Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 10-29-2011, 11:23 PM   #16
Member
 
Join Date: Oct 2011
Posts: 68
Rewards Points: 75
Default

Ductwork sizing help


Read this, start with section 28.5.1 this will get you ballpark numbers very quickly

http://www.alpinehomeair.com/related/Ductwork.pdf

The manual X,Y,Z books give you over precisely incorrect results to the 12th decimal place. (Because there are so many inputs to the equation, most of which are approximates or unknown.)

The supply side needs more attention then the return, the return can never be too big, but should at least be bigger then the supply side (carry more cfm). The supply size can be too big or too little, but it's better to be too big.

Figure out what each room needs according to the tables in ductwork.pdf, then work backwards, make sure each trunk line is big enough to supply all the branches off it. It helps to reduce the trunk size just after a branch is taken, this will keep the pressure constant for the next branch down the line.

The branches/takeoffs/elbows are where all the resistance is, make them as smooth as possible, read this

http://www.perfect-home-hvac-design....-fittings.html

if you are forced to use a bad branch or multiple wacky elbows, make the duct one or two sizes larger then the calculations show, this will reduce the resistance.

Plenum takeoffs should be at least 30 inches from the bottom of the plenum, but at least 6 inches below the top of the plenum.

Most people make the ductwork too small, mainly to save space.

Good luck!!!!


Last edited by bungalow_steve; 10-29-2011 at 11:45 PM.
bungalow_steve is offline   Reply With Quote
Old 10-29-2011, 11:45 PM   #17
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,981
Rewards Points: 3,632
Default

Ductwork sizing help


That PDF under sizes all the duct work.
beenthere is offline   Reply With Quote
Old 10-31-2011, 09:23 AM   #18
Member
 
Join Date: Oct 2011
Posts: 68
Rewards Points: 75
Default

Ductwork sizing help


Quote:
Originally Posted by beenthere View Post
That PDF under sizes all the duct work.
Maybe for a hack job (bullhead tees, no turning vanes, long branches >25 feet, flex duct) but for a pro job with low TEL they are industry standard proven. As I said in my post, increase the size by one or two if you can't do it right.
bungalow_steve is offline   Reply With Quote
Old 10-31-2011, 05:13 PM   #19
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,981
Rewards Points: 3,632
Default

Ductwork sizing help


Quote:
Originally Posted by bungalow_steve View Post
Maybe for a hack job (bullhead tees, no turning vanes, long branches >25 feet, flex duct) but for a pro job with low TEL they are industry standard proven. As I said in my post, increase the size by one or two if you can't do it right.
They are industry short cut standard, not proper.

I've measured the static on many of those "short" run jobs. And they are always higher then .5" TESP. And thats sheet metal and hard pipe jobs.

The average supply run is more then 40' of TEL. And thats not including a PD for the register, or a balancing damper.

beenthere is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Adding new ductwork to a second floor. vr4Legacy HVAC 4 01-27-2011 11:51 AM
Ductwork Insulation tk3000 HVAC 3 11-19-2010 05:08 PM
Sizing and installing Ductwork. 50juan HVAC 30 07-09-2010 10:25 PM
plastic ductwork vs. metal: acoustic duct liners jjpclev HVAC 5 02-26-2010 08:29 PM
Moving ductwork to accomodate finished basement Badfish740 HVAC 1 01-13-2010 04:11 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.