Just had a eureka Moment!
I remember seeing it in an old house. You take those copper weather strips and fold them over, so you have an upside down V.
Then it goes where the two pieces of the double hung windows meet. When you close them the 'V' compresses, leading to a airtight seal!
Same goes for the top and bottom. The way they did things 140 years ago, with the tools they had, was just genius.
<click>
That's it!
The guy before me used clear silicone caulk on ALL the windows to achieve this seal. The copper strips must have been taken out of the windows for the copper value at one time.
Caulking 140 year old windows shut!
The previous owner must work for Lowes.
OK, I'm going to need A LOT of this stuff.
(8 foot windows, both sides, top, middle = 28 ft per window
11 windows first floor, 16 windows second floor, 6 windows top floor
33 windows time 28 ft = 924 linear feet!)
I hope this stuff isnt too expensive.