How Much Heat Do Old Windows Lose in Winter?

Winter is often when homeowners really notice how much heat their windows are losing. Rooms cool down faster, heating stays on longer, and certain areas of the home feel colder than others. While walls and roofs play a role, older or poorly performing windows are one of the most common sources of heat loss.

At MK Doors & Windows, we regularly assess windows across Milton Keynes to identify where heat is escaping and whether repair, glass replacement, or a full upgrade is the most sensible solution. This guide explains how heat loss happens and what you can do about it.

How Heat Escapes Through Windows

Heat loss through the glass

Single glazing and older double glazed units allow significantly more heat to pass through than modern glass. Even if the window looks intact, the insulating performance may be well below current standards.

Heat loss around the frame

Small gaps caused by worn seals, loose hinges, or misalignment allow cold outside air to enter while warm indoor air escapes. These draughts can have a bigger impact than people realise.

Failed sealed units

When the seal in a double glazed unit breaks down, the trapped air or gas is lost. This reduces insulation and often causes the inner pane to feel noticeably colder.

Signs Your Windows Are Losing Heat

• Cold draughts near the edges of the window frame.

• Rooms cooling quickly once the heating is turned off.

• Condensation or misting between the glass panes.

• Windows that feel much colder than surrounding walls.

• Rattling or stiff handles when opening and closing.

What Can Be Done to Reduce Heat Loss?

Window servicing and repairs

If the frame is in good condition, servicing the window can significantly improve warmth. This often includes replacing seals, adjusting hinges, and ensuring the window closes tightly.

These issues are commonly resolved through our Window and Door Repairs service.

Sealed unit replacement

If the glass unit has failed but the frame is sound, replacing only the sealed unit is often the most cost effective fix. This restores insulation and clarity without the disruption of a full replacement.

Find out more on our Sealed Unit Replacements page.

Secondary glazing

For older properties or homes where window replacement is not suitable, secondary glazing adds an extra internal pane that improves insulation and reduces noise. It is especially effective during winter.

More information is available on our Secondary Glazing page.

New window installation

If frames are damaged, very old, or you want the highest level of energy efficiency, replacing the windows may be the best long-term option.

You can explore modern options on our New Window Installation and uPVC Windows pages.

Repair or Replace? How to Decide

If your windows are generally in good condition and the issue is draughts or failed glass, repairs or sealed unit replacement are usually the best starting point. If multiple windows are inefficient or frames are deteriorating, replacement may offer better long-term value.

Our team provides honest advice based on what will actually improve warmth and comfort, not what costs the most.

Book a Winter Window Assessment in Milton Keynes

If you are concerned about heat loss through your windows this winter, we can assess the condition of your frames and glazing and recommend the most practical solution.

To arrange a free quote, visit our Contact Us page or view examples of recent work in our Gallery.