Being across the border here in WI, we typically don't work if it is under 15 degrees or so. That is for window replacement, siding, etc where materials become brittle, caulks can have difficulty adhering properly, etc. That said, 1) that is just our preference, as there is no hard rule, and 2) if they are replacing sashes only and not doing any carpentry, caulking, etc, I'd have no qualms about doing that @ 0 degrees.

Thanks a lot.
The new sashes need to be stained to match color of the frame. Installer told me that they will do it after installation. I understand it can be done for the fixed panel, but what about casement windows. Don't they need to open them to stain all over and keep open until it dries out? How does it work in the winter.

Because of your situation, I would ask that they stain them before they are installed. What could happen though is you may lose the opportunity to have them installed now and may have to wait further.

I'd also prefer them to be stained BEFORE installation. Then only touch-ups ---if anything---are needed after install. That is standard procedure in my area.

Thanks for the advices, this forum rocks!
Are there windows installers in Minneapolis area who could be interested in this project? I am really disappointed with my contractor and would like to work with another one
Thanks