Determining Duct Size And Placement - HVAC - Page 2 - DIY Chatroom Home Improvement Forum

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01-28-2009, 11:54 AM   #16

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Yea, as long as your keeping the rooms warm on the second floor 24/7.

If not. Then you must use the temp diff you will have between the floors.

 01-28-2009, 12:28 PM #17 Member   Join Date: Jul 2008 Posts: 233 Rewards Points: 150 i will keep the upstairs warm 24/7, but what do you mean "use the temp diff" how do i do this? also what should i do about the hallway upstairs and the stairs themselves? i was thinking of including that area in the calculation and putting a vent in the wall at the halfway point up the stairs where you turn around to go up the second set. and i was also thinking of putting a return vent at the top of the stairs in the hallway that would connect to another return in the hallway downstairs directly below it, but i wonder if the return vent would suck too much air from the bedrooms (hardwood floors with about an 1" opening under the doors). should i include the halway and stairway in the calculation, and if so, should i put a return up there? thanks for all the help, this is really exciting to me learning how to do these calculations.
 01-28-2009, 12:51 PM #18 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,599 Rewards Points: 8,184 The temp diff, would only be if you intend to keep the second floor a different temp then the first floor. Its a code violation to have a return cavity serve both the second and first floor. They MUST be seperate cavities. Its a fire code. The heat will rise to the upper hallway from the first floorby itself, and the cold air will come down from the second floor hallway by itself. No need to put a supply there. A return would lessen some of the cold air coming down while the system runs. But, other then that, it may not help much during the day while the bedroom doors are open. . During the night a return will help the hallway not to get too warm when the bedroom doors are closed. But its not really required in most applications. The second floor hallway doesn't get included in the first floor calc. The stairway, gets included, as far as its area that is part of the first floor.

01-28-2009, 01:11 PM   #19
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very helpfull. thank you

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