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Old 12-11-08, 11:41 AM   #3
Efficency nerd
Join Date: Dec 2008
Location: S. E. Michigan
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You should seal up your ducts with either furnace mastic or AL tape. I did this when I was was remodeling my basement, and it made a big difference in how much air comes out the longest runs. Make sure that the heating vents in the basment are not just off, but covered with cardboard / AL tape. The vents right next to the furnace see the highest pressure an vent the most.

There is a balance between installing fast and making a good seal, guess which way the contractors want to go? FAST INSTALL. I have read that each junction will leak about 5% of the air in it to the outside, and how many junctions are there? 25? 50? More in a big house. In general, an unimproved duct system will lose about 35-50% of the air through the leaks. Joist return ducts are the worst though. All are easy to fix with the above materials, just DONT use any fiber backed tape, like duct tape!!
Also, cleaning you blower fan blades can make a bid difference in how much air it will blow. They usually never get cleaned.
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