Home Improvement, Remodeling and Repair @ Builders Websource. Home design software, advice, tools, videos, tech notes, links and more!

Search: 

Home Page | Books | BuildersTALK | Building a Dream | Green Building | Links | Software | Tech Notes | Tools | Contact

Messages and Online Forum Q&A

If you find the answer to this question useful, kindly CLICK TO PAY here.



Knowledge


BuildersTALK
Building|Dream
Green Building
How-To Books
Links (Web)
Newsletter
Tech Notes
Videos

Software


BeamChek
Bidding
CAD | AutoCAD
Estimating
EZHomeBuild
Home Design
Landscaping
Lighting Design
PrioSoft
Resi-Cost
Structural

Specialty Tools


CrackMON
Tools
WatrLevel

Support & Info


About Us
Advertise
Contact Us
FAQ
Publish
Services
Support

 

Re: Adding additional air ducts in unfinished basement

From: info@builderswebsource.com
Category: HVAC
Remote Name: 63.198.181.43
Date: 29 Sep 2001
Time: 12:06 AM

Comments

Your general method sounds correct. Be sure to use duct tape to secure all joints and prevent air leakage. Builders Websource prefers the use of flexible insulated aluminum ducting. The aluminum helps to keep fiberglass insulation from blowing through the ducts...and the metal is more durable. The only drawback of metal ducts is their higher materials cost and that they can get squashed if you're not careful...and once they're deformed, it's tricky to restore them to their original shape.

As a rule of thumb, each vent outlet should be fed by approximately a 6" round duct, depending on the size of the room. Larger rooms may require two 6" ducts or more. The rule of thumb is to work backwards from each vent location to determine the maximum diameter feeder needed. For example, a 6" round duct has an area of 28 square inches. Therefore, if you have two 6" ducts, you need 1 wye that has an 8" input and two 6" outputs. The reason for the 8" input is that the combined area of two 6" ducts is approximately 2*28, or 56 square inches. An 8" duct is about 50 square inches, so this is an acceptable match. Adding a third 6" duct to the 8" duct, would require a 10" inlet. That's because a 10" duct has approximately 78 square inches, or about the equivalent area of three 6" ducts. You can see that the pattern is roughly for each 6" duct you add, the supply trunk expands by 2" in diameter. This formula holds true typically for supply trunks in the 14-16" range, give or take.

Now, be sure that your return air duct is at least as big as your supply duct, otherwise the air flow will be unbalanced. Some installers use dampers inside the wyes in order to fine-tune the air balance for each room.

Determining how many air ducts you need in each room requires a BTU calculation based on the thermal loss of the structure and volume of air in each conditioned space. But assuming you follow the rule of thumb above, and assuming your heater can support the added capacity without damage to the furnace, then you'll be in the ball park.

Builders Websource

 

Article Tools

BuildersTALK


Ask an Expert
Recent Questions
Click to Pay

Archives


2006-2007
Oct-Dec 2002
Jul-Sep 2002
Jan-Jun 2002
Jul-Dec 2001
Jan-Jun 2001
1999-2000

 

 


ASTM International