Window Fitters Guide to Window Installation 
13               ©2022 AWDI, LLC Do not reproduce without permission
Figure 3:
Modern Replacement
Windows have tighter
tolerances in the
weatherstripping and 
at the interlocks. 
This better design 
and construction 
cures most of the 
window caused air 
and heat transfers
because the gaps 
have been closed.
Figure 1:
Most older windows
were installed when
energy costs were lower
and building codes
were not so stringent.
Air could come into the
home and heat could
escape through joints
in the window frame
and the rough  framing
and siding and wall
board. 
Also leaking air and
heat are the joints
between the sash and
the window frame and
the interlock of the
sash. Even well weath-
erstripped windows
wear out eventually.
Fig 1
Fig 2
Fig 3
Fig 4
Figure 2:
Adding to the air leak and heat escape is the lack of 
insulation in the interior pockets. There are pockets of
empty space where the old weights and balances were 
hidden, and between the tapered sill and the flat rough
sill, and above the window header — as well as the side
jamb cavities.
Thermal imaging
shows the heat loss
through the window
and through the frame
around the window.
Figure 4:
Too often the new window is fit to the left-in-place old 
window frame without insulation in the weight/balance
pockets, below the sill and above the header - or in the
jamb cavities. This leaves
significant drafts, heat loss
and dissatisfaction with the
performance of the new
windows. Thermal images
show the cold around the
new window even though
the window itself is
“warmer”.
Before Replacement
After Replacement
SAMPLE MANUAL

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