Interesting take, but I’d argue the glass itself makes a bigger difference than you might think—especially if you went from single-pane to double or triple. Sealing gaps is huge for drafts, sure, but modern windows have low-e coatings and better thermal breaks that cut heat loss even more. I’ve pulled out some wild “insulation” too (old socks, newspapers), but nothing beats proper foam or mineral wool for air sealing. Noticed any condensation issues since the swap? Sometimes tighter windows mean less airflow and more humidity inside...
Pulled out a window from a 1960s ranch last winter and found a whole time capsule in the cavity—old comic strips, a couple of socks (one with a hole the size of a golf ball), and what looked like petrified pink fiberglass. Guess that was someone’s idea of “insulation” back then. Can’t say it did much, judging by the drafts.
You’re right about the glass making a big difference though. I used to think all the magic was in sealing up gaps and cracks, but once you swap out single-pane for double or triple with those low-e coatings, it’s night and day. The thermal break in modern frames helps too, especially if you’re in a climate with real winters. I’ve had clients call me after the first cold snap saying their furnace barely kicks on anymore.
Funny thing is, after tightening everything up, some folks notice condensation on the inside for the first time. It throws them off, since they expect new windows to solve every problem. But like you said, less airflow means humidity can build up indoors—especially if people are cooking more or drying laundry inside during winter. I usually recommend running bath fans longer or even cracking open a window now and then (feels counterintuitive after spending all that cash on new ones, but sometimes you gotta).
Mineral wool’s my go-to for air sealing too—never trusted newspaper to do much besides confuse future renovators. Spray foam’s good but can get messy if you’re not careful.
Biggest surprise for me was how much debris collects in old sills... dead bugs, bits of insulation, and once even an ancient Monopoly piece wedged behind the trim. Makes you wonder what else is hiding in those walls after 50+ years.
Anyone else ever find something weird stuffed around their old windows?
Funny thing is, after tightening everything up, some folks notice condensation on the inside for the first time.
I get what you’re saying about condensation, but I’ve actually found it’s not always a humidity issue. Sometimes it’s just that the new windows are so much colder than the room air (especially if they’re not installed perfectly plumb or insulated around the frame). I had a bay window swapped out and even with fans running, there was still fogging in the corners. Ended up tracing it to a tiny gap in the spray foam—so sometimes it’s less about airflow and more about those hidden leaks. Just goes to show, even with all the right materials, installation can trip you up.