The windows in older UK homes are responsible for a surprising proportion of wasted energy every winter. According to the Energy Saving Trust, poorly sealed or single-glazed windows account for up to 25% of a home’s heat loss — meaning that a quarter of the heat your boiler works hard to produce may be quietly escaping through glass, gaps, and frames before it has any chance to warm the room.
The cheapest way to improve old windows' energy efficiency is draught-proofing, which costs as little as £3 to £10 per window as a DIY project and can save a typical UK household £45 to £65 a year on energy bills. Layering secondary glazing film (around £8 to £15 per window) and thermal curtains on top of draught-proofing can cut window-related heat loss by more than half for a whole-home outlay well under £200, without replacing the windows at all. The most important thing to understand is that draught infiltration — cold air entering through gaps in frames and sealant — is often a bigger heat loss culprit than the glass itself, so sealing those gaps first delivers the fastest return. For households in council tax bands A to D with a poor EPC rating, the Great British Insulation Scheme and the Warm Homes Plan may provide additional support toward more substantial window improvements.
- Start with draught-proofing as your first fix — self-adhesive foam or brush strips cost £3 to £10 per window and can save a typical household £45 to £65 a year on energy bills
- Apply secondary glazing film over single-glazed panes for under £15 per window to reduce radiant heat loss and lower the U-value noticeably without replacing the window
- Fit removable acrylic secondary glazing panels for £50 to £150 per window as a step up from film — these outperform film on noise reduction and longevity while still costing a fraction of full replacement
- Hang floor-length thermal curtains with a tight pelmet to trap a layer of still air at the window and cut overnight heat loss by up to 40% compared with unlined curtains
- Re-bed failed or cracked putty around single-glazed panes yourself using linseed oil putty, available for around £8 to £12 a tub, to eliminate a commonly overlooked source of draught infiltration
- Check window frames for gaps between frame and wall and seal them with an appropriate flexible decorator's caulk — a tube costs roughly £4 to £7 and takes under an hour per room to apply
- Stack these measures in combination rather than choosing just one — draught-proofing plus film plus thermal curtains can collectively reduce window-related heat loss by well over half for a whole-home cost well under £200
- Understanding Why Old Windows Lose So Much Heat
- How Much Difference Can Budget Window Improvements Actually Make
- Draught-Proofing Your Windows and Why It Should Come First
- Secondary Glazing Film — A Low-Cost Option Worth Knowing About
- Internal Secondary Glazing Panels — A Step Up in Performance
- Thermal Curtains, Blinds, and Shutters — What the Data Says
- Comparing the Options — Costs, Savings, and Effort at a Glance
- How to Choose the Right Approach for Your Windows — A Step-by-Step Guide
- Are There Any Grants or Funding Available for Window Improvements in 2026
- When Budget Improvements Are Not Enough — Knowing When to Replace
The cheapest way to improve old windows’ energy efficiency is to start with draught-proofing, which costs as little as £3 to £10 per window as a DIY project and can save a typical household £45 to £65 per year on energy bills. Beyond draught-proofing, layering up with secondary glazing film, removable acrylic panels, and thermal curtains can deliver compounding benefits at a total cost well under £200 for most homes — without the need to replace windows entirely.
Understanding Why Old Windows Lose So Much Heat
Old windows waste energy in two distinct ways, and understanding both helps you choose the right fix for your home and your budget.
The first is radiant heat loss, which occurs when warmth radiates directly through the glass from the warmer interior to the cooler exterior. Single-glazed windows — common in homes built before the 1980s — have almost no resistance to this type of heat loss. The key measurement here is the U-value, which describes how quickly a window loses heat. A lower U-value means better insulating performance. A single-glazed window typically has a U-value of around 5.0 W/m²K, compared to around 1.2 to 1.6 W/m²K for a modern double-glazed unit — meaning single glazing loses heat roughly three to four times faster.
The second is convective heat loss through draughts — also written as draught infiltration — which happens when cold outside air enters the home through gaps between the window frame and the wall, around sash runners, through failed sealant, or via deteriorated putty around the glass. This is often the more significant problem in practice, because older windows develop gaps and cracks over decades of seasonal movement, and the cold air they admit chills the room rapidly.
A third, often overlooked issue is thermal bridging, which occurs when the frame material — particularly older metal frames — conducts heat directly from inside to outside, bypassing the glass entirely. Metal frames from the mid-twentieth century are especially prone to this.
The important point for budget-conscious homeowners is this: if your window frames are structurally sound — no rot, no serious damage, no warping that prevents the window from closing fully — then full replacement is often unnecessary. The heat loss you are experiencing can typically be addressed through targeted, affordable improvements that tackle both draughts and radiant loss at a fraction of the cost of new glazing. With 2026 energy tariffs keeping household bills elevated, even modest savings translate into real money recovered.
Practical tip — before spending anything, run your hand slowly around every window frame on a cold, windy day. Any cold air you feel is money leaving your home that draught-proofing can stop.
How Much Difference Can Budget Window Improvements Actually Make
Budget window improvements genuinely reduce heat loss and can deliver meaningful savings on energy bills — the question is setting realistic expectations about how much improvement each measure provides.
Draught-proofing alone, according to the Energy Saving Trust, can save a typical household between £45 and £65 per year. That figure may sound modest, but for a product costing £3 to £10 per window to apply yourself, the payback period is measured in weeks rather than years. When you combine draught-proofing with secondary glazing film and thermal curtains, the compounding effect becomes more significant — each layer addresses a slightly different mechanism of heat loss, so the improvements stack rather than overlap.
It helps to think in terms of a hierarchy of effectiveness. Draught-proofing addresses air infiltration — the cold draughts that make a room feel chilly even when the heating is running. Secondary glazing film and internal secondary glazing panels address radiant heat loss through the glass itself. Thermal curtains and blinds address both, acting as a physical barrier to convective draughts at the window surface and reducing radiant loss overnight.
What budget improvements will not do is match the performance of new factory-made double or triple glazing with low-emissivity glass coatings. If your windows are severely deteriorated, draughts are extreme, or the glass itself is cracked, replacement may ultimately be more cost-effective. However, for the majority of older homes with windows that close properly and frames in reasonable condition, budget measures can make a genuinely noticeable difference to comfort and bills.
Practical tip — track your energy meter readings for two weeks before and two weeks after making improvements, comparing equivalent weather periods. This gives you a real-world sense of the saving rather than relying on estimates alone.
Draught-Proofing Your Windows and Why It Should Come First
Draught-proofing is the single most cost-effective improvement available for older windows, and it should always be done before any other measure is considered.
The reason draught-proofing comes first is straightforward. Adding secondary glazing film or thermal curtains over a window that still has gaps and draughts is like putting a jumper on over a shirt with no buttons — the outer layer helps, but the fundamental problem remains. Sealing the gaps first means every subsequent improvement works as intended.
There are several main types of draught-proofing products for windows, each suited to slightly different situations.
- Self-adhesive foam strips are the most accessible and inexpensive option, available from any DIY retailer or online supplier. They compress when the window closes, sealing the gap between the sash or casement and the frame. In 2026, expect to pay approximately £3 to £10 per window depending on the length and quality of the product. Foam strips work well on casement windows that close cleanly but are less effective on windows with irregular gaps.
- Rubber or EPDM compression seals are more durable than foam and maintain their shape better over several years. They are slightly more expensive at approximately £10 to £20 per window, but they outlast foam strips considerably and provide a cleaner seal.
- Brush-pile draught excluders are specifically designed for sash windows. A sash window is one where the glazed panels slide vertically past each other, and foam strips cannot be used here because the compression prevents the sash from sliding correctly. Brush strips are fitted into a groove or channel along the sash runner, allowing the window to move freely while still sealing the gap.
- Silicone sealant is appropriate for fixed gaps between the frame and the surrounding wall, or where old putty has cracked and shrunk away from the glass. This is a permanent application and not suitable for any part of the window that needs to move.
If DIY is not practical, a professional draught-proofing service typically costs £80 to £200 for a whole house in 2026, depending on property size and the number and condition of windows. Look for installers registered with TrustMark, the government-endorsed quality scheme for home improvements, and verify their registration on the TrustMark website before booking.
Practical tip — for sash windows specifically, ask for EPDM or brush-pile products at the point of purchase. Standard foam strips are sold widely but are the wrong product for this window type, and using them will either jam the window or fail to seal it properly.
Secondary Glazing Film — A Low-Cost Option Worth Knowing About
Secondary glazing film is one of the most underrated budget improvements available for older windows, offering a genuine reduction in radiant heat loss for a very modest outlay.
Secondary glazing film is a thin, transparent plastic film applied to the interior face of a window frame using double-sided tape. Once stuck in place, it is heat-shrunk taut using a household hairdryer, creating a clear, wrinkle-free surface with a small insulating air gap between the film and the glass. It is this air gap that does the thermal work — still air is an excellent insulator, and even a few millimetres of trapped air significantly reduces the rate at which warmth radiates through the window.
Reputable products from brands such as 3M are widely available in UK DIY and hardware stores, alongside own-label versions from major retailers. In 2026, a typical window kit costs between £5 and £15, making this one of the most affordable improvements on this list. Application requires no specialist tools and can be completed in around 20 minutes per window.
However, the limitations are worth understanding clearly. The film must be replaced at least annually, as removal for ventilation in warmer months means the tape loses its seal. It can cause a very slight reduction in optical clarity compared to clear glass. It is also not a practical solution for windows that need to be opened regularly during winter, since opening the window breaks the film seal immediately.
Where secondary glazing film works best is on windows in rooms where ventilation is not a pressing concern during the heating season — a north-facing guest bedroom, a rarely-used dining room, or a utility room window are all good candidates.
Practical tip — apply secondary glazing film on a dry day when indoor humidity is low, as damp conditions can prevent the double-sided tape from bonding effectively to the frame and reduce the lifespan of the seal.
Internal Secondary Glazing Panels — A Step Up in Performance
For homeowners who want better performance than film can offer, and who are not in a position to replace their windows entirely, internal secondary glazing panels are the most effective budget-to-mid-range option available.
Internal secondary glazing involves fitting a separate panel — made from acrylic, polycarbonate, or glass — inside the existing window reveal on the room side. The gap between the original window and the secondary panel creates an insulating buffer that significantly reduces both heat loss and noise. Unlike film, these panels are designed to be removed for cleaning and ventilation and do not need replacing each year.
DIY systems using magnetic fixing strips or click-in polycarbonate panels are widely available in 2026, with costs ranging from approximately £30 to £80 per window for a self-fitting kit. These are particularly suitable for standard-sized windows and can be cut to size at home with basic tools. Professionally installed secondary glazing — using thicker acrylic or real glass with timber or aluminium subframes — costs considerably more at approximately £150 to £400 per window depending on size and specification, but delivers a higher level of finish and thermal performance.
Secondary glazing is particularly relevant for homeowners in conservation areas or those living in listed buildings, where planning restrictions may prevent the installation of replacement double-glazed units in the original openings. If your property is listed or sits within a conservation area, always contact your local planning authority before fitting any secondary glazing — even internal systems can sometimes require consent, though this varies by local authority and the specific nature of the listing.
Practical tip — when measuring for a DIY secondary glazing kit, measure the reveal depth (the distance from the glass surface to the inner face of the wall) as well as the width and height. You need enough reveal depth to accommodate the panel without it fouling the window furniture or handle.
Thermal Curtains, Blinds, and Shutters — What the Data Says
Even after draught-proofing and secondary glazing, a significant proportion of heat loss through windows occurs at night when the glass is cold and the indoor-to-outdoor temperature difference is at its greatest. Thermal curtains and blinds address this directly.
Heavy, well-fitted curtains with a thermal or blackout lining act as an additional barrier between the room and the cold glass, reducing both radiant and convective heat loss. The Energy Saving Trust notes that drawing curtains at dusk reduces heat loss through windows noticeably, with the effect greatest on windows facing north or east. For curtains to work effectively, however, the fit matters as much as the fabric. Curtains that do not reach the floor, that allow cold air to flow underneath, or that leave gaps at the sides where the track finishes short of the wall will underperform compared to curtains fitted close to the wall on all sides.
The most effective arrangement is ceiling-to-floor curtains hung from a pelmet or track that extends to the wall on each side, with a slight overlap onto the wall to prevent cold air circulation at the edges. A pelmet — a box or shelf mounted above the curtain track — is particularly useful as it stops warm room air from circulating behind the curtain and cooling against the glass.
Honeycomb blinds (also described as cellular blinds) are a practical alternative where curtains are impractical, such as in bathrooms, kitchens, or on staircase windows. They trap air in their honeycomb-shaped cells, providing insulation without the bulk of curtains. Good-quality honeycomb blinds cost approximately £40 to £120 per window in 2026.
At the higher end of this category, internal window shutters — solid timber or composite panels fitted inside the window reveal — combine meaningful draught reduction with substantial thermal benefit. Professionally installed internal shutters typically cost £200 to £600 per window in 2026 and represent a long-term investment rather than a quick fix, but they add to the appearance of a room as well as its warmth.
Practical tip — if full thermal curtains are outside your budget, a good thermal lining sewn or clipped onto existing curtains achieves most of the benefit at a fraction of the cost of buying new curtains entirely.
Comparing the Options — Costs, Savings, and Effort at a Glance
The table below brings together the main window improvement options, their 2026 costs, estimated savings, and key characteristics. Savings figures are estimates based on Energy Saving Trust guidance and will vary significantly depending on property type, the number of windows being treated, current energy tariff, and how draughty the windows were before treatment.
| Method | Approximate DIY Cost (2026) | Approximate Installed Cost (2026) | Estimated Annual Saving | Effectiveness | Reversible |
|---|---|---|---|---|---|
| Foam draught strips (DIY) | £3–£10 per window | N/A | Part of £45–£65 overall draught-proofing saving | Good for casement windows; not for sash | Yes |
| Rubber or EPDM compression seals (DIY) | £10–£20 per window | N/A | Part of £45–£65 overall draught-proofing saving | Very good; more durable than foam | Yes |
| Professional whole-house draught-proofing | DIY only | £80–£200 whole house | £45–£65 per year (Energy Saving Trust estimate) | Very good; professional finish | Yes |
| Secondary glazing film (DIY) | £5–£15 per window | N/A | Low to moderate (complements draught-proofing) | Moderate; reduces radiant loss | Yes (seasonal) |
| DIY secondary glazing panels (magnetic or polycarbonate) | £30–£80 per window | N/A | Moderate; noticeable comfort improvement | Good thermal and acoustic benefit | Yes |
| Professionally installed secondary glazing | N/A | £150–£400 per window | Good; approaches basic double glazing performance | Very good thermal and acoustic benefit | Yes |
| Thermal curtains (DIY fitting) | £30–£100+ per window | N/A | Moderate; most effective overnight | Good when well-fitted and floor-length | Yes |
| Internal window shutters (installed) | N/A | £200–£600 per window | Good; long-term investment | Very good draught and thermal benefit | Yes |
The clearest takeaway from this comparison is that draught-proofing offers the best return per pound of any measure on the list. If your budget is limited, prioritise sealing gaps before anything else. Once draughts are addressed, secondary glazing film and thermal curtains provide the most cost-effective next steps before moving to more substantial investments.
Practical tip — total up the cost of treating all affected windows in your home using the figures above. A whole-house draught-proofing and film programme for a three-bedroom semi-detached home with ten windows could realistically cost under £150 as a DIY project — a figure that pays back within two to three heating seasons.
How to Choose the Right Approach for Your Windows — A Step-by-Step Guide
Choosing the right combination of measures depends on your specific windows, your property type, your budget, and how the rooms are used. Follow these steps to build the right plan for your home.
- Assess your windows honestly. On a cold, windy day, hold a lit incense stick or a damp hand near window frames, sash runners, and the junction between frame and wall. Moving air indicates a draught that needs sealing. Also look for condensation between double-glazed panes (which signals a failed unit seal), cracked or missing putty, and gaps where the frame meets the surrounding wall. Document which windows are worst affected so you can prioritise spending.
- Establish your budget clearly. Under £50 limits you to foam or EPDM draught strips and secondary glazing film across a handful of priority windows. A budget of £50 to £200 opens up whole-house draught-proofing plus film on all windows. With £200 to £500 you can add DIY secondary glazing panels on the coldest or most-used rooms. Above £500, professionally installed secondary glazing or thermal shutters become realistic.
- Check conservation area and listed building status before buying anything. If your property is listed or in a conservation area, contact your local planning authority before fitting secondary glazing. While draught-proofing strips and thermal curtains are generally unaffected, secondary glazing panels can sometimes require consent. Getting this wrong wastes money and may require remediation.
- Prioritise draught-proofing first. Whatever your total budget, spend on sealing gaps before anything else. This delivers the best return per pound of any window improvement and makes every subsequent measure more effective by ensuring cold air infiltration is addressed at source.
- Choose a secondary layer suited to how each room is used. Secondary glazing film works well for rarely-opened windows in low-traffic rooms. Removable panels suit rooms where occasional ventilation is needed but thermal performance is important. Thermal curtains complement every other measure and are particularly effective overnight. Fit them wherever practical, regardless of what other measures you have used.
- Monitor your results. Note your energy meter reading on the day you complete improvements, then check again after four weeks of comparable weather. Use a basic room thermometer to check whether persistent cold spots near windows have improved. This step is practical rather than optional — it tells you whether the measures have worked and where you might still have gaps.
guide to secondary glazing for listed buildings and conservation areas
Practical tip — tackle the coldest room in the house first. You will notice the difference immediately, which makes it easier to judge whether the approach is working before committing to the full house.
Are There Any Grants or Funding Available for Window Improvements in 2026
Several UK funding schemes are relevant to window improvements in 2026, though eligibility conditions vary significantly and it is important to understand what each scheme does and does not cover.
The Energy Company Obligation 4 (ECO4) scheme is the main route by which low-income or vulnerable households can access funded energy efficiency improvements, including window upgrades in some circumstances. ECO4 is delivered through energy suppliers and focuses on homes with low Energy Performance Certificate (EPC) ratings. Full window replacement can in some cases be funded under ECO4 where it forms part of a broader energy efficiency package. The best starting point for eligibility is the Simple Energy Advice service, operated under government guidance, which assesses your household’s likely qualification across multiple schemes. full guide to ECO4 eligibility and how to apply
The Great British Insulation Scheme (GBIS) is primarily focused on insulation measures such as loft, wall, and underfloor insulation, but in some circumstances draught-proofing can be included as part of a wider package of improvements. Homeowners should contact a GBIS-participating installer directly to ask whether draught-proofing can be included alongside other funded work on their property.
The Boiler Upgrade Scheme (BUS) does not fund window improvements directly. However, it is worth noting that improving window efficiency before installing an air source heat pump — which requires MCS-accredited installation — can improve your home’s overall heat loss calculation and contribute to a better system design and potentially a more efficient heat pump specification.
Homeowners in Wales should investigate the Nest scheme, administered by Warm Wales, which provides free home energy improvements to eligible households and can cover a broader range of measures than England-only programmes. Homeowners in Scotland should contact Home Energy Scotland, which provides impartial advice and referrals to funded schemes including some that cover window draught-proofing and secondary glazing in eligible properties. devolved home energy schemes — Wales and Scotland guide
Private renters face a more complex picture. Most grant schemes require applications from the property owner, meaning tenants cannot access funding directly. However, landlords letting properties in England are subject to Minimum Energy Efficiency Standards (MEES), which set a minimum EPC rating of E for most tenancies. Where a property falls below this threshold, landlords may be obliged to make improvements. Tenants in cold, draughty properties should raise the issue with their landlord and, if necessary, contact their local council’s private rented sector team for enforcement advice. tenant rights and energy efficiency — what renters can demand
Always use the Simple Energy Advice service or speak directly with your energy supplier before assuming you do not qualify for funded support. Eligibility rules are updated regularly, and schemes that were unavailable to your household previously may have changed in your favour.
When Budget Improvements Are Not Enough — Knowing When to Replace
Budget improvements deliver real results, but they have limits. There are circumstances in which full window replacement is genuinely the more cost-effective long-term choice, and homeowners deserve honest guidance on when that threshold is reached.
If a window frame has significant timber rot that compromises its structural integrity, draught-proofing will not cure the underlying decay. Rotting frames allow moisture ingress as well as draughts, and the ongoing cost of maintenance and heat loss typically justifies replacement. Similarly, if double-glazed units have failed seals — indicated by persistent condensation or misting between the panes — the unit itself needs replacing, though in many cases the frame can be retained and only the glass unit exchanged, which is considerably cheaper than full replacement.
Homes with metal-framed windows from the mid-twentieth century — often found in interwar and post-war properties — present a particular challenge. The frames conduct heat very effectively through thermal bridging, and while draught-proofing helps, the frame material itself limits how much improvement is possible without secondary glazing or replacement.
When obtaining quotes for full window replacement, look for installers registered with FENSA or CERTASS, which are the competent person schemes for window and door replacement in England and Wales. These registrations confirm that the installer can self-certify the work meets Building Regulations, saving you the cost of a separate building control application. Always obtain at least three quotes before committing. how to choose a window installer — accreditation and what to check
Practical tip — if you are weighing up budget improvements against full replacement, ask a FENSA-registered installer for a written quote and then compare the total cost against the combined cost of the budget measures in this article. For windows in sound condition, the budget approach almost always offers better value. For windows in poor structural condition, the calculation frequently tips the other way.
Improving the energy efficiency of older windows does not have to mean spending thousands. For the price of a few draught strips, a roll of secondary glazing film, and a pair of thermal curtains, most homeowners with older windows can make a genuinely meaningful improvement to their home’s warmth and their energy bills this winter. Start with the gaps, layer up from there, and be clear-eyed about what each measure can and cannot achieve — that combination of action and realism is the most reliable route to a warmer home at the lowest possible cost.
Frequently Asked Questions
how much does it cost to draught proof windows yourself in the UK?
DIY draught-proofing materials typically cost £3 to £10 per window depending on whether you use self-adhesive foam strips, brush pile strips, or silicone sealant. For a typical three-bedroom home with eight to ten windows, the total materials cost is usually between £30 and £80. The Energy Saving Trust estimates draught-proofing windows and doors can save a household around £45 to £65 a year on energy bills, meaning the outlay can pay back within a single heating season.
does secondary glazing film actually work on old windows?
Secondary glazing film creates a thin air gap between the film and the glass, which reduces convective and radiant heat loss measurably. Independent testing suggests it can cut heat loss through a single-glazed window by 35 to 45 percent, bringing the effective U-value closer to 3.0 W/m²K from the single-glazed baseline of around 5.0 W/m²K. Kits covering a standard window cost roughly £8 to £15, making this one of the most cost-effective improvements available before committing to permanent secondary glazing or full replacement.
can I get any grants to help improve old windows in the UK in 2026?
Full window replacement may qualify for support under the Great British Insulation Scheme if your home is in council tax bands A to D and has a poor EPC rating, with some households receiving contributions worth hundreds of pounds toward glazing upgrades. The Warm Homes Plan, being rolled out from 2026, also targets heat loss improvements for lower-income and fuel-poor households, potentially covering window draught-proofing as part of a broader retrofit package. Contact your local energy advice centre or check the government's Simple Energy Advice service to confirm current eligibility, as scheme availability varies by local authority.
what is the cheapest alternative to replacing single glazed windows?
The cheapest alternative is a layered approach combining draught-proofing strips, secondary glazing film, and thermal curtains, which together can cost under £50 per window and reduce heat loss by more than half. If you want a more durable upgrade without full replacement, magnetic or clip-in acrylic secondary glazing panels cost £50 to £150 per window installed and can achieve U-values of around 1.8 to 2.0 W/m²K — close to entry-level double glazing. These options are especially worthwhile in listed buildings or conservation areas where planning restrictions may prevent window replacement outright.
how do I know if my old windows are causing high heating bills?
A simple test is to hold a lit incense stick or a damp hand near the window frame edges, sash runners, and the join between frame and wall on a cold or windy day — any movement of smoke or sensation of cold air indicates draught infiltration. You can also check your home's EPC rating, which assigns a score to window glazing and flags single-glazed windows as a significant contributor to a low energy rating. Homes with single glazing and an EPC of E, F, or G are likely losing a substantial portion of heat through windows, and the Energy Saving Trust estimates this can equate to £100 or more in unnecessary heating costs each winter.
