Every homeowner struggles to decide when it’s really time to make a large repair or replace something expensive, like an appliance or old flooring. Windows are one such major expense that can be hard to judge when an upgrade is truly needed—or when a pushy salesperson has simply convinced you an upgrade is needed. Here’s how to tell if you really do need to replace those windows.

Leaks and drafts

The most obvious sign that you actually need to replace your windows is leaking—if water is getting into your home every time it rains, your current windows have stopped performing one of their most basic tasks. Water intrusion can be subtle—if you notice the window frames get damp when it rains, or discover mysterious puddles on the sill or floor near your window, something’s not right. It’s possible that it’s just old, failing caulk, so you can try to re-caulk your windows. But if that fails, it’s time to replace them.

Another sign it’s time to replace your windows is drafts. If you can feel the wind blow through your windows—especially if you’ve re-caulked recently—the time has come to do something about it. There are cheaper options to consider, like window inserts, but these can have downsides (like not being able to open your windows), so opening your wallet and bringing in some contractors might be a better option.

Indoor air quality

Related to leaky windows is one of the most subtle signs you need to replace them: The quality of your home’s interior air. If you suddenly notice you’re having allergy attacks even when you’re indoors, or you notice you can smell the lighter fluid every time your neighbor fires up their grill, your windows may be the culprit. You can test your home for drafts to confirm that it’s your elderly windows, starting with a visual inspection and then using incense or a lit candle to observe air currents. If your windows are letting in the outside air, you can try to re-caulk or eliminate the problem as noted, but chances are good you’ll just need to replace them.

High utility bills

There could be several reasons why it’s suddenly costing you a lot more to heat or cool your home, but if your windows are older than 10 years (the length of most standard warranties), they should be on your list of suspects (especially if you can feel a draft). Older windows just aren’t going to offer the same insulation and weather-sealing properties as newer windows, so they can be responsible for a higher utility bill. If you’ve investigated other possible causes for that huge bill and come up empty, it’s time to consider new windows.

Cloudy glass

If the glass in your window has become hazy, almost like it has a film, it usually means the seal around the frame has failed. That allows the inert, insulating gas between the panes to escape, and allows moisture to enter, which then evaporates, leaving behind deposits that form a hazy coating. It’s possible to repair foggy glass, but it’s not easy, and the fix may not last very long if the rest of the window is in poor shape.

One caveat before you opt to replace a fogged-up window: Check your warranty, if you have one. Different replacement window manufacturers have different warranty policies, which also vary depending on the product installed. Some companies may replace glass that’s become fogged up or otherwise damaged for a surprisingly long time (you’ll still have to pay labor costs, usually), so it’s worth checking into.

Stuck windows

Whatever type of windows you have, if they’re meant to open, and if you can’t open them easily, it’s possible that they need to be replaced. You can investigate to see if there’s another explanation—years of sloppy paint jobs can seal a window pretty firmly, for example—but if you come up empty, you might have swollen, rotten frames or rusted mechanisms from moisture intrusion, which means it’s time to remove those old windows and start fresh.

Keep in mind that the above indicators are more important in determining whether to replace your windows than just their age. Not all windows are created equal, and how well they’ve been maintained over their lifespan can make a difference, too.