How to Cut Heating Bills by 30% Without Replacing Your Windows

Published 11 August 2026 · Sash Window Draught Proofing

Replacing original sash windows is not the only way to improve thermal efficiency. In many Victorian and Georgian properties, professional sash window draught proofing and carefully specified secondary glazing for sash windows can reduce heat loss while preserving original timber, glass and architectural detail.

Draught proofing can reduce window-related heat loss by up to 30%, while secondary glazing can reduce heat loss through the window area by up to 70%. These figures are not guaranteed reductions in the total household energy bill. Actual savings depend on the size and condition of the windows, heating controls, property construction and energy use. However, the measures can provide a measurable return on investment without replacing the windows.

Why Original Sash Windows Lose Heat

Traditional sash windows generally lose heat in two different ways:

1. Air leakage: Cold air enters through gaps around the sashes, meeting rails, staff beads and frame.
2. Heat transfer through the glass and timber: Single glazing has limited insulating performance, allowing warmth to pass through the window.

A draughty window can feel uncomfortable even when its glass is relatively sound. In practice, stopping uncontrolled airflow is often the most cost-effective first step for homeowners considering draught proofing period properties.

Secondary glazing addresses the second problem by adding a separate internal pane. This creates a still-air gap between the original window and the new glazing, reducing heat transfer and limiting cold downdraughts.

U-Values Explained

A U-value measures how quickly heat passes through a building element. It is expressed in watts per square metre Kelvin, or W/m²K.

• A high U-value indicates greater heat loss.
• A low U-value indicates better insulation.
• The U-value of the complete window depends on the glass, frame, seals and installation.

Typical single-glazed sash windows may have U-values in the region of 5.0–6.0 W/m²K. Adding secondary glazing can reduce the effective U-value to approximately 1.8–2.8 W/m²K, depending on the system, glass specification and air gap.

Modern double glazing may achieve lower U-values. However, full replacement can involve substantial cost, changes to the original appearance and restrictions in conservation areas or listed buildings. Secondary glazing provides a way to improve performance while retaining the existing window.

Air Leakage: The Highest-ROI Starting Point

Draught proofing does not make single glazing behave like modern insulated glass. Its main purpose is to reduce gaps and uncontrolled air movement.

Professional draught proofing typically involves:

• Installing discreet brush seals to the meeting rails and sash edges.
• Replacing worn or missing staff beads.
• Sealing gaps around the frame where appropriate.
• Checking the alignment and movement of the sashes.
• Repairing damaged putty, joints or timber before sealing.
• Inspecting sash cords, pulleys and hardware during the same visit.

The result should be a window that remains functional but closes more tightly. The original appearance is largely preserved, and the intervention is normally reversible.

Professional Draught Proofing: Cost and Payback

A realistic starting budget for professional sash window draught proofing is:

• £150–£300 per window
• More for large windows, difficult access or restoration work
• Additional repairs, sash cord replacement or timber treatment may increase the quotation

The expected payback period is approximately two years in suitable properties, although the precise period depends on heating demand and energy prices.

A simple calculation can help assess the investment:

> Payback period = installation cost ÷ annual energy saving

For example, if draught proofing costs £240 per window and produces an estimated annual saving of £120, the simple payback period is two years. After that point, the improvement continues to reduce heat loss and improve comfort.

This calculation should be treated as an estimate rather than a guarantee. A survey is needed to identify which windows are leaking most and whether repair work is required first.

Read our cost of draught proofing guide for more information about pricing factors.

Secondary Glazing for Sash Windows

Secondary glazing is an independent glazed panel installed on the room side of the original window. It does not require the existing sash to be removed.

Depending on the window and room, systems may be:

• Vertical sliding, to complement sash operation.
• Hinged, where access and ventilation are priorities.
• Fixed, where maximum simplicity and security are required.
• Magnetically removable, where reversibility is particularly important.

A bespoke system can be designed around existing glazing bars, shutters, cornices and narrow reveals. It is particularly suitable for Grade II listed buildings and homes in Conservation Areas because the external elevation remains unchanged.

Secondary glazing can provide:

• Improved thermal efficiency.
• Lower U-values.
• Reduced cold spots and downdraughts.
• Better acoustic performance.
• Additional security.
• Less condensation risk when ventilation and detailing are correctly managed.

Secondary Glazing: Cost and Payback

A typical budget for premium secondary glazing is:

• £400–£800 per window
• Acoustic glass, complex shapes and large bays may cost more
• Surveying, bespoke manufacture and installation are normally included in a detailed quotation

The expected ROI period is approximately five years, subject to the property's heat-loss profile and household energy use.

Secondary glazing usually requires a higher initial investment than draught proofing. Its financial case is strongest where:

• The property has many large single-glazed windows.
• Rooms are difficult to heat.
• The home is exposed to wind or traffic noise.
• The original windows cannot be replaced.
• The owner intends to remain in the property for several years.

The financial benefit is not limited to fuel savings. A warmer, quieter and more comfortable property may also be easier to let or sell, while reversible improvements help protect heritage value.

Draught Proofing or Secondary Glazing?

Choose Draught Proofing If…

• Your main problem is noticeable cold air around the sashes.
• You want the lowest initial investment.
• The existing windows are structurally sound.
• You want minimal visual change.
• You are looking for a short installation period and a potential two-year payback.

Choose Secondary Glazing If…

• Your priority is maximum thermal improvement.
• The windows are single glazed and rooms remain cold.
• The property faces a busy road, railway or flight path.
• You want a reduction in both heat loss and external noise.
• You are prepared for a larger investment with an approximately five-year payback.

Combine Both If…

In many period properties, combining the two measures offers the strongest result. Draught proofing reduces air leakage, while secondary glazing improves the insulating performance of the window assembly.

A practical approach is to:

1. Draught proof all frequently used sash windows.
2. Add secondary glazing to bedrooms, living rooms and street-facing elevations.
3. Use acoustic specifications where noise is a major concern.
4. Prioritise the windows with the largest area or most severe draughts.
5. Review the results before upgrading less-used rooms.

How to Reach a 30% Heating-Bill Reduction

Window improvements should form part of a wider energy-efficiency plan. To approach a 30% reduction in heating costs:

• Seal draughts around doors, loft hatches and floorboards.
• Use thermostatic radiator valves correctly.
• Set heating schedules around occupancy.
• Keep internal shutters or thermal curtains closed at night.
• Avoid placing furniture directly over radiators.
• Check that roof, loft and floor insulation are adequate.
• Balance ventilation with airtightness to manage moisture safely.

The biggest savings are generally achieved when a property has substantial uncontrolled air leakage and high heating demand. A well-insulated home with already efficient windows may see a smaller percentage reduction.

For further background on traditional window performance, see Historic Environment Scotland’s guidance on reducing heat loss from sash windows.

Solutions for London Period Properties

The correct specification depends on the building, elevation and local heritage requirements. Homeowners researching secondary glazing in different London areas may find these specialist resources useful:

• Secondary glazing in Kensington and Chelsea for heritage terraces and mansion flats.
• Secondary glazing in Islington and Camden for Georgian and Victorian properties.
• Secondary glazing in Richmond for period homes affected by exposed locations or aircraft noise.
• The guides to secondary glazing in Hampstead and Belsize Park and Richmond and Twickenham.
• Secondary glazing in Westminster and Kensington and Chelsea.

You can also compare area-specific information about Kensington secondary glazing and Chelsea secondary glazing.

These resources should not replace a property-specific survey. Window proportions, reveal depth, listed status and existing condition all affect the recommended system.

A Sensible Investment Strategy

For many homeowners, the most financially sensible sequence is:

1. Survey: Identify air leakage, failed putty, damaged timber and operational problems.
2. Repair: Restore the window sufficiently for reliable operation.
3. Draught proof: Address the highest-impact gaps first.
4. Add secondary glazing selectively: Prioritise rooms with the greatest heat loss or noise exposure.
5. Review performance: Compare comfort and heating use across the following season.

This staged approach avoids paying for premium glazing where a lower-cost intervention may be sufficient. It also preserves original windows rather than treating replacement as the default solution.

Frequently Asked Questions

Can draught proofing reduce my heating bill by 30%?

It can reduce window-related heat loss by up to 30% in suitable properties. The effect on the total heating bill depends on how much heat is lost through the windows and how the rest of the property performs.

Can secondary glazing reduce heat loss by 70%?

Secondary glazing can reduce heat loss through the window area by up to 70% when correctly specified and installed. The percentage reduction in the total household bill will usually be lower.

Does secondary glazing require planning permission?

Because it is installed internally and does not alter the external elevation, secondary glazing is often acceptable in Conservation Areas. Listed buildings may still require a property-specific review, and listed building consent should not be assumed to be unnecessary.

Is draught proofing reversible?

Professional draught proofing is designed to preserve the original window and can generally be reversed. Any timber repairs or replacement components should be discussed before work begins.

Arrange a Window Assessment

A professional survey can establish whether your home is best suited to draught proofing, secondary glazing or a combination of both. Sash Window Draught Proofing provides heritage-sensitive solutions for London period properties, including Grade II listed buildings and homes in Conservation Areas.

Explore our secondary glazing versus draught proofing guide, review our secondary glazing service, or contact us for a tailored quotation.

The objective is straightforward: reduce heat loss, improve comfort and protect the original windows that give your property its character.