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 09-03-2011, 10:47 AM   #1
Newbie
 
Join Date: Sep 2011
Posts: 2
Share |
Question

What size main trunk (extended plenum)?


What size do you guys think I should have for my main trunk that will be 20 feet long? 70,000 btu forced hot air, 2ton ac. 8 inches by ? I keep coming up with 8x20, 8x22, and once in a while 8x18. What do you guys think? Thanks in advance.

Heatless is offline   Reply With Quote
Old 09-03-2011, 05:27 PM   #2
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,769
Default

What size main trunk (extended plenum)?


About 8X28

beenthere is offline   Reply With Quote
Old 09-03-2011, 10:06 PM   #3
Newbie
 
Join Date: Aug 2011
Location: Canada
Posts: 7
Default

What size main trunk (extended plenum)?


Sizing you main trunk has many things to think about. Is it a straight run? How many heat runs come off of it? what size are they? etc. assuming you have a 70,000 btu furnace your looking at about 12oo CFM which would be 28x8 duct if straight and only feeding 1 floor.
Tin2Win is offline   Reply With Quote
Old 09-04-2011, 04:31 PM   #4
Newbie
 
Join Date: Sep 2011
Posts: 2
Default

What size main trunk (extended plenum)?


I thought we would figure 400 cfm per ton of ac, 2 ton = 800cfm's that's why I came up with 8x20?
Heatless is offline   Reply With Quote
Old 09-04-2011, 06:04 PM   #5
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,769
Default

What size main trunk (extended plenum)?


Quote:
Originally Posted by Heatless View Post
I thought we would figure 400 cfm per ton of ac, 2 ton = 800cfm's that's why I came up with 8x20?
The duct work isn't sized to the A/C because its A/C. Its sized to the one that needs the most air flow. Which in this case is the heat.

Your furnace needs to move more air for heating then it does for cooling. Or you'll end up tripping on the high limit, having very poor heating, and could even burn out the heat exchanger.
beenthere is offline   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
Doc Holliday (09-04-2011)
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
Add Duct to Main Trunk naturalmystic HVAC 3 11-17-2009 02:25 PM
Sub Panel Main Lug Load Center - Single Phase ? Roy Rowlett Electrical 21 08-20-2009 06:55 PM
Furnace plenum size simonb HVAC 1 01-27-2009 09:09 AM
Main Load center Size Evnldr Electrical 11 06-13-2008 10:10 PM
main lug vs main breaker for sub panel diyll Electrical 1 01-17-2008 08:18 PM




Top of Page | View New Posts

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