Air moving up through a house often follows the plumbing or electrical lines and slips through the penetrations where they pass through the walls, cabinets, and floors.
The best way to close off these exits is to follow the lines yourself and seal around the penetrations with non-expanding insulating foam.
For plumbing, follow both the supply and the waste lines. Check in cabinets, under floors, and in the attic.
Seal around exterior vents from bathrooms or kitchen exhaust fans with silicone caulk.
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