Two identical windows, installed on the same street in the same week, can perform completely differently. The one that leaks air is rarely the cheaper window. It is usually the one where the crew was on the fifth house that day.
Here is what actually happens in the twenty minutes after the old window comes out, and why it matters more than the sticker on the glass.
The gap nobody mentions
A replacement window does not fit its opening exactly. It cannot, because it has to go in, which means it is ordered slightly smaller than the rough opening, leaving a cavity of roughly a quarter to half an inch on all four sides.
That cavity is a direct path from outside your house to inside it. Nothing about the window's own construction closes it. All the numbers on the sticker - the U-factor, the argon fill, the Low-E coating - describe the performance of the unit, and none of them describe the hole around the unit.
Which is why a well-specified window installed carelessly will lose to a modest window installed properly, every time.
The four steps
This is what we do on every full window we install, in this order:
RWD flashing tape
Applied around the opening before the window goes in. Its job is not to make the wall waterproof - it is to give any water that does get behind the trim a path back out, instead of into the framing. The assumption is that water gets in eventually; the tape decides where it goes.
Low-expansion foam in every gap
The cavity gets filled all the way around. Not tacked at the corners, not partly; the full perimeter. This is the step that actually stops the draft, and it is the one most often rushed.
Interior caulk
A clean bead where the frame meets the interior trim. It seals the last of the air path and it is also what makes the finished window look like it belongs there rather than like something dropped into a hole.
Foam around the exterior
The outside gets sealed too, before the trim wrap goes on. Sealing only the inside leaves the cavity open to the weather from the other direction, which is how water gets to sit in it.
None of it is exotic and none of it is expensive in materials. It is time, and time is what gets cut when a crew has five houses booked.
Pricing a full window replacement?
Full window replacement from $834 (tax not included)
Text us a photo of the window and a rough size. We send a written price, usually within the hour during business hours, with all four sealing steps and the trim wrap in it. We come out to measure only after you approve.
Why the foam has to be the right foam
This is the detail that separates the two cans on the shelf, and it has consequences you will live with.
Standard expanding foam keeps growing after it is applied. In a window opening that pressure has nowhere to go except against the frame, and it bows it inward. A bowed frame means sashes that bind or will not lock, a window that gets harder to operate over the first year, and in the worst cases glass carrying stress it was never designed for.
Low-expansion foam fills the cavity and stops. Same tool, same twenty minutes, different can. When someone tells you their new windows are hard to open, this is one of the first things worth suspecting.
How a bad install voids your warranty
This is the part that turns a workmanship question into a money question. ENERGY STAR notes that some manufacturers will void your warranty if their installation instructions are not followed, and Pella's limited warranty is conditioned on the window being installed per Pella's instructions.
So a rushed installation does not only perform worse. It can cost you the manufacturer coverage you paid for, at the exact moment you need to use it. Both layers of protection - the manufacturer's warranty and ours - depend on the same twenty minutes of work.
Our side of that is a lifetime workmanship warranty on the installation, on top of Pella's transferable limited warranty on the window itself. See what each one covers.
How to check your own windows
Four things you can do this week, no tools:
- Feel the perimeter, not the glass. On a cold or windy day, move the back of your hand slowly around the inside edge of the frame. Air at the edges is the gap. Cold glass in the middle is just glass being glass.
- Look for caulk doing a foam job. A heavy bead of interior caulk bridging a visible gap usually means the cavity behind it was never filled.
- Operate every sash. Binding, or a lock that needs a shove to line up, points at a frame that was bowed - often by the wrong foam.
- Check the sill from outside after rain. Water sitting on the exterior sill or a stain running down the trim below the window means water is getting somewhere it should have been steered away from.
If several of those point the same way, the honest news is that it is fixable without replacing the window again. Send us a photo and we will tell you what we think you are looking at.
And if what you see is fog or condensation between the panes rather than a draft at the edges, that is a different problem: the seal of the glass unit itself has failed, and the fix is replacing just the foggy glass, not the window.