Blackout Curtains vs Aircon — What Cools Your Home First?
Blackout curtains and portable air conditioners both appear in “how to cool your bedroom” articles, but they operate on completely different physics. One blocks solar heat from entering. The other removes heat already in the room. Understanding which problem you have — and when you have both — determines which solution to buy, and in what order. This guide gives you the thermal data and a clear verdict for UK conditions.
Cost & Price — What You Actually Pay
The purchase price gap is large and rarely presented honestly. A pair of blackout curtains for a standard UK bedroom window costs £25–80. A portable air conditioner starts at £240 for a genuine refrigerant unit. The total cost of ownership calculation, however, depends heavily on how hot your summers are and how many nights per year you actually need the room cooled.
| Cost factor | Blackout curtains | Portable AC |
|---|---|---|
| Purchase price (budget) | £25–40 | £240 |
| Purchase price (mid-range) | £50–80 | £350–449 |
| Installation | £0 (DIY pole) | £0 (self-install) |
| Power draw | 0 W | 700–1,000 W |
| Running cost per hour | 0p | 17–24p |
| 3-month summer cost (8 hrs/night)* | £0 | £122–173 |
| 5-year total cost | £25–80 | £800–1,100 |
| Useful life | 5–10 years | 5–8 years |
*Running costs at 24p/kWh (UK average 2026). 3 months = 90 nights. Portable AC at 850W average (Pro Breeze 7,000 BTU at ~750W; MeacoCool 9,000 BTU at ~930W).
The 5-year total cost gap is striking, but it only holds if you are comparing like-for-like cooling outcomes. Curtains are a passive measure — they reduce peak room temperature by 2–4°C in favourable conditions. A portable AC drops room temperature by 8–12°C and holds it there. If your bedroom reaches 32°C during a heatwave, curtains that bring it to 28°C are insufficient for sleep. An AC that brings it to 21°C is not.
Hidden costs of a portable AC: a window seal kit (around £14.99) is needed to seal the gap around the exhaust hose. A replacement hose (around £14.95) extends placement options. A smart plug (around £15.97) lets you pre-cool the room on a schedule. Budget an additional £40–50 in accessories. Blackout curtains have no hidden costs.
Problems & Drawbacks — The Real Complaints
Blackout curtain problem 1: they address the wrong heat source after a multi-day heatwave
During a UK heatwave, the primary problem after day two or three is not solar gain through windows — it is the thermal mass of the building itself. Brick, concrete, and plasterboard absorb heat throughout the day and radiate it inward through the night. By the third consecutive day of 32°C+ temperatures, a UK bedroom wall can be 28°C on its interior surface at midnight. Blackout curtains address solar gain through glass; they do nothing about radiant heat from walls, ceiling, or floor. A room that has been baking for three days needs heat actively extracted, not just prevented from entering via one surface.
Blackout curtain problem 2: north-facing rooms gain almost nothing from them
Direct solar radiation through a window requires the sun to be shining on that window. North-facing rooms in the UK receive minimal direct sun between April and September — the solar gain from a north-facing window at 51°N latitude is a fraction of a south or west-facing window. If your bedroom faces north, blackout curtains provide thermal benefit primarily by acting as an insulating layer (reducing conductive heat transfer through the glass), not by blocking radiation. That effect is real but modest — typically less than 1°C of temperature difference. The thermal benefit you read about in curtain marketing is largely a south/west-facing-window phenomenon.
Blackout curtain problem 3: they block the only passive cooling mechanism available at night
The most effective free cooling strategy in a UK summer is night purge ventilation — opening windows once outdoor temperature drops below indoor temperature (typically after 10pm) to flush the room's stored heat with cooler outdoor air. Blackout curtains drawn across a closed window prevent this. Many people keep curtains closed at night for privacy and darkness, inadvertently blocking the ventilation path. Blackout roller blinds that retract to allow an open window behind them are one solution; heavy floor-length curtains are the worst configuration for this. If you rely on night ventilation, your curtain choice and hanging method matters.
Portable AC problem 1: exhaust hose is non-negotiable and limits placement
A portable air conditioner works by moving heat from the room air into a refrigerant circuit, then exhausting that heat outside via a 150mm diameter hose. Without a window to vent to, it cannot function — it would simply move heat from one side of the room to the other. The exhaust hose is typically 1.5m long, which means the unit must sit within 1.5m of an accessible window. A 3m replacement hose (around £14.95) extends this. Rooms with windows that open inward only, skylights, or windows facing communal corridors create real installation challenges.
Portable AC problem 2: noise is the single most common reason for returns
The compressor that makes a portable AC work also makes it loud. Budget units run at 62–64 dB — roughly the volume of a loud conversation. Premium units such as the MeacoCool MC Series Pro reach 56 dB on low, which is closer to ambient office noise. Neither is silent. In a 12m² bedroom, the unit will be 2–3m from the bed; at that distance, 56 dB is audible but liveable for most people. At 63 dB, sleep disruption is a common complaint in verified Amazon reviews. This is the correct criterion to prioritise when comparing units — not BTU, which is standardised, but noise, which varies significantly between manufacturers.
Who should NOT buy blackout curtains as a primary cooling strategy
Anyone expecting room temperature to drop below outdoor temperature. Curtains reduce heat input — they do not remove heat. If outdoor temperature is 30°C and your room has already absorbed three days of heat, curtains cannot bring it below 30°C; physics prevents it. They are also the wrong solution for anyone whose primary complaint is overnight heat rather than daytime glare — by midnight, solar gain has long since ended, and the curtains' thermal benefit is zero.
Who should NOT buy a portable AC
Anyone in a room with no accessible window — or a window that cannot accommodate a 150mm hose exit. Also: anyone who is an exceptionally light sleeper and for whom 56 dB is a hard ceiling for background noise. Portable ACs are also a poor fit for rooms larger than their rated coverage: a 7,000 BTU unit in a 25m² open-plan space will run continuously without reaching setpoint temperature, driving up running costs without delivering the intended result. Buy for your actual room size, not your aspirational room size.
Versus & Comparisons — Head to Head
The comparison below measures both solutions against identical conditions: a south-facing UK bedroom, 15m², on a 32°C peak summer day. Blackout curtain specs are category averages (no verified ASIN — we carry no specific product link for curtains as this is an AC tracking site). Portable AC specs are from the two verified units in our database.
| Spec | Blackout curtains | Pro Breeze 7,000 BTU | MeacoCool Pro 9,000 BTU |
|---|---|---|---|
| Mechanism | Blocks solar radiation | Refrigerant compressor | Refrigerant compressor |
| Price | £25–80 | £240 | £449 |
| Power draw | 0 W | ~750 W | ~930 W |
| Peak temperature drop (32°C day) | 2–4°C | 8–12°C | 8–12°C |
| Can cool below outdoor temperature? | No | Yes | Yes |
| Room coverage | Any (passive) | 14 m² | 20 m² |
| Noise | 0 dB | 58 dB | 56 dB |
| Works when it's cloudy? | Minimal benefit | Yes | Yes |
| Works overnight? | No (sun not shining) | Yes | Yes |
| Running cost / hour | 0p | ~18p | ~22p |
| Installation time | 30–60 min (pole) | 20–30 min (hose) | 20–30 min (hose) |
| Works with building heat mass? | No | Yes | Yes |
| Winter heating mode? | Insulation benefit only | No | Yes (heat pump) |
Temperature drops at UK conditions (70% RH, 32°C ambient). AC specs from manufacturer data; running costs at 24p/kWh. Blackout curtain temperature benefit is real-world estimate for south-facing window, direct sun, curtains closed from morning.
The number that matters:
On a 32°C summer night when outdoor temperature stays above 22°C, blackout curtains provide zero active cooling — the sun set hours ago. A 9,000 BTU portable AC in the same room will bring 32°C down to 21°C in 25–35 minutes and hold it there. These are not equivalent tools. Curtains are a daytime passive measure; air conditioning is an active thermal extraction system that works around the clock.
Who Each Product Is For
MeacoCool MC Series Pro 9,000 BTU
Best for Bedrooms to 20m² — Heatwave ProofThe correct tool for anyone whose bedroom regularly exceeds 28°C in summer and who needs to actually sleep. The MeacoCool Pro is the quietest single-hose portable AC we track at 56 dB on low — the difference between this and a 63 dB budget unit is meaningful in a silent bedroom at 2am. It reaches the 21°C setpoint in a 20m² room faster than comparable units because the compressor is properly rated for the claimed coverage area. The heat pump means it also heats in winter at roughly three times the efficiency of a direct electric heater, spreading the £449 cost across year-round use. British-designed, with a window kit that fits UK casement and sliding windows without modification. Pair it with blackout curtains drawn during the day and the room will be at setpoint within 20 minutes of switching on.
Avoid if: The 56 dB noise on low is the most common reason for returns. If you cannot tolerate any background noise while sleeping, this — and every portable AC — is the wrong solution. Also avoid if your room cannot accommodate a 150mm exhaust hose exit through a window. The £449 price is also the honest reason many people choose the Pro Breeze instead; both cool effectively, the price difference buys lower noise and the heat pump.
Check stock →Pro Breeze 7,000 BTU Portable AC
Best Value — Rooms to 14m²The right choice for a box room, nursery, or small home office where the budget is the constraint. At £240, the Pro Breeze is the cheapest route into real refrigerant cooling rather than passive measures that fall short during a heatwave. The 7,000 BTU rating is genuinely adequate for a 14m² room — you do not need more BTU for a small space, and the lower capacity means lower running costs (roughly 18p/hour versus 22p for 9,000 BTU). Compact enough to store in a wardrobe between summers. If you have blackout curtains already reducing daytime solar gain, the Pro Breeze handles the residual overnight heat effectively in rooms up to 14m².
Avoid if: Do not use this in rooms larger than 14m² — in a 20m² open-plan room it will run continuously and still not reach setpoint during peak heat. The 58 dB noise is marginally louder than the MeacoCool; in a small room where the unit sits 1.5m from the bed, that difference is perceptible. No heat pump, so it is a summer-only purchase — the MeacoCool Pro is the better long-term investment if you plan to use it beyond June–September.
Check stock →Blackout curtains (generic category)
Daytime Passive Measure OnlyBlackout curtains are genuinely useful in UK homes, but for a different problem than active cooling. They are the right first purchase for: a room with a south or west-facing window where afternoon glare makes the space uncomfortably bright or warm during the day; a nursery or shift-worker bedroom where darkness at any hour is the primary requirement; and as a complement to a portable AC — drawn during the day so the AC starts from a lower temperature in the evening. For mild summers (peak temperatures under 28°C) in a well-insulated home, blackout curtains plus night ventilation can be sufficient without any mechanical cooling.
Avoid as a primary strategy if: your bedroom is above 30°C at bedtime, you are in your third consecutive heatwave day, or your room faces north (minimal solar gain benefit). We carry no verified ASIN for curtains — this is an AC tracking site, and for curtains you should compare pile weight, lining type, and pole compatibility at your preferred retailer.
Best in Class: Verdict
The honest answer is: use both, but understand what each does. Blackout curtains are a free-running passive measure that costs under £80and reduces daytime solar heat gain by 25–40%. They are the first thing to fit — cheap, silent, zero running cost, and they make the AC's job easier by reducing the thermal load it must handle each evening.
For active cooling: buy the Pro Breeze 7,000 BTU at £240 for rooms under 14m², or the MeacoCool MC Series Pro 9,000 BTU at £449 for rooms up to 20m². Refrigerant cooling is the only mechanism that removes heat already in the room — curtains cannot do this, fans cannot do this, and open windows cannot do this when outdoor temperature is above indoor temperature.
The combination: keep the curtains drawn on south and west-facing windows from morning. Switch the AC on an hour before bed — or use a smart plug to schedule it. The room that spent the afternoon shaded by blackout curtains will reach 21°C in 18–22 minutes. The same room with no curtains and a full day of solar gain will take 30–40 minutes. Over a 90-night summer, that is roughly 18–27 fewer AC operating hours — a saving of £3–6 in electricity. The curtains are not about the money; they are about the room being bearable when you walk in at 10pm.
The principle:
Blackout curtains keep heat out. An air conditioner takes heat out. You need the second one when the first one is no longer enough — which in a UK heatwave is usually by day two. The right question is not “which should I buy?” but “at what temperature do I need to stop relying on passive measures?” For most people, 28°C at bedtime is that threshold.
Accessories for Your Portable AC
Three accessories that materially improve the experience — none included in the box.
Window Seal Kit — £14.99
A 400cm foam seal fills the gap between the exhaust hose and the window frame. Without it, warm outdoor air re-enters the room alongside the hose, forcing the compressor to work against itself. Most units include a basic plastic bracket — the seal is the part they leave out. If your room is not cooling as expected, this is the first thing to check. View on Amazon →
Smart Plug (Tapo) — £15.97
Schedule the AC to start 45–60 minutes before bed. A room pre-cooled while you are still downstairs reaches setpoint before you need to sleep, rather than running noisily for 30 minutes while you are trying to drop off. The power monitoring feature shows real-world consumption — useful for verifying the actual running cost against the manufacturer's figures. View on Amazon →
Extension Lead (3m, BESTEK) — £17.99
A portable AC draws 700–1,000W continuously. Plug it into a quality extension lead rated for that load — not a cheap £5 strip. The BESTEK 3m lead is rated for high-draw appliances and gives placement flexibility when the nearest socket is not adjacent to the window. Do not use a cable reel extension with an AC; the cable must be fully uncoiled to avoid overheating at load. View on Amazon →
Frequently Asked Questions
Do blackout curtains actually keep a room cooler?
Yes — but only by reducing how much heat enters the room through the window. A blackout curtain blocks 80–99% of direct sunlight, cutting solar heat gain by around 25–40% compared to thin or no curtains. On a south-facing bedroom with a 1.5m² window, that can eliminate 100–180W of continuous heat input during peak sun. What curtains cannot do is remove heat already in the room — from occupants, electronics, or heat stored in walls overnight. On a 32°C day, a room that has been absorbing heat all day will still be 29–30°C even with curtains drawn, because the thermal mass of the building retains it.
How much heat does a single window let into a room?
A south or west-facing single-glazed window can admit 500–800W of solar radiation per m² at peak irradiance (roughly 11am–3pm in summer). A 1.5m² single-glazed window in a UK south-facing bedroom can therefore add 750–1,200W of heat to a room during the hottest part of the day — equivalent to running a one-bar electric heater continuously. Double glazing reduces that by 20–30%. A blackout curtain reduces it by a further 25–40% by reflecting radiation before it enters the glass. That said, the window frame, the walls, and the roof are all absorbing heat and radiating it inward too — the window is significant but not the only source.
What temperature drop can I expect from blackout curtains alone?
In a well-insulated UK bedroom on a sunny 30°C day, keeping blackout curtains closed during daylight hours typically results in a 2–4°C lower peak room temperature compared to the same room with no curtains. The effect is largest in rooms with south or west-facing windows and smallest in north-facing rooms where direct solar gain is already minimal. Once the sun sets, the benefit largely disappears — overnight temperatures depend on how much heat the building has stored during the day, which the curtains partially reduced but did not eliminate. A thermometer placed 1m from the window before and after fitting blackout curtains is the honest way to measure your specific room.
Should I use blackout curtains and an air conditioner together?
Yes — this is the correct approach and the two work on entirely different mechanisms. Blackout curtains reduce the rate at which solar heat enters the room; the air conditioner removes heat that is already present. Running an AC with curtains drawn reduces the thermal load the compressor must overcome, which means the room reaches setpoint temperature faster and the unit cycles less frequently, using less electricity. The practical saving depends on your window orientation and room size, but in a south-facing bedroom, closing the curtains before the AC starts can reduce the time to reach 21°C from 30 minutes to under 20 minutes — a meaningful difference in running cost over a summer.
Are blackout curtains worth buying if I already have a portable AC?
Yes, for two reasons. First, they reduce the cooling load the AC must handle, which shortens run cycles and cuts electricity use. Second, they keep the room cooler when the AC is off — during the day while you are out, for instance — so the room is starting from a lower temperature when you switch the unit on. A good pair of blackout curtains for a UK bedroom window costs £30–80. At 22p per AC operating hour, if they save 30 minutes of AC runtime per evening over a 90-night summer, that is a saving of roughly £10 in electricity — the curtains pay for themselves in two to three summers. The primary value, though, is sleep quality: a blacked-out room at 21°C beats a lit room at 21°C for most people.
Can I cool a bedroom with blackout curtains alone — without any AC?
In a mild UK summer (peak temperatures of 24–27°C), blackout curtains plus ventilating the room at night — opening windows once outdoor temperature drops below indoor temperature, usually after 10pm — can keep a bedroom acceptably cool without any mechanical cooling. During a heatwave where overnight temperatures stay above 20°C and daytime highs reach 30–35°C, curtains alone are insufficient. The building's thermal mass stores heat from multiple consecutive hot days faster than overnight ventilation can remove it. At that point, only a refrigerant-based air conditioner can physically extract enough heat to produce a genuinely cool sleeping environment.