Brand new replacement windows leak cold air!

6 Jan 2013
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United Kingdom
We recently replaced all of our leaky Double Hung windows with "Renewal by Andersen" Double Hung.

The installers removed the old sashes and stops and inserted the replacement unit in the hole, and centered the window unit in the opening. I saw them plumb & shim the sides of the window directly behind the pre-drilled screw holes in the jamb. (actually they didn't use the middle screw hole.)

The team was being very frugal with the foam insulation between the units frame and rough opening, they only insulated the top and sides, leaving the area between the sill and the bottom of the replacement window totally open. Once they completed the installation; the only thing blocking the air flow underneath is the outside metal flashing and the wooden Stool on the inside.

I was very concerned by the incomplete foaming job but they assured me that they HAD to do it that way to prevent condensation. In their own literature it mentions improper installation can occur if the installer does not insulate fully between the window and the rough opening!

Now that it is below freezing our house is cold and drafty. Tonight its 32 degrees outside and using my infrared thermometer the walls and frame around the middle of the window is 64 degrees... But the window Stool measures 50 degrees. Some windows are even colder, you can feel a draft, I've even held a lit candle close to the window seams and the flame bent at the draft.

Is it ever correct to leave the entire bottom uninsulated?
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