Supply Line Planning
#1
03-05-17, 04:33 PM
Join Date: Mar 2017
Location: United States
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Supply Line Planning
Hi, so I'm finishing a bonus room and the builder supplied a 6 in supply line that has to registers in series. After doing the math I actually need 2.8 registers based on 80 CFM flow for a 6 in line but I'm pretty sure it's not as easy as tapping into the last register on the current line and adding two more.
Anyway, I may be committing a huge crime assuming a 6 in duct will supply 80 cfm but that's what I'm running with right now and the attached diagram shows the current situation and where I need the new ducts.
The question is do I need to tap into the main supply and run more 6 in duct, or can I run them in series? Any details you feel like adding will be helpful. My most recent quote for this work (no dry wall or insulation in this area) is 1700 for flex duct, seems to me like he's telling me to DIY.
Anyway, I may be committing a huge crime assuming a 6 in duct will supply 80 cfm but that's what I'm running with right now and the attached diagram shows the current situation and where I need the new ducts.
The question is do I need to tap into the main supply and run more 6 in duct, or can I run them in series? Any details you feel like adding will be helpful. My most recent quote for this work (no dry wall or insulation in this area) is 1700 for flex duct, seems to me like he's telling me to DIY.
#2
03-05-17, 04:56 PM
Group Moderator
Welcome to the forums.
I'm not an installer.... just a servicer but..................
You are asking us for a guess.
You didn't leave any room measurements.
75cfm is usually max. for a 6" flex duct. It doesn't mean yours is putting out 75cfm.
I'm not an installer.... just a servicer but..................
You are asking us for a guess.
You didn't leave any room measurements.
75cfm is usually max. for a 6" flex duct. It doesn't mean yours is putting out 75cfm.
#3
03-05-17, 05:06 PM
Super Moderator
There really isn't enough info to be able to help you.
The duct's ability to carry volume depends on how much air and pressure is available in the plenum and what velocity you are prepared to live with. (more velocity, more noise).
Without knowing more you likely should run 6 inch back to the furnace and put a balance damper in the line.
The duct's ability to carry volume depends on how much air and pressure is available in the plenum and what velocity you are prepared to live with. (more velocity, more noise).
Without knowing more you likely should run 6 inch back to the furnace and put a balance damper in the line.
#4
03-05-17, 06:26 PM
Join Date: Mar 2017
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Info
Ignore the large hallway to the right of the main room with one register in it. I will be putting a wall across there. When thats done the measurement will be 12.5 ft by 20.5ft. Knee walls are at about 5 ft and peak is 9 ft.
The duct will be at the peak already, so to put something larger then 6 in in I would have to adjust the framing they did to allow for it to travel between the peak of the house and peak of the room. Would it work if I do as the picture shows and just tap off the current supply line and add two more ducts to the room? What other information would you need to give better advice? How can I find out the pressure at the plenum?
The duct will be at the peak already, so to put something larger then 6 in in I would have to adjust the framing they did to allow for it to travel between the peak of the house and peak of the room. Would it work if I do as the picture shows and just tap off the current supply line and add two more ducts to the room? What other information would you need to give better advice? How can I find out the pressure at the plenum?
#5
03-07-17, 04:55 AM
Member
Your original duct if 6in metal duct can handle 100 cfm at .08 friction now you are going to tap off of it and add 2 more 6 in ducts. So your max you could get out of each register is now 33 cfm best case.
#6
03-07-17, 05:00 AM
Member
With out all the info you will need about 250 cfm in this area. Remember you are also taking that air away from the rest of the house. Thats a bit more than a half ton of cooling you will not have for the existing home. Have you looked into a 9,000BTU ductless split heat pump?
