How to save on air conditioning without sweltering this summer

In summer, air conditioning can be the appliance that weighs most on your bill. The good news is that the difference between using it well and using it badly is enormous: you can cool the house while spending considerably less, without giving up comfort. These are the adjustments you really notice, and the myths it's worth letting go of.

The magic temperature: 25-26 degrees

Every degree you lower the thermostat increases consumption noticeably. As an order of magnitude, the rule technicians work with is that each degree less means around 7-8% more spent.

Setting the air conditioning to 21 degrees doesn't cool the room any faster: it just makes the unit run at full power for longer and leaves you cold. At 25-26 degrees you're comfortably cool, the compressor gets a rest sooner, and the contrast with the street outside is still pleasant.

If your unit has an automatic or eco mode, use it: it adjusts the power to the room's actual temperature instead of always running flat out.

Degrees aren't the only thing: humidity counts too

A good part of that muggy feeling is humidity, not temperature. The dehumidify mode (dry) uses less than cooling mode and, on humid but not extreme days, leaves the house more comfortable with the thermostat set higher. It's one of the most underused buttons on the remote.

Make the most of thermal inertia and the cooler hours

• Air the house at night and first thing in the morning, when the outside air is cool, and close the blinds and lower the awnings during the sunniest hours. Blocking the heat before it gets in costs nothing and makes the biggest difference of all.
• Don't cool empty rooms: close doors and only cool the room you're in.
• Switch it off a little before you go out: the room keeps its coolness by inertia for a good while.
• Combine it with a ceiling fan: it uses a fraction of what air conditioning uses and helps spread the coolness around. With a fan going you can turn the thermostat up a couple of degrees without noticing the difference.

The maintenance almost nobody does

A dirty filter forces the unit to work harder to move the same air, and you pay for that every day. Cleaning the filters every few weeks in high season is the best effort-to-saving maintenance job there is: it takes five minutes and improves both performance and air quality.

Two more, once a year:

• Check the outdoor unit: that it isn't covered up, or in direct sun if that can be avoided, or with leaves and dirt blocking the grille. A unit that can't expel heat uses more.
• Check the refrigerant charge. A unit with a leak cools worse and uses more, and it often goes unnoticed for whole seasons.

The three myths that cost money

"It's better to leave it on all day than to switch it off and on again." False in most cases, and true in some. With inverter units (practically all modern ones), holding a steady temperature for several hours at a stretch is indeed more efficient than switching off and starting up again every so often, because starting up is what uses most. But leaving it on for eight hours with nobody in the house is never worth it. The useful rule: short absences, leave it; long absences, switch it off.

"Setting it to 18 cools it down faster." No. The unit cools at its maximum rate until it reaches the temperature you've set. Setting it to 18 doesn't speed anything up: it just keeps it cooling when it should already have stopped.

"Air conditioning is no use for heating." Almost all current units are heat pumps, and when heating they're markedly more efficient than an electric radiator: they produce several units of heat for every unit of electricity. If you have air conditioning, you already have efficient heating installed — it's worth bearing in mind come winter.

Time-of-use bands count too

On the 2.0TD tariff, electricity doesn't cost the same at all hours. The summer peak hours — 10:00 to 14:00 and 18:00 to 22:00 on working days — coincide exactly with the hottest ones, which is the worst possible combination.

Two moves that work:

• Cool the house early: bring the temperature down before 18:00 and let thermal inertia do the rest through the expensive band.
• Make the most of the weekend, which is off-peak 24 hours a day.

The bands, with their exact hours, are in electricity prices by time of day: peak, standard and off-peak. And if you have solar panels, running the air conditioning at midday is one of the loads that fits solar production best — we talk about that in solar panels and self-consumption.

Keep an eye on your contracted power

If switching the air conditioning on alongside the oven or the hob trips your main breaker, it isn't that the air conditioning uses "too much": it's that your contracted power falls short for that combination. And the other way round: if it never trips, you probably have power to spare and you're paying a higher fixed charge all year round. It's the most common overcharge we see, and it's fixed with a single phone call: how to lower your contracted power.

And the adjustment that saves the most: the right tariff

All these tricks reduce how much you consume. But if your tariff isn't competitive, you'll be overpaying for every kilowatt whatever you do. That's why the biggest saving is usually in the contract, not just in your habits: the cleanest filter in the world doesn't make up for a kWh price 30% above the market.

At luzgasia you upload your summer bill — the one that shows your consumption in the worst month — we analyse it and tell you whether your tariff makes good use of your profile or whether you could be paying less. And if you've already got a good one, we'll tell you that too.

It's free, with no strings attached and no sales calls. Analyse your bill now and face the summer with your bill under control.