Replacing windows cuts the average energy bill by up to 13 percent, per ENERGY STAR, not the 30 or 50 percent some ads imply, plus less outside noise and a bump in resale value. The changes you’ll notice first are comfort and noise, not the bill: fewer cold spots near the glass, and windows that open and lock the way they should.
The Energy Number, From the Actual Source
ENERGY STAR says it plainly on its own site. Replace old single-pane windows with ENERGY STAR windows, and your energy bill drops by up to 13 percent on average. That’s a nationwide average, not a number for your specific house. The real figure moves with how many windows you replace. It also depends on what heats and cools your home now, and how leaky the rest of your house is.
Two parts drive most of that number: the glass and the frame seal. A modern replacement window uses two or three panes of glass. It also has a low-E coating and argon gas between the panes, which slows heat moving through it. A tight frame seal and new weatherstripping stop air leaking around the sash. On an older window, that leak is often the bigger loss, not the glass.
St. Louis puts both parts of a window to work harder than a mild climate does. Summers run hot and humid, winters swing well below freezing, and the freeze-thaw cycle in between is what actually stresses a frame seal. An old seal that survived ten mild winters somewhere else can fail faster here.
What You’ll Notice Before You See a Lower Bill
The energy savings build up slowly, over a full season. These other changes show up in the first week, side by side with what an old window was actually doing.
| What you notice | Old window | New window |
|---|---|---|
| Outside noise | A single pane blocks very little sound from a busy street or a train | Two panes with more space between them block a lot more |
| Near the glass | A broken seal lets air leak right where you sit | A new seal closes the gap, so it feels the same as the rest of the room |
| Condensation | Fogs or drips in winter because the glass itself is too cold | A low-E, insulated pane stays closer to room temperature |
| Opening and locking | Frame has swelled or shifted out of square, lock won’t catch | Built to the right size, opens and locks the way it should |
The last row matters for more than convenience. If a bedroom window is also your exit in a fire, a lock that won’t catch or a sash that won’t budge is the whole problem.
One Window or the Whole House?
Two things decide that: how old your windows are, and how many problems you already have with them. It’s rarely all or nothing. If you’re not sure your windows have reached that point yet, our guide on how to know when to replace windows covers the warning signs. This section assumes you’re past that and deciding how much to do.
Replace just one window when only one is failing, like a broken seal or a lock that won’t catch. If the rest of your windows are fine, there’s no reason to touch them yet.
Replace the whole house when several windows show the same problems at once: more than one draft, more than one broken lock. Doing them all together means one crew and one trip, instead of several separate jobs spread out over time.
Think about timing if you plan to move soon. The comfort and quiet start the day the windows go in. The energy savings take longer, often a full season. Sell soon after, and you won’t see much of that part yourself.
Trying to pick the right glass or frame? Our guide to choosing energy-efficient windows covers that part of the decision.
This guide is for replacing a window that’s already there. A brand-new opening in a wall with no window yet, or a full teardown, is construction work, not a window swap, and it needs a different kind of estimate.
What a Warranty Should Actually Cover
Ask about two different warranties before you sign anything. They cover two different problems, and a great window can still leak if it’s installed wrong.
| Warranty | What it covers |
|---|---|
| Manufacturer’s product warranty | The window itself: the glass seal, the frame, the hardware. Terms change by brand and by product line, so ask for the exact years on your specific window. |
| Installer’s workmanship warranty | The install: was it set square, sealed and flashed the right way. STL Windows and Doors has installed replacement windows across the St. Louis area since 2014, and backs every install with a 10-year workmanship warranty. |
The window’s own warranty won’t fix a bad install, and the install warranty won’t fix a failed seal. Ask any installer you’re comparing what their workmanship warranty actually covers, and get it in writing.
Frequently Asked Questions
Need Help Deciding?
Not sure if you need one window fixed, or a full house replacement? A free on-site estimate, no obligation, is the fastest way to find out. We’ll look at what’s actually happening with your windows, then give you a straight answer, not a push toward the most expensive option. See finished jobs in our photo gallery, or call (314) 277-5952.
