View Full Version : How restrictive..?
03-23-2010, 10:30 PM
In general, how restrictive are horizontal offsets when needed in a return air drop? For instance, you have a straight vertical 14x20 return drop, but it would have to be moved over 6 or 7 inches to the left to compensate for newer equipment.
See attachment below for an idea of what I'm talking about (6-7" offset to left). I am trying to somewhat design or plan out the installation so that it goes smooth. Easier to plan necessary changes ahead than have to worry about them during the install. I have been in contact with the local pros I will be working with.
03-23-2010, 10:52 PM
The offset you have drawn isn't the biggest problem, but less is better. Having 90s stacked consecutively is much worse, especially when going in opposite directions - S pattern. Create as much space as possible between 90s.You may want to try to relocate the air filter to a straight length of duct to optimize uniform air flow/effectiveness.
I believe you were asking about HP's last week? HP's are not tolerant of friction/restriction issues so... do a good job. The contractor you use will agree, and have many other good/better ideas.
03-23-2010, 10:54 PM
Rather than build offsets to install a media filter, is there a way to transition the drop duct to put the filter cabinet in horizontally?
03-23-2010, 10:58 PM
Btuhack, I agree that the HVAC manager will likely have further suggestions to minimize air resistance and transitions. Thanks for your thoughts.
Flyers, the cabinet (or electronic air cleaner) could be installed horizontally in the drop. However, there will also be a humidifier as well as a 6" return run to that drop for the basement. When we finished the basement, the crew cut a return right in the upstairs return trunk line--not the best idea, because now the upstairs gets little airflow through that return. So the 6" is a new return for the basement with the existing removed.
All input is welcome and appreciated. Many thanks.
Think outside the box!
Hope you can follow this.Can't scan a sketch in from home.
Install the air filter/cleaner horizontialy in the 14X20 drop, transition the 14X20 gently to the filter,then after the filter gently back to the opening size of the furnace before the 90/elbow,but turning vanes in the 90/elbow that goes into the furnace.
PD testing of filter is with 3 feet of straight duct,to prevent turbulence,best to install them that way,to keep th PD lower.Vanes in the 90/elbow,further minimize the PD/Static.
03-23-2010, 11:10 PM
Installing the filter horizontally would eliminate then need for the offset, so that seems to be the way most are suggesting here. Goal is to put the filter low enough so that there is room for a 6" return and a humidifier. Shouldn't be too big of a problem. I'll discuss with installers in the future and possibly post another sketch tomorrow if I have time. Thanks for your comments dash--you seem to be the pressure/static/duct expert here and your experience is valued.
03-23-2010, 11:12 PM
measure your pressure drops, if it's too much add turning vanes
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