The problem: Heating and cooling ducts that aren't well sealed; ducts can leak as much as 30%, says Sam Rashkin of the Department of Energy's Building Technologies Program.
The solution: Try Aeroseal, a process in which technicians blow sealant into ducts, filling cracks from the inside. It costs about $1,500, but could slice half that sum off annual utility bills.
For a cheaper option, DIYers can cover accessible ducts with less than $100 worth of metal tape or mastic sealant.
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