Once the heat comes on
Summer hides a bad window. Once the heat is running, the problems surface. There's the draft you can feel from the couch, and the bedroom that never quite agrees with the thermostat. Old single-pane glass gets cold enough to chill the air right next to it, and that chilled air slides down the pane and rolls across the floor, which is the draft people blame on gaps even when the window is shut tight. On cold mornings, single panes also collect condensation on the room side, and over the years that moisture is what rots sills and stains the paint below them.
Every fall when the heat comes on, the window calls we get shift away from broken glass and toward cold rooms, and they usually involve windows that had been on the list for years without ever making the top of it. If what you're seeing is fog trapped between the panes of a double-pane window, that's a failed seal rather than a winter problem, and we wrote up how we diagnose it separately.
What's inside an efficient unit
The parts that do the work
The working part of a modern window is the insulated glass unit: two panes sealed around a spacer, with the gap between them filled with a gas that conducts heat poorly, usually argon. A low-e coating, a metallic layer too thin to see, sits on the glass and reflects room heat back inside while letting daylight through. Warm-edge spacers cut down the cold band around the perimeter of the glass, which is where condensation shows up first.
When you're comparing units, the label does the math for you. Look for the NFRC sticker and the U-factor printed on it, which measures how readily heat escapes through the whole window. Lower is better, and it's the number worth comparing across quotes.
The difference you notice at home
The glass surface stays close to room temperature, so the cold-air slide off the pane settles down and the seat by the window comes back into use in January. The furnace cycles run shorter because the house holds what it makes. Street noise drops as well, which surprises people who replaced their windows for the heating bill.
As for that heating bill, how far it comes down depends on how many windows you're replacing and what's in the openings now. Anyone who promises an exact savings figure before standing in your living room is guessing.
You might not need whole new windows
If your frames are sound, an insulated unit can often replace the glass in the frame you already have, which is a smaller job than tearing the window out. Full replacement earns its keep when the frame itself has failed, rot in the sill or a sash that no longer sits square. Our window repair and replacement page walks through how we decide which one a window needs.
Where Energy Trust of Oregon fits in
Energy Trust of Oregon is the nonprofit that runs energy-efficiency incentives for customers of the state's major utilities, and its offers have covered window upgrades among other home improvements. The specifics change from year to year, so before you order glass, check the current offers at energytrust.org and ask whichever contractor you choose what documentation an incentive requires, usually the specs and labels from the new units. A few minutes of paperwork attached to a job you were doing anyway is the easiest kind of help to take.
If this is the year the cold room gets fixed, the first step is small: a free written estimate that tells you whether your openings need new glass or whole new windows, and what the lead times look like. Call and tell us which rooms go cold, and we'll take it from there.
Clear Works Glass, based in SE Portland. Call (503) 887-8329. Monday to Friday 7 to 5, Saturday 8 to 2, emergency line 24/7. Free estimates. Oregon CCB #261682, bonded and insured.