What actually fails on a door in this climate?
The hardware and the weatherstrip, not the slab. Cheap latches stiffen and lose alignment through repeated freeze cycles, and compressed weatherstrip stops sealing long before the door itself looks worn.
Fibreglass or steel?
Fibreglass for an exposed front entry — it will not warp, dent or rust and it insulates better. Steel is a sound, lower-cost choice for a sheltered or secondary door.
Can you replace just the door and keep my frame?
Sometimes, if the frame is square, sound and dry. More often the frame is the reason the old door stopped sealing, and reusing it means paying twice. We measure and tell you which case you are in.
Do patio doors lose more heat than windows?
A patio door is mostly glass, so a poorly specified one does. Triple-glazed with a warm-edge spacer, a modern patio door performs close to a window of the same area — which is why we recommend triple on patio doors even where double is fine elsewhere.