How do I know if my windows need to be replaced?
Replace a window when the frame or sill is rotted, fog or moisture sits between the panes because the seal has failed, it is single-pane and drafty, or it will not open, close or stay open. A broken balancer, lock, crank, worn weatherstripping or a cracked pane can often be repaired instead, and condensation on the inside glass usually means high indoor humidity.
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By Kasra Taheri, Founder, LoclisPublished
Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.
Step by step
Read when to stop and call a pro, further down this page, before you start.
Step 1: Look between the panes
Check double-pane glass for fog, droplets or a cloudy film between the panes, which points to a failed seal.[3]
Step 2: Note where condensation forms
On a cold morning, see whether moisture is outside, inside or between the panes, since only between the panes is a window failure.[2]
Step 3: Check indoor humidity
If the inside glass fogs in winter, check indoor humidity with a hygrometer, aiming for 30 to 35 percent.[3]
Step 4: Open and close each window
Make sure each sash opens, closes, locks and stays open on its own, and note any that slam or stick.[2]
Step 5: Feel for drafts
On a cold, windy day, hold the back of your hand near the sash edges, lock rail and frame and note where you feel air.
Step 6: Press on the wood
Press your thumb firmly on the sill and the bottom corners of wood sashes and frames; wood that feels soft or spongy points to rot. Do not scrape or sand painted wood.
Step 7: Check glass and putty
From outside, look for cracked or broken glass and for cracked or missing glazing putty on older wood sashes.[5]
Step 8: Look for gaps at the frame
Look for visible gaps between the window frame and the wall, inside and out, and for water stains below the window.[5]
Step 9: Check for single-pane glass
Look at the edge of the glass, or for a label on the frame, to see whether each window has one pane or two.
Step 10: Write down what you find
List each window with its problems so you can tell a repair from a replacement and get like-for-like quotes.
Your windows probably need replacing if the frame or sill is rotted, there is fog or moisture trapped between the panes, they are single-pane and drafty, or they will not open, close or stay open properly. Many other problems, such as a window that slams shut, a broken lock or worn weatherstripping, can be repaired for much less. And condensation on the inside glass is usually a humidity problem, not a window problem.
ENERGY STAR names three major reasons to replace: single-pane windows, windows with air leaks and degraded sills and sashes, and windows that do not open or are painted shut.[1] Here is how to check for each, and how to tell a repair from a replacement.
Signs a window needs replacing
Fog or moisture between the panes. When you see condensation between the two panes of a double-pane window, the seal has failed.[3][4] Andersen notes that you cannot stop it from forming once the seal breaks,[3] and the condensation means the window is no longer performing well.[3] This is the clearest single sign, but check the warranty before you buy a whole new window.
Rot in the sill, sash or frame. Soft, dark or crumbling wood, peeling paint that keeps coming back, or water stains on the wall under the window all point to water getting in. ENERGY STAR warns: "Degraded windows can also leak water into your walls causing more problems and allow insects and other pests to enter your home."[1] Look at what is above the window too. Andersen's installer guidance says: "If you notice a roof is directing water at a window, that might be a clue there could be rot."[6] Rot that has reached the frame usually means a full replacement, not a repair.
Windows that will not open, close or stay open. Andersen points out that a window that is hard to open or will not stay open may have something warped or broken inside, and that it can be a safety concern in a fire.[2] Windows painted shut fall into the same group.
Single-pane glass. ENERGY STAR is blunt: "Single-pane windows are big energy wasters."[1] They are cold to sit near in winter and let in more summer heat.
A frame out of square. If sashes bind, gaps are uneven, or the header above the window dips, the opening may have moved. Andersen lists sagging headers and windows clearly out of square as details an installer looks for.[6] That is a job for a contractor to assess, because it can mean more than a window swap.
Condensation: where it forms matters
Condensation confuses a lot of homeowners, so check where it is:
- Outside the glass. Condensation on the outside of the glass is dew, most common on spring and fall mornings, and Andersen says it is a sign the window is insulating well.[3] Nothing to fix.
- Inside the glass. Condensation on the inside glass in winter means indoor humidity is too high, not that the window is broken.[3][2] In winter, Andersen suggests aiming for 30 to 35 percent indoor humidity.[3] The Virginia Energy Savers Handbook adds that condensation in cold weather may simply be caused by excessive indoor humidity, but might also be caused by cold air leakage around the glass,[5] so check those windows for drafts too. Do not ignore it: Too much condensation can cause the paint to peel on your window's sash and damage the window frame.[3]
- Between the panes. A failed seal, as above.
Problems that can usually be repaired
Not every faulty window needs replacing. Andersen says a broken balancer, lock or casement crank can often be replaced, and a broken sash can sometimes be replaced on its own if the rest of the window is in good condition, meaning the frame is square and there is no rot.[2] A broken balancer usually shows itself when the window slams shut or is very hard to open.[2] Single issues such as a missing screen, damaged weatherstripping or broken grilles are usually worth repairing.[2]
Drafts and rattles often have simple causes. The Virginia Energy Savers Handbook notes that loose windows not only lose heat through air leakage but also cause uncomfortable drafts in winter.[5] Its advice is to check that the lock works and that there is weatherstripping in the side channels.[5] It also says: "There should be no visible gap between the window frame and wall surface."[5] Gaps there are usually a caulking job; see how often to check weatherstripping and caulk.
Older wood windows can often be restored. The handbook explains that small cracks in glazing putty may only need a good coat of paint, larger cracks or missing putty mean the sash needs reglazing, and a window in particularly bad shape may make more sense to replace than repair.[5] Broken or cracked glass should be fixed promptly, since even cracked panes of glass allow a significant loss.[5]
If the windows are sound but single-pane, storm windows are a cheaper middle path. ENERGY STAR says certified storm windows cost one-half to one-quarter as much as common replacement windows and can be installed inside or outside the existing window.[1]
Do not replace for energy savings alone
Lower bills are real, but modest. ENERGY STAR says new windows may not pay for themselves in energy savings alone.[1] Replace for rot, failed seals, broken operation, safety or comfort, and count the savings as a bonus. What window replacement costs in Virginia covers the price side.
Stop and call a pro if
- The sill, frame or wall below the window is soft or stained, which can mean water damage inside the wall.
- The header above the window sags or several windows bind at once.
- The window is above the first floor and checking it would mean a ladder.
- The house was built before 1978 and the problem involves scraping, sanding or removing painted parts. If your home was built before 1978, it may have lead-based paint,[7] and the EPA recommends hiring a certified lead inspector or risk assessor to test the surfaces you plan to renovate.[7]
- A bedroom window will not open at all, since it may be the room's way out in a fire.
Getting it looked at
Get more than one opinion, especially when a seller recommends replacing every window. Virginia's Board for Contractors advises homeowners to solicit at least three bids, make sure all of them are based on the same specifications, and not automatically accept the lowest.[8] Read how to measure for replacement windows before quotes, browse window replacement businesses or window repair, find exterior businesses around Blacksburg, or see all exterior answers.
To get it looked at, describe the window problem once and local businesses will reply.
Common questions
- Does fog between the panes mean I need a new window?
- It means the seal on that glass unit has failed, and you cannot stop the fogging once it starts. Check the warranty first: Paradigm, for example, asks owners to file a claim to see whether a seal failure is covered under its 20-year or lifetime warranty. Some windows can take a new sash or glass unit without replacing the whole window.
- Is condensation on the inside of my windows a sign they are failing?
- Usually not. Andersen says interior condensation means indoor humidity is too high, not that the window is broken, and suggests 30 to 35 percent humidity in winter. The Virginia Energy Savers Handbook adds that cold air leaking around the glass can also cause it, so check for drafts too.
- My window slams shut or will not stay up. Do I need a new one?
- Not necessarily. Andersen says a broken balancer shows itself when the window slams shut or is very hard to open, and it is often a fixable repair if the frame and sash are otherwise sound.
- Will new windows pay for themselves in energy savings?
- Rarely on their own. ENERGY STAR says new windows may not pay for themselves in energy savings alone. Replace for rot, failed seals, broken operation or comfort, and treat lower bills as a bonus.
- Are storm windows an alternative to replacing old single-pane windows?
- Often, if the windows are otherwise sound. ENERGY STAR says certified storm windows cost one-half to one-quarter as much as common replacement windows and can go on the inside or outside of the existing window.
- Should I replace all my windows at once?
- Not if only some have failed. Andersen notes that some homeowners replace one floor or one room at a time to spread out the cost, while replacing everything at once gives a consistent look and installation.
Sources
- [1] High Performing Windows or Storm Windows, ENERGY STAR (U.S. Environmental Protection Agency). Checked October 27, 2026.
- [2] 6 signs it's time to replace your windows, Andersen Corporation. Checked October 27, 2026.
- [3] Condensation on windows: What causes it and how to manage it, Andersen Corporation. Checked October 27, 2026.
- [4] Frequently Asked Questions, Paradigm Windows. Checked October 27, 2026.
- [5] The Virginia Energy Savers Handbook, Third Edition, Virginia Department of Mines, Minerals and Energy and Virginia Tech. Checked October 27, 2026.
- [6] How to assess windows for replacement, Andersen Corporation. Checked October 27, 2026.
- [7] Lead-Safe Renovations for DIYers, U.S. Environmental Protection Agency. Checked October 27, 2026.
- [8] What You Should Know Before You Hire a Contractor, Virginia Board for Contractors (DPOR). Checked October 27, 2026.
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