Repair broken sash cords or...?

In my bedroom, all 5 double-hung windows have broken sash cords on the window counterweights. I was going to replace the cords, but when I took the windows apart, I realized that those empty uninsulated cavities on 5 windows are a huge heat loss. So now I'd like to stuff the cavities with insulation. If I do this, is there another way to make the windows work correctly (stay open)?
Thanks in advance,
Jeff
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There are some retro-fit kits than can be used. I have never used them.
Colbyt
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Jeffrey Hersk wrote:

I would replace them. Those open areas are not that big a energy loss if they are properly sealed. Far less than you will lose through the window.
It is hard to beat a good basic window for service.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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I would like to add to my earlier post, posted as the dinner bell rang. I agree with Joseph.
What I did in a similar situation was convert the double hung to single hung and caulk all the cracks inside the weight cavity and the upper sash both inside and out. Most of them have long since been painted shut in the closed position anyway.
Colbyt
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makes them easier to open and close RayJ
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Jeffrey Hersk wrote:

The usual modern revamp is to convert the sash to friction channels. The cavities should be thoroughly filled with an approved insulating material, then covered and sealed.
(Many 19th century windows of this type were not originally built with sash cords -- if you have them they may be a 20th century retrofit. The sash would have a button lock that would hold it in place in two or three positions.)
Balance this with the preference by some old-house buyers for original sash equipment. You can buy insulating covers that reduce the air flow over the top of the sash cord pulley. Ultimately, although the cavity has an effect, you should be more concerned with making sure the entire window frame is properly caulked inside and out. It's air *flow* that you need to worry about, and the innards of old window frames are full of nooks and crannies that can let a minuscule draft through. If you solve that the cavity is a null space the same as a double-glazed window.
Although I love old-fashioned windows myself, they require storm windows, and my experience with the aluminum storm windows commonly used, at least in a lot of extant buildings, has not been positive: warping, drafts, impossible finger grips, etc. Just today I was dealing with one of them whose weatherstripping is shot and whose parts no longer fit together reasonably well.
What I'd really like is a way to use the original sash in a retrofit that would resemble modern tilt-in vinyl windows, i.e. with all the ease of use features but retaining as much of the original architectural charm as possible.
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imho if you're worried about the lost heat, the place to start is with the windows themselves... im guessing since they use cords they are single pane. replacing them with modern windows without the weights will solve everything.
randy

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