas | Feb 19, 2016 09:37am | #5

   Actually articles linked from your article were very helpful. I need to think about matching TLE on both branches

   My challenge is that 7' from the furnace there is a 12" ibeam with sistered joists above, so I have only 9X11 cavities to work with. Floor joists are going convenient direction for the trunk, but not for the branches.

   There has to be online duct layout Manual D software. No? Or is the HVAC world still stuck in the 90s with Windows only software?

6. GBA Editor
   Martin Holladay | Feb 19, 2016 09:55am | #6

   Apollo,
   You can order Manual D software online. Here are some links:
   http://www.elitesoft.com/web/hvacr/elite_manualdductsize_info.html

   http://www.adteksoft.com/software.html

   http://www.wrightsoft.com/Products/Right-Suite_Universal

   Not everything in life is free, however. Software developers have to pay the bills (just like journalists and editors).

7. GBA Editor
   Martin Holladay | Feb 19, 2016 10:03am | #7

   OK. If you locate good, free, open-source software for residential duct design, please post a link here.

8. 
   agurkas | Feb 19, 2016 10:03am | #8

   Martin,
   I run software development company, I know about free stuff - it is called opensource :-)

   Thanks for the links. Prices seem reasonable, so I might grab one. I have picked up finance in under a year, so learning Manual D isn't exactly rocket science to me.

9. 
   agurkas | Feb 19, 2016 10:11am | #9

   I have seen around also duct design services that seem to be reasonably priced under $300. That may make sense too. Or I can just replace the nasty ducts with same or next size over ones and just shorten trunks by one joist bay