How to Keep Your Home Cool in a Heatwave Using Blinds, Curtains & Shutters

Heatwave window treatments are one of the most effective tools you have right now.With temperatures climbing across Hertfordshire this week and the Met Office issuing amber heat alerts, keeping the house cool has become the priority in many homes right now. Fans help. Opening windows at night helps. But the single most effective thing you can do during daylight hours is control what comes through your windows.

Up to 87% of a home’s heat gain during a heatwave enters through the glass. Your window treatments are your first line of defence, and the right choice makes a significant difference. The wrong choice, or no choice at all, means your home acts like a greenhouse from mid-morning onwards.

The key insight: internal window coverings can block up to 40% of solar heat gain. Combine the right product with the right fabric and a well-fitted installation, and you can keep rooms noticeably cooler without touching an air conditioning unit.

This guide covers which products work best, how they compare, and what to look for in fabric and fit.

Why Your Windows Are the Problem

Most people assume the solution to a hot house is airflow. In fact, during a heatwave, opening windows during the hottest part of the day actively makes things worse. If it is 30°C outside, you are simply inviting that air in.

The real culprit is solar gain: the process by which sunlight passes through glass and converts to heat inside your room. South- and west-facing windows are the worst offenders, receiving the most direct sun between late morning and early evening.

According to Houzz’s guide to cooling window treatments, there are three ways to block sunlight:

• Externally (shutters, pergolas, awnings): can block up to 100% of heat before it reaches the glass
• Mid-pane (integral glazing blinds): can block 60–80% of heat
• Internally (blinds, curtains): blocks up to 40% of heat

Internal window treatments are the most accessible and most popular option for existing homes. The key is choosing the right type.

The Best Blinds for Keeping Heat Out

Not all blinds are equal when it comes to heat control. Here is how the main types compare.

Roller Blinds with Solar or Blackout Fabric

Roller blinds are the most versatile option for heat management. The fabric choice is everything.

• Solar fabrics (also called screen fabrics) are woven with a specific openness factor, typically 1–5%. They reflect a significant proportion of solar radiation while still allowing a degree of natural light through. Ideal for rooms where you want to reduce glare and heat without losing the view.
• Blackout fabrics with a white or light-coloured reverse will reflect rather than absorb heat. The colour on the room-facing side matters less than the colour on the window-facing side; always opt for a pale reverse if heat reduction is a priority.
• Perfect-fit roller blinds, which clip directly into the window frame with no gaps around the edges, are particularly effective because they eliminate the air channels that allow warm air to circulate between the blind and the glass.

Roman Blinds

Made-to-measure Roman blinds can be highly effective when lined with a thermal or blackout lining. The fabric stacks flat against the window when raised, and when down, a well-fitted Roman sits snugly within or just beyond the recess, reducing the gap through which warm air can travel. Choose a light-coloured fabric or a white thermal interlining for maximum reflectivity.

Pleated and Cellular Blinds

Honeycomb or cellular pleated blinds are arguably the most technically effective internal option for heat control. Their unique structure creates pockets of trapped air between the fabric layers, forming an insulating barrier at the window. The same cellular structure that keeps warmth in during winter keeps heat out in summer. Our pleated blinds are made to measure for even awkward or shaped windows, including conservatories where solar gain is most intense.

Venetian Blinds

Venetian blinds offer excellent adjustability. By angling the louvres upward, you can deflect direct sunlight toward the ceiling rather than into the room, reducing glare and heat while maintaining some airflow. Aluminium Venetians with a white or silver finish reflect heat more effectively than wood or faux-wood versions, though all types offer useful control.

Shutters: The Most Effective Internal Solution

For year-round temperature control and versatility, plantation shutters are hard to beat. The adjustable louvres give you precise control over how much direct sunlight enters the room, and when fully closed, the solid panels create a genuine barrier between the glass and your living space.

It is worth being precise about where shutters excel, though. Their real strength is louvre adjustability and year-round performance: in winter, closed shutters reduce heat loss significantly. In summer, the story is more nuanced. When louvres are angled open for airflow, shutters reduce solar heat gain by around 30–35%. Solar screen roller blinds and cellular honeycomb blinds can outperform that figure for pure heat blocking. Where shutters win is the combination of light control, ventilation, and insulation in a single, permanent fitting.

Worth knowing: Full-height shutters with a mid-rail allow you to operate the top and bottom panels independently. Close the upper louvres to block the high summer sun while keeping the lower panel open for ventilation. It is a level of control that no blind or curtain can match.

Our plantation shutters are available in a range of louvre widths, with wider louvres (89mm or 114mm) offering greater light and airflow control when partially open. A UV-resistant paint or stain finish also prevents the shutter from fading or warping in prolonged sun exposure.

What to Do with Curtains in a Heatwave

Curtains are often overlooked for heat control, but the right curtains with the right lining can be genuinely effective. The Guardian’s sustainability researcher Stuart Walker recommends drawing thermal curtains during the hottest part of the day, noting they are “most effective when they feature a pelmet to trap air” at the top of the window.

A pelmet or a close-fitting track that sits tight to the wall prevents the warm air that builds up between the curtain and the glass from spilling into the room. Without one, even well-lined curtains can create a convection effect that draws warm air downward into the space.

Lining choices that make a difference

• Thermal lining: adds a layer of insulating fabric that slows heat transfer through the curtain
• Blackout lining: blocks light almost entirely; effective for bedrooms during afternoon sun
• White or pale reverse: regardless of lining type, a light-coloured fabric on the window-facing side reflects more solar radiation than a dark one

Fabric weight and weave

Heavier, tightly woven fabrics perform better than lightweight sheers for heat blocking. That said, sheer voiles still have a role to play: layering a voile with a lined curtain gives you flexibility throughout the day. The voile filters light and reduces glare while the lined curtain can be pulled across during peak sun hours.

Our made-to-measure curtains are available with a full range of lining options. If you are not sure which combination suits your room, that is exactly what our free consultations are designed to help with.

Motorised Blinds: The Smart Heatwave Solution

One of the most practical upgrades for managing summer heat is motorisation. Motorised blinds allow you to schedule your window treatments to close automatically during the hottest part of the day, even when you are out of the house.

This matters more than it might seem. The reason most homes overheat is not because the blinds are ineffective; it is because nobody remembers to close them before 10am on a south-facing window. By the time you notice the room is uncomfortably warm, the heat has already built up and is much harder to shift.

With a motorised system connected to a smart home hub or a simple timer, your blinds close at 9am and reopen at 6pm without any manual intervention. Come home to a cool house rather than a room that has been baking all day.

Particularly useful for:

• South- and west-facing rooms that receive prolonged direct sun
• Conservatories and orangeries where solar gain is most intense
• Households where windows are often left unattended during the day
• Anyone who wants consistent temperature management without the daily routine

Motorisation also works well in combination with other window treatments. Motorised roller blinds paired with a fixed shutter, for example, give you automated daytime shading and full manual control in the evenings.

Quick Comparison: Which Window Treatment Works Best?

The most effective approach in any room is to layer treatments: a blind for daytime heat control and a lined curtain for the evenings and early mornings. Made-to-measure fitting is critical; gaps around the edges of any treatment reduce its effectiveness significantly.

Get the Right Solution for Your Home

The right window treatment depends on the orientation of your windows, the size of the room, how you use the space, and your longer-term goals. A south-facing bedroom calls for a different solution than a west-facing kitchen, and a conservatory needs a different approach altogether.

We offer free, no-obligation consultations at our Welwyn Garden City showroom and in your home across Hertfordshire, including St Albans, Harpenden, Hertford, Hatfield, Potters Bar, Ware, and Stevenage. If you are dealing with an overheating room right now and want a practical, well-fitted solution, get in touch with us today or book a consultation online. We will help you find the right product, fabric, and fit for every window in your home.