New addition went on this spring, and ever since then the two far bedrooms feel like a different climate zone—cool in the morning, stuffy by late afternoon. The contractor added a couple of flex branches off the main trunk, and now I’m second-guessing whether leaks at takeoffs or boots are sabotaging airflow. Static pressure at the furnace seems a little high (filter change didn’t help). Before I call the installer back, what’s the smartest order of operations for a homeowner: leak sealing first, then balancing, or the other way around?
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The biggest surprise there was the gap around the supply boots—looked harmless, but smoke showed air rushing through. After mastic and a bead of painter’s caulk at the drywall, the thermostat swings calmed down a lot. Planning to go over the plenum seams next and will study that guide before tinkering with dampers so I’m not compensating for leaks with balance settings.
Given those symptoms, start with sealing, because balancing a leaky system just masks the problem. Focus on the metal plenum seams, takeoff collars, flex-to-collar connections (tighten the drawbands), and the supply/return boots where they meet drywall—air loves those gaps. Clean joints, press mastic into seams with a chip brush, and back it up with UL-181 foil tape on long straight seams. Avoid cloth tape; it dries out and fails. Don’t forget the cabinet itself: many air handlers leak at panel seams and the filter door. A concise walkthrough of why this saves energy and improves comfort—plus the common leak locations—is here: https://www.iplocation.net/duct-sealing-the-hidden-energy-saver midway through your planning, then come back and set manual dampers ¼-turn at a time to trim room temps. If you have fuel-burning appliances nearby, crack a window while testing to avoid backdrafts, and consider a pro pressure test if comfort still swings after sealing.