exterior temperatures, and can condense on the cold-
er outer surfaces of the window and especially the
aluminum capping. This condensate, if trapped, can
cause mold, mildew and rotting within the cavity.  An
installation that breathes allows evaporation of the
moisture-laden air reducing the chance of this dam-
aging condensation.
There are other advantages to this method. Old 
pulley holes, the space vacated by the parting stops,
and other problems are covered by the F Channel.
The insulation, often used in the cavity, now fills the
space between the window frame and the F-Channel.
The F-Channel, when installed, can be anchored
using a sealer caulk, and (if necessary) large head
roofing nails to hold it in place. The F-Channel on 
the sides of the opening should be notched to match
with the legs of the header channel. If installed in an
opening with a sloped sill, the bottoms of the side
channels should be trimmed accordingly.
The opening left after old aluminum fin-mounted
windows are removed can be similarly covered 
with F-Channels, effecting a better sealed finished
installation, and eliminating the need for applied
pieces to act as a blindstop.
Window Fitters Guide to Window Installation 
89                ©2022 AWDI, LLC Do not reproduce without permission
Finished Installation using F-Channel.
Old Steel
Window
in Brick
Opening
New Vinyl
Window
Installed
with
F-Channel
Remove
Old
Window
Shear off
Blindstop
Install
F-Channel
on Sides
and Header.
Cap 
Opening
NOTCH FOR
BEST FIT
AFTER
SAMPLE MANUAL

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