The Spring 2027 Reset: Switching Your Home Back from Heating to Cooling

This is the companion to our autumn changeover guide — the same weekend’s work, in the opposite direction. Between them they bookend the year.

Why March, not May

Two reasons, and both are about being early.

UK heat is arriving earlier. A heatwave ran 24–27 May 2026, associated with an estimated 753 heat-associated deaths in England, with 31.5°C recorded at Kew Gardens on 26 May. May is now inside the season, not before it.

Buying in a heatwave is the worst possible timing. During the June 2026 heatwave, UK retailers reported air conditioner and fan supply running low amid a buying frenzy. Anyone ordering that week faced restricted choice, firmer pricing and delivery dates arriving after the heat had passed. Our buying timing guide covers the calendar properly.

There’s also a 2027-specific argument: NOAA has El Niño at a greater than 90% chance of reaching very strong for autumn and winter 2026–27, and global temperature typically peaks in the year after an El Niño peaks. Our Summer 2027 guide covers this — with the honest caveat that El Niño’s direct UK signal is weak, so treat it as a reason to be organised rather than a forecast.

1. Bring the air conditioner back into service

If you stored it properly in autumn, this is quick. If you didn’t, this is when you find out.

1. Stand it upright for a few hours before switching on, especially if it’s been moved or tilted — refrigerant and compressor oil need to settle correctly.
2. Check and clean the filter. Rinse under lukewarm water and let it dry completely before refitting. Our maintenance guide covers the full routine.
3. Inspect the hose for creases or splits from being stored folded.
4. Run it for twenty minutes on a mild day. Confirm it powers up, the compressor engages, and cold air actually comes out.
5. Check for smells. A musty smell means moisture got in over winter — our smell guide covers fixing it, and it’s much easier now than in July.

If it doesn’t work, our won’t turn on and not cooling properly guides cover the common causes. Discovering this in March means you have options.

2. Fit and check the window kit

The single biggest determinant of how well a portable unit performs, and the thing most likely to go wrong.

Fit it now, properly, and check the seal is genuinely airtight. Any gap lets hot air straight back in — and with a single-hose unit, the negative pressure it creates actively pulls outside air through every gap in the room. Our hose configuration guide covers why this matters more than people think, and our seal kits guide covers getting the fit right.

If your window shape is awkward — a sash, a roof window, a bifold — sort it now. Our sash window guide covers fabricating a board if no standard kit fits.

3. Get the shading sorted — the highest-value job

Worth more than any appliance, because stopping heat entering beats removing it afterwards.

• External shading beats internal, decisively. Awnings, external blinds, shutters — anything that intercepts sunlight before it reaches the glass. Our shading guide covers options, and spring is when installers have availability.
• Reflective window film on the worst sun-facing windows — cheap, effective, and best applied before the season. Our film guide covers what works.
• Thermal or blackout curtains where external options aren’t practical.
• Work out which windows get direct sun and when. Walk the house at 10am, 2pm and 5pm on a clear day and note it. That tells you which rooms need shading closed and from what time.

4. Reverse the curtain and window routine

The opposite of winter, and it takes a conscious switch.

Winter: curtains open during the day for solar gain, closed at dusk to retain heat.

Summer: curtains and blinds closed on sun-facing windows during the day — crucially, closed before the room heats up, from mid-morning, not after it’s already warm. Open in the evening.

Same for windows: open only when it’s genuinely cooler outside than in, which in a UK summer usually means overnight and early morning. Our window timing guide covers the discipline — with the important caveat that on a tropical night there’s no cooler air to bring in, covered in our tropical nights guide.

5. If you have a heat pump unit, just switch modes

One of the genuine advantages of reverse-cycle units: there’s no changeover. It’s been heating all winter; now it cools. Nothing to store, nothing to set up, no window kit to refit — that stayed in place through winter, because heating mode also needs it.

Still clean the filter. Our heating mode guide covers how these work.

6. Buy anything you’re missing

March and April give you full stock, normal pricing and next-day delivery. Work out capacity properly using our BTU calculator guide before shopping, because the most expensive mistake is buying an undersized unit because it’s the one in stock.

Buy the accessories at the same time — window seal kit, spare filter, extension hose. These sell out faster than units during a demand spike, because they’re cheap impulse purchases.

7. Wind the heating down properly

• Don’t switch the whole system off in March. Cold snaps happen well into April, and completely unheated rooms develop damp — our condensation guide covers why. Turn the thermostat down and shorten the schedule rather than switching off entirely.
• Turn TRVs down, not off, in rooms you’re no longer heating.
• Run the system briefly once a month over summer to stop pumps and valves seizing.
• Book the boiler service now if you didn’t in autumn — spring availability is far better than October’s.

8. The people bit

• Register for Heat-Health Alerts from UKHSA and the Met Office if you haven’t. Free and region-specific. Our alerts guide explains the colour levels.
• Check on anyone vulnerable and make sure their cooling is set up and tested — our elderly heatwave guide covers this.
• If anyone has hay fever, our hay fever prep guide covers the pollen-versus-ventilation conflict, which peaks in June.

The weekend plan

Frequently asked questions

Sources

• UKHSA / GOV.UK — Heat mortality monitoring report, England (May 2026 heatwave mortality estimate)
• NOAA Climate Prediction Center — ENSO Diagnostic Discussion (>90% very strong El Niño, winter 2026–27)
• Met Office — Heat-Health Alerts
• Met Office — Pollen forecast
• Energy Saving Trust — Thermostats and heating controls

Related reading: our autumn changeover guide and Summer 2027 preparation guide.