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4. When To Replace Your Windows: Signs, Timing, And How To Decide (2026)

Updated for 2026 • Based on industry data, manufacturer specifications, and St. Louis dealer experience

You’ve probably wondered whether your windows have reached the point where replacement makes sense. Maybe you’ve noticed drafts. Maybe your energy bills have crept up. Maybe a contractor mentioned during a different project that your windows look tired. This is the decision-stage question most homeowners face several years before they actually do anything about it — and it’s a question worth answering carefully because window replacement is a significant investment.

This guide gives you the decision tools: the specific signs your windows are failing, how to tell repair from full replacement, when in the year to do the project, when in your homeownership timeline it makes sense, and what to do once you’ve decided. We’re an exclusive Marvin dealer in St. Louis, but the framework here is brand-neutral and applies to any window replacement decision.

The short answerReplace your windows when you’re seeing multiple signs of failure (drafts, fogging between panes, difficulty operating, rising energy bills, visible damage) rather than one isolated symptom. If your windows are 20+ years old and showing any of those signs, replacement is usually the right call. If they’re newer than 15 years and only one window has a single problem, repair often makes more sense than full-house replacement. The best time of year to schedule the project in St. Louis is generally spring through early fall — manageable weather for installation, but factor in 6–12 week lead times from order to install. If you’re staying in your home 5+ years, the energy savings and comfort improvements typically justify the investment. If you’re selling within 2–3 years, expect roughly 67–72% ROI at resale per the 2025 Cost vs. Value Report.

Not sure if you’re ready to replace?Forshaw offers free in-home assessments where we evaluate your existing windows and tell you directly whether replacement is the right call. No pressure, no obligation — just a clear assessment.Call (314) 993-5570

10 signs your windows are reaching end of life

The single best diagnostic is multiple signs across multiple windows. A single symptom on a single window is usually a repair candidate. Multiple symptoms across multiple windows usually means the whole system is reaching end of life.

1. Drafts you can feel near the window

Stand next to the window on a cold day. If you can feel cold air infiltrating around the frame or sash — even with the window closed and locked — the weather seal is failing. Drafts indicate either weatherstripping degradation (often repairable), frame warping or settling (sometimes repairable, often not), or a fundamental seal failure between the sash and frame (usually means replacement).

2. Fogging or condensation between glass panes

This is the most definitive end-of-life sign. If you see fog, moisture, or visible condensation between the two panes of a double-pane window, the insulating glass unit (IGU) seal has failed. The desiccant inside the spacer is saturated, the inert gas fill (argon or krypton) has escaped, and the window has lost most of its insulating value. Standard IGU warranties are 20 years; failure within that window means warranty replacement, failure beyond means full replacement decision.

3. Difficulty opening, closing, or locking

Windows should operate smoothly. If you’re fighting the sash to open it, if the lock no longer engages properly, or if the window doesn’t seal flush when closed, the underlying issue is usually one of: frame settling out of square (structural, often means replacement), hardware wear (often repairable for 10–15 years before replacement), or sash balance failure (often repairable). For a window 20+ years old with operating issues, replacement is typically the answer.

4. Visible rot, warping, or damage on the frame

On wood frames: soft spots when you press on the sill or jamb, visible water staining, fungal growth, or actual rot. On vinyl: warping (particularly on south- and west-facing exposures), cracking, or color failure. On aluminum: corrosion at joints. Frame damage usually progresses faster than it appears; once visible damage is present, the underlying issue has typically been developing for years.

5. Rising energy bills with no other explanation

If your heating and cooling costs have been climbing year over year and your HVAC system is in good shape, window performance degradation may be the cause. Per Heins Contracting’s 2025 analysis, vinyl windows typically lose 10–15% of their original insulating value after 15 years. The degradation is gradual — you don’t notice it from one year to the next — but it shows up in the utility bills.

6. Water staining or damage around the frame

Water stains on the interior wall around a window, peeling paint, drywall damage, or visible moisture intrusion all indicate the weather seal is failing and water is finding its way into the wall cavity. This is more urgent than other signs because water infiltration causes structural damage that compounds over time — rot, mold, and framing deterioration that costs more to fix the longer you wait.

7. Excessive exterior noise

Quality replacement windows substantially reduce sound transmission compared to single-pane or failing double-pane windows. If outside noise (traffic, lawn equipment, neighbors) is increasingly noticeable through closed windows, the seal is degrading. Sound transmission gets worse as the IGU seal weakens and as weatherstripping fails.

8. Visible damage from impact or storm

Cracked glass, broken hardware, or frame damage from severe weather (St. Louis sees real storms regularly) may be repairable for individual windows but should also prompt evaluation of the rest of the system. If one window has impact damage and several others are 20+ years old, replacing all of them at once usually makes more economic sense than repairing one and replacing the others two years later.

9. You can’t comfortably use the room near the window

A practical sign that often gets ignored: if there’s a room you avoid in winter because it’s too cold near the windows, or rooms where furniture has been rearranged to stay away from drafts, your windows are affecting your quality of life. This is a less technical sign than fogging or visible damage but a more concrete one for many homeowners.

10. Your windows are 20+ years old and you’re seeing any of the above

Age alone isn’t a replacement trigger — well-maintained windows can last 30–50+ years. But combined with any of the above signs, 20+ year age substantially shortens the cost-benefit window for repair. At that age, money spent on repair is rarely recovered if you have to replace within a few years anyway.

Repair vs. replace: the decision tree

Not every window problem requires replacement. The decision tree below covers the most common scenarios:

Repair makes sense if…

• Only one or two windows have problems and the rest of the system is performing well
• The window is less than 15 years old and the underlying frame is in good condition
• The problem is isolated to hardware (locks, hinges, balance systems, operators) — these are typically 10-15 year wear items and often replaceable individually
• The problem is glass-only (IGU seal failure on an otherwise sound frame) — the glass unit can usually be replaced while keeping the existing frame
• The problem is weatherstripping — weatherstripping is a routine wear item that should be replaced periodically regardless
• The frame structure is sound and you’re mainly addressing a cosmetic or performance issue

Full replacement makes sense if…

• Multiple windows are showing failure signs across the home
• The windows are 20+ years old and showing any meaningful problems
• The frame structure is compromised (rot, warping, settling, prior unsuccessful repairs)
• Energy efficiency is materially below current standards and your utility costs reflect it
• You’re planning to stay in the home 5+ years and the cumulative energy savings + comfort benefits justify the investment
• Multiple windows would need expensive repairs that approach the cost of replacement
• Your design priorities have changed and the existing windows don’t fit your current aesthetic

The repair-cost threshold

A practical rule: if repair costs exceed roughly 50% of replacement cost on a given window, replacement is usually the better economic choice — because you get a new warranty, new energy performance, and another 20–40+ years of service instead of extending a window that’s already aged. For example: if a 25-year-old window needs $800 in hardware and IGU replacement and a new comparable replacement would cost $1,400 installed, replacement is the better economic decision even though repair is cheaper upfront.

When in the year is the best time to replace windows?

The straight answer: any time of year is workable in St. Louis, but each season has trade-offs.

Season	Pros	Cons	Best for
Spring (Mar–May)	Mild weather, ideal install conditions, fresh-start timing	Peak demand; longer lead times; less negotiating leverage	Homeowners with flexible timing who want optimal conditions
Summer (Jun–Aug)	Long daylight, dry conditions, school-out flexibility	Hot install conditions; AC loss during install; peak demand	Whole-home projects requiring multiple days
Fall (Sep–Nov)	Optimal install weather, energy savings start immediately	Lead times can push installation into winter; weather risk late season	Homeowners wanting energy savings before winter heating bills
Winter (Dec–Feb)	Off-season pricing, shorter lead times, faster scheduling	Heat loss during install; weather can delay; less comfortable working conditions	Cost-conscious projects; small-scope replacements

The lead-time reality

Custom-manufactured windows from premium brands (Marvin, Pella Reserve, Andersen A-Series) typically have 6–12 week lead times from order to delivery in 2026. Vinyl windows from stock-size programs can be faster (2–6 weeks). What this means practically: if you want spring installation, you’re placing your order in winter. If you want energy savings starting in fall, you’re consulting in summer.

The mismatch between when shoppers think about windows (fall, when bills spike) and when they need to start the process (months earlier) is one reason this decision often gets delayed an entire year. Starting the consultation process well before your target install date is the most practical timing advice we can offer.

When NOT to install

Two periods genuinely worth avoiding in St. Louis:

• Sustained extreme cold (below 20°F): Sealant and caulk performance degrades; condensation forms during install; HVAC loads spike with windows open. Most quality installers will reschedule rather than push through these conditions.
• Storm season high-risk periods: April-May severe weather windows in particular. Windows being installed are vulnerable to wind and rain damage. Most installers schedule around forecasts.

When in your homeownership timeline is the right time?

If you’re staying long-term (5+ years)

The economics favor doing it sooner. Per ENERGY STAR data, replacement windows save approximately 12% annually on heating and cooling costs (the This Old House 2024 customer survey put the average at $510 per year). Over 10 years, that’s $3,000–$6,000 in cumulative energy savings depending on your home and current windows. Add the comfort improvements and reduced maintenance, and the longer you wait, the more value you forfeit. If your windows are clearly failing, delaying replacement two years to “think about it” often costs more than just doing the project.

If you’re selling within 1–2 years

Per the 2025 Cost vs. Value Report, vinyl window replacement recoups 67–72% of project cost at resale. You won’t recover the full investment. But: failing windows are a meaningful negative factor in home inspections and buyer perception. If your windows are visibly aged or showing problems, replacement before listing typically pays for itself in faster sale and reduced buyer price negotiations — even if not in pure ROI. Consult with your realtor about whether prospective buyers in your neighborhood factor windows heavily in their decisions.

If you’re selling within 3–5 years

The middle ground. The economics are tighter. The factors that matter: how clearly failing are the current windows (the worse they are, the better the ROI of replacement), whether your local market rewards visible upgrades, and whether you’d enjoy the windows yourself during the remaining ownership period. Often the right call is to replace if windows are visibly aged but defer if they’re still performing adequately.

If you just bought the home

New homeowners often replace windows in year 1–2 if the inspection flagged issues. This is usually fine economically because you’re likely planning long-term ownership and the upfront investment amortizes well. Caveat: if you’re still settling into the home, give yourself time to understand the existing windows before committing. We see new owners replace windows that, in hindsight, were performing acceptably — the perception of “old windows” can outpace the reality.

Should you replace all windows at once or in phases?

A legitimate decision shoppers face when the project total feels overwhelming. Both approaches have valid uses.

All at once: when it makes sense

• Quantity discounts apply. Most quality dealers (including Forshaw) offer better per-window pricing on whole-home projects of 10+ windows. The savings can be 5–15%.
• Single installation event. One crew, one debris removal, one disruption period. Less aggregate disruption than two or three separate projects.
• Consistent aesthetic. All windows match exactly — same brand, line, color, finish, hardware. Different installation years can produce subtle differences in color or finish that show over time.
• Energy efficiency benefits compound. Mixed-age window systems perform at the level of the weakest windows. Replacing some while keeping others delays the full energy savings.
• Single warranty cycle. All windows start their warranty period together — simpler to track and easier to coordinate any future service.

Phased: when it makes sense

• Budget constraints make the full project infeasible. Doing half the windows now and half in 12–18 months is far better than not starting at all.
• Some windows are clearly failing while others are sound. If 8 of 16 windows are 30+ years old and 8 are 10 years old, replacing the 8 older ones first is reasonable.
• You’re testing a brand or product line. Doing 3-5 windows first lets you experience the brand, installation quality, and finished aesthetic before committing to the full home.
• Phased construction work. If you’re renovating room by room, replacing windows during each room’s renovation makes sense.

Phasing strategy: which windows first?

If you go phased, the typical priority order:

• First: Windows showing the worst failure signs (visible damage, IGU fog, operation problems) — these are losing the most energy and creating the most comfort issues
• Second: South- and west-facing windows — highest UV and thermal exposure, fastest deterioration
• Third: Rooms you use most (living, master bedroom, kitchen) — maximum comfort impact for your daily use
• Fourth: Remaining windows — typically the lowest-priority bedrooms, basement, and seasonal-use rooms

How long does the replacement project actually take?

Setting realistic expectations on timeline:

• Consultation to written quote: 1-2 weeks typically. Most quality dealers provide free in-home or showroom consultations. Quote generation takes a few days after measurement and product selection.
• Quote to signed contract: Your timeline. We don’t pressure same-day decisions; many homeowners take 2-4 weeks to compare quotes and decide.
• Contract to manufacturing: 1-2 weeks. Order placement, final measurements verified, manufacturing slot scheduled.
• Manufacturing lead time: 6-12 weeks for premium custom-manufactured windows (Marvin, Pella Reserve, Andersen A-Series). 2-6 weeks for stock-size vinyl programs.
• Installation: 1-3 days per crew for typical residential projects. Most St. Louis homes (10-15 windows) install in 2-3 days; larger projects (20+ windows) take 3-5 days.
• Permit and inspection: If required by your municipality, typically completed during or just after installation. Doesn’t usually extend the homeowner-experienced timeline.

Total project timeline: typically 2-4 months from consultation to completed installation. Plan accordingly.

St. Louis-specific considerations

Climate stress accelerates the timeline

St. Louis sees real temperature stress on windows: sub-20°F winter mornings, 95°F+ summer afternoons, severe storms periodically. Budget vinyl windows that might last 25 years in mild climates often need replacement in 15-20 years here. If you bought your home with builder-grade windows installed in the late 1990s or early 2000s, you’re in the prime replacement window now — those windows are reaching end of life.

Older housing stock

Many St. Louis neighborhoods have homes built before 1970, where wood frames may have settled, suffered water damage, or been altered by previous (sometimes poorly executed) replacements. If your home is in Soulard, Lafayette Square, Compton Heights, parts of Kirkwood, Webster Groves, Clayton, University City, or similar pre-war neighborhoods, full-frame replacement (rather than insert) is more often the right approach because of frame condition. Our consultation includes evaluation of the existing frame to determine which installation method fits your project.

Historic district requirements

If your home is in a historic district (the list above includes several), local architectural review may require specific products, divided-light configurations, or matching to original profiles. This affects which brands and product lines are eligible and may extend the timeline by adding review board approval. Marvin Ultimate is widely approved in St. Louis historic districts; many vinyl and mid-tier products are not.

Permit requirements

Most St. Louis municipalities require permits for full-frame replacement; some require permits for any window work. Permit cost is typically passed through at the actual municipal cost. Quality dealers handle permit pulling as part of the installation service — ask whether permits are included or pass-through in your quote.

What to do once you’ve decided to replace

Practical sequence:

• 1. Get 2–3 written quotes from established dealers. Specify the same product line and installation type to each dealer for apples-to-apples comparison. Avoid in-home sales models that pressure same-day decisions.
• 2. Verify the quote includes everything. Product line, glass package, installation type (insert vs full-frame), trim and finishing, permits, warranty terms, payment schedule, expected timeline. Lump-sum quotes without itemization are sales tactics, not real quotes.
• 3. Visit a showroom if possible. See operable windows before deciding. Compare wood species, finishes, hardware operation, and color samples in person. Photos and videos don’t convey what you’ll actually live with for 30+ years.
• 4. Check warranty details specifically. Length of coverage on glass, finish, frame, hardware. Whether transferable to subsequent owners. Whether labor is covered by manufacturer or dealer.
• 5. Confirm the installation team. Ask whether installation is by the dealer’s trained team or subcontracted. Ask about installation accountability if issues arise. Ask for installer references on similar projects.
• 6. Decide on your timeline, not the dealer’s. Take the quote home. Compare to others. Sleep on it. Quality dealers don’t pressure same-day decisions.
• 7. Sign and schedule. Once you’ve decided, the dealer handles manufacturing order, scheduling, permits, and installation logistics.

Why Forshaw for window replacement evaluation in St. Louis

Forshaw has been a family-owned St. Louis business since 1871. We’re an exclusive Marvin dealer for our window and door division.

• Direct assessment, no pressure. Our consultation includes a frank evaluation of your existing windows. If your windows aren’t actually ready for replacement, we’ll tell you. If they are, we’ll explain why and what your options look like.
• Insert and full-frame, both done well. We sell roughly even numbers of insert and full-frame replacements. The right approach depends on your existing frame condition, not on a default preference. Our evaluation tells you which fits your specific project.
• Transparent, itemized quotes. Line-by-line pricing showing product, glass package, installation type, permits, warranty, and timeline. Take the quote home. Compare it to others. Decide on your timeline.
• Showroom evaluation. See operable Marvin windows side by side. Compare wood species, finishes, hardware, and operating mechanisms before committing.
• Local installation accountability. Our trained installation team handles your project from consultation through completion. Marvin’s manufacturer warranty covers parts; our workmanship warranty covers labor.
• Historic district experience. We work regularly in Clayton, Ladue, Kirkwood, Webster Groves, University City, Lafayette Square, Soulard, and similar preservation neighborhoods.

Get a direct assessment from ForshawWe’ll evaluate your existing windows, tell you whether replacement is actually the right call, and — if it is — walk you through the options. Free in-home consultations, no obligation, no pressure to decide on the spot.Call (314) 993-5570or schedule a free consultation online

Frequently asked questions

How do I know when it’s time to replace my windows?Look for multiple signs across multiple windows rather than a single problem on a single window. Definitive end-of-life signs: fog or moisture between glass panes (failed IGU seal), drafts you can feel with windows closed, visible rot or warping on the frame, difficulty operating, water staining around the frame. A single sign on one window is usually a repair candidate. Multiple signs across multiple windows usually means the whole system is reaching end of life.

What’s the best time of year to replace windows?Spring through early fall offers optimal install conditions in St. Louis. Spring and summer are peak demand periods with longer lead times. Fall combines good install conditions with energy savings that start before winter heating bills. Winter offers off-season pricing and shorter lead times but has weather-related install challenges. The single most practical timing advice: start the consultation process 3-6 months before your target install date to account for 6-12 week manufacturing lead times on premium custom windows.

Should I replace all my windows at once or in phases?Both approaches are legitimate. All-at-once typically delivers 5-15% per-window cost savings through volume pricing, consistent aesthetics, and a single installation disruption. Phased replacement makes sense when budget constraints prevent doing all at once, when some windows are clearly failing while others are sound, or when you’re testing a brand before committing. If you go phased, replace the worst-performing windows and south/west-facing exposures first — those have the highest energy and comfort impact.

Is it worth replacing 20-year-old windows?Usually yes, especially if you’re seeing any performance issues. 20-year-old windows are typically at the end of their useful service life for vinyl and aluminum products and reaching the point where repair costs no longer make economic sense. The exceptions: premium fiberglass (30-50+ year typical lifespan) and well-maintained wood-clad (25-40+ year typical lifespan) may still have meaningful service life remaining at 20 years if they’re showing no failure signs.

How long does window replacement take?Total timeline from initial consultation to completed installation is typically 2-4 months. Breakdown: consultation to quote (1-2 weeks), quote to signed contract (your timeline), contract to manufacturing (1-2 weeks), manufacturing lead time (6-12 weeks for premium custom; 2-6 weeks for stock vinyl), installation (1-3 days for typical St. Louis homes). The manufacturing lead time is the longest and least flexible part — plan accordingly.

Should I repair or replace my windows?Repair if: only one or two windows have problems, the windows are less than 15 years old, the issue is isolated to hardware or glass (not the frame structure), or the frame is sound. Replace if: multiple windows show failure signs, the windows are 20+ years old, the frame structure is compromised, energy efficiency is materially below current standards, or repair costs would exceed roughly 50% of replacement cost. A free assessment from a quality dealer can tell you which applies to your specific project.

How much do replacement windows cost in St. Louis?Industry-published 2026 ranges: $750-$1,600 per window installed for mid-tier and premium products. The national average per Modernize’s 2026 survey of 1M+ projects is $1,047 per window. For a typical St. Louis home of 10-15 windows, full replacement typically falls between $7,000 and $20,000 depending on materials, brand, and installation type. See our detailed replacement window cost guide for breakdowns by project size and material category.

Will replacement windows pay for themselves?Not in pure energy savings on a typical St. Louis home, no — the math rarely works out for that alone. ENERGY STAR data shows ~12% annual savings on heating and cooling, averaging $510/year per This Old House’s 2024 survey. But there are other returns: home resale value (the 2025 Cost vs. Value Report shows 67-72% ROI at resale for vinyl), comfort improvements (drafty windows make rooms unusable in winter), reduced maintenance, and improved curb appeal. Most homeowners replace windows because the existing ones have problems, not because they’re seeking ROI.

Do I need permits to replace my windows in St. Louis?Most St. Louis municipalities require permits for full-frame window replacement. Some require permits for any window work. Insert replacements (where the existing frame stays in place) sometimes require permits and sometimes don’t depending on the municipality. Permit costs are typically passed through at the actual municipal cost. Quality dealers handle permit pulling as part of the installation service — verify whether permits are included or pass-through in your quote.

What happens during a window consultation?A typical Forshaw consultation includes: (1) evaluation of your existing windows with notes on condition, age, and performance issues; (2) measurement of each opening; (3) walk-through of Marvin product line options that fit your project; (4) discussion of installation approach (insert vs full-frame) based on what we found; (5) written itemized quote with specific products, glass package, installation type, permits, warranty, and timeline. We don’t pressure same-day decisions. You take the quote home, compare to others, and decide on your timeline.

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