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How to insulate windows

How to insulate windows - featured. Close up of person's hands putting sealing tape at the bottom of a window frame

Say goodbye to draughts with our easy-to-follow tips

If you’re blasting your heating but are still struggling to feel the full benefit, it may be worth looking at how to insulate your windows.

With the cost of energy high, and staying high, all of us have one eye on the thermostat and the other on our energy bills, so it can be dispiriting to know that a significant proportion of that expensive heating is going, literally, straight out the window. Even heating smaller, more local areas with an electric heater may not have much of an impact. And installing new windows probably isn’t an option for everyone right now either – new double glazing for an average three-bedroom house could be expected to cost around £11,000.

Luckily, there are things you can do to improve your window insulation, without breaking the bank completely. From thermal curtains to weather-sealing tape and secondary glazing, there are pocket-friendly alternatives to replacing all your windows.

If learning the best ways to keep your house warm is high on your to-do list, read on for our expert tips and stay cosy with newly insulated windows.

Should I insulate my windows?

You probably already know if your windows could benefit from extra insulation – damaged or missing sealing strips are a giveaway, as is fogging or condensation, and compromised glass. Still not sure? Oliver Creevy, managing director and co-founder of Insulation Advisor UK, told us of a couple of tests that will help you identify leaks, whether you’ve got sash windows or casement windows, UPVC or wooden frames, single-glazed or double-glazed:

  1. The Hand Test: “Hold your hand near the edges and corners of the window frame on a windy day. A noticeable coolness indicates a draught.”
  2. The Flame Test: “Light a match or incense stick and hold it near the window frame. If the flame flickers, it suggests a draught. Warning – be very cautious.”

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Can I insulate my windows myself?

There are things you can do yourself to try and improve matters when it comes to draughty windows. Try one, or more, of the following to keep the cold at bay.

Draught excluder tape – also known as ‘weather tape’, this is an easy-to-use, self-adhesive foam tape that you can employ to close any gaps in the seal between the window and its frame. Simply cut the tape to size and apply it to a clean (and dry) frame. It’s cheap and effective and should be your first port of call when it comes to fixing draughts.

Thermal curtains – keeping your curtains and blinds open while the sun shines can really help to heat up a room, and then closing them once it’s dark can help reduce chills, at least so long as you fit some good quality, thick curtains or blinds. We rounded up the best thermal curtains you can buy and highly recommend the beautiful Morris & Co Pimpernel Thermal Eyelet Curtains. If you aren’t keen to change your existing curtains then it’s relatively straightforward to sew a thermal layer into them, if you’re handy with a needle and thread. Oliver also suggested simply doubling up: “Layer your window treatments to trap heat. Combine thermal curtains with cellular shades for ultimate insulation power.”

Draught stopper – if you have gaps at the bottom of your doors or windows then you can use a fixed, solid draught excluder to prevent the cold air from entering the house. These are usually made from aluminium or UPVC and can simply be pushed into the frame, you just need to measure up and choose the right size. For patio doors or front doors with a bottom draught, you can also buy fabric draught excluders that can be in the form of anything from a no-nonsense brush to a novelty schnauzer.

Window insulation kit – if you have single glazing, or think you’re losing the majority of heat through the pane itself, then a window insulation kit might be a good temporary, budget solution. This is basically a transparent film that you fit over windows to trap draughts and will work well for a season or a cold snap. It also has the benefit of reducing noise and may even help tackle condensation or mould. Oliver advises that preparation is key to a successful installation: “Clean your windows meticulously with a glass cleaner for a flawless film application and opt for a microfibre cloth to avoid scratches.”

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Can I use cling film to insulate my windows?

You may have heard of people using cling film as a DIY insulation hack. But does it work? We asked Jon Bonnar, managing director of Cotswold Energy Group: “Technically, yes, cling film can help reduce energy loss and cut back heating costs. In fact, any airtight material can be used to trap warm air and prevent heat from escaping through your windows.”

How to insulate windows. Hands unrolling cling film against a light blue background

But he also warned us that it’s not going to be a long-term solution by any means: “Cling film is unlikely to last long. It’s also going to be awkward to fit, so you’re unlikely to get a crease-free finish. It might work temporarily, during a cold snap, but you’re much better off buying a window film kit and installing that instead.”

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What about professional window insulation?

Still feeling chilly? It may be time to call in the pros and explore the options for making some longer-term investments in your windows.

  • Window caulking and sealing – To ensure heat can’t be lost between the window frames and panes you can have these professionally sealed. Oliver says, “High-quality caulk will create a long-lasting barrier against draughts and improve energy efficiency.” From around £25-100 per window.
  • Secondary glazing installation – If your single-glazed or double-glazed windows are proving ineffective, you could consider having another panel of glazing installed, rather than replacing the whole window. These can either be fixed or removable and you should expect to pay £300-500 per window.
  • Window replacement options – If you’ve exhausted all other options and have the budget for replacement windows then make sure you do your research and consult professionals for their recommendations. Today, windows are scored on their heat retention and the rate at which heat is lost (U-Value), so look for replacement glazing with a high energy rating and low U-Value. Triple glazing is generally the most efficient but can be prohibitively expensive. You can expect to spend upwards of £11,000 reglazing a whole house, though costs can vary greatly depending on materials and location.

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