The IDAE, Spain's national energy agency, has a piece of winter advice that costs little to follow and that almost nobody does: close your shutters and curtains at night to avoid significant heat loss, as it says in its energy-saving advice for homes (in Spanish). The problem is the timing. In early December the sun sets in Barcelona at around twenty past five, and at that time many people still aren't home: by the time they get in, the living room has been losing heat through the glass for quite a while.

The other half of the advice works the other way round: during the day, on windows that get the sun, it pays to keep the shutter up and let it in. In winter your shutters work for your heating: up when the sun is on them, down as soon as it sets. Doing it by hand every day is impossible to keep up; with shutters that already have a motor, the house does it by itself, and this guide explains how it decides when.

Why heat escapes through the window

The window is the weak point of any home in winter. According to the IDAE's practical energy guide (in Spanish), between 25% and 30% of our heating needs are due to heat lost through windows. It makes sense: glass insulates far less than a wall, and at night it's the coldest surface in the room.

A lowered shutter won't turn single glazing into a new window, but it puts a barrier in front of it, with a layer of air between the slats and the glass, so the glass is no longer directly exposed to the cold night air. That's why the IDAE's advice is about night-time: it's when the difference between inside and outside is greatest, and when the light coming in no longer matters.

There's a limit worth knowing about. The shutter rolls up into its box above the window, and if that box isn't insulated it lets cold air in whether the shutter is up or down. The same guide lists uninsulated roller-shutter boxes among the places where heat escapes, and the IDAE advises making sure they have no gaps and are properly insulated. That's a job for a carpenter, not for home automation: automating the shutter won't fix it.

During the day: up as soon as the sun is on them

In winter the sun is low. In Barcelona, at noon on 21 December it's about 25° above the horizon, compared with more than 70° in June, which is why its rays come in almost sideways and reach the back of the room. It's heat you don't pay for: the IDAE guide points out that well-oriented windows let solar radiation straight into the space that needs heating in winter, which saves on heating.

So in winter the system raises the shutters during the day. For each window it knows which way it faces, and therefore when the sun is on it: south-facing ones get it almost all day; east-facing ones, in the morning; west-facing ones, in the afternoon. It also takes the street into account. On a narrow street, the building opposite blocks the low winter sun long before it sets, so each window is told the height of the sun below which it no longer gets any.

Windows that never see the sun — north-facing ones, or those onto a courtyard — also stay up during the day, but for the light, not the heat. And there's a cap on too much of a good thing: if a sunny room gets too warm, the shutter lowers to a shade position. By default that cap is 24 °C, and if the system also controls the heating, its setpoint plus 2 °C. A south-facing living room can get there on a clear January lunchtime, and there's no point being too hot in the middle of winter.

At dusk: down, even if you're out

When the sun sets in winter, the shutters come down. Not at a fixed time, which would need changing every few weeks and again when the clocks change, but with each day's sunset, which the system works out for your home. In December that's around twenty past five in the afternoon, and the house starts holding on to its heat from that moment, whether anyone is in or not.

In the morning the order is reversed: the shutter goes up once the sun is above the horizon, and never before the time you set for each room. In the living room it can be early; in a bedroom, at the time you get up, so the sun doesn't wake anyone.

Closing at night can be switched off window by window in the app. If you'd rather see the street at night from one room, that shutter stays where it is and the others keep coming down.

When winter starts for your home (it's not the calendar)

In summer, the same shutter does the opposite: it comes down to give shade on whichever side is in the sun. The question is when winter begins, and in Barcelona the calendar doesn't decide it: there are T-shirt Novembers and coat-wearing Marches. The system decides using the average outdoor temperature over the last seven days. Below 14 °C it switches to winter, and it doesn't go back to the in-between mode for autumn and spring until the average rises above 16 °C. That margin stops it changing mode every time a couple of mild days come along.

And if the heating is in charge, the shutter follows. When the system also controls the heating and it's in heating mode, the shutter behaves as it would in winter, whatever the average says. It doesn't matter whether that's the split unit in the living room or the boiler: we explain how to schedule each one separately, in our guide to split units and radiators in a flat without gas and in the one on the smart thermostat for your boiler.

What it respects: your hand, the terrace and the rain

A shutter that moves by itself is only convenient if it doesn't fight you. So the system steps aside in these cases:

  • Your hand comes first. If you raise or lower a shutter with the usual switch or from your phone, the automation leaves it alone for a few hours: three by default, and you can change that in the app.
  • The terrace door. If the balcony or terrace door has an opening sensor, the shutter won't come down while it's open, and it waits a few minutes after you close it. Nobody gets shut out.
  • The rain. With a rain sensor, you choose what each shutter does when it rains: treat it as a day without sun, go to a set position or stay put.
  • What matters most. More natural light, a balance, or more savings: you choose in the app, for the whole house or for one particular shutter. With ‘savings’, in winter the shutter always comes down at dusk, even if you've switched off closing at night for that window.

All of this is decided locally, on the small device that runs the house, so the shutters keep to their programme even if the internet goes down.

What you need (and what it costs)

The starting point is shutters that already have a motor and go up and down with a wall switch or a remote. If yours are still operated by a crank or a strap, a shutter specialist needs to motorise them first; we don't install motors, but in our guide on how to automate the blinds in your home we explain which motor to ask for so it integrates without problems later.

With that in place, the installation is a module behind each switch (over Zigbee or Z-Wave, with no building work, and the switch keeps working as before), a temperature sensor in the sunniest rooms, and the outdoor temperature, which comes from a sensor in the shade or from the weather forecast. It all goes into the same smart blinds system that looks after them the rest of the year.

Automating 2–3 blinds that are already motorised, with app and voice control, starts from €400; the number of shutters and how they're operated today are what move the price, and we look at that during the visit, with no obligation. It comes with the same warranty as everything else we install: we guarantee our installation and configuration for 5 years. The devices carry their manufacturer's warranty (2–3 years), and we handle it for you.

Common questions

Does lowering the shutters at night really make a difference?

It does, although how much depends on your window. The IDAE, Spain's energy agency, estimates that between 25% and 30% of a home's heating needs come from heat lost through the windows, and it recommends closing shutters and curtains at night to avoid significant heat loss. With single glazing and an old aluminium frame the difference is bigger than with good double glazing. What we won't promise you is a savings percentage; what does change for certain is that the shutter comes down at the right time every day, not whenever someone remembers.

My flat faces north or onto an inner courtyard. Is it worth it?

Partly. A window that gets no direct sun in winter doesn't receive any free heat, so during the day the shutter stays up just for the light. But closing at dusk works just the same: heat escapes through the glass whichever way it faces, and lowering the shutter as soon as the sun sets is exactly what the IDAE recommends.

Could I get shut out on the terrace with the shutter down?

No. If the balcony or terrace door has an opening sensor — and on doors that lead outside it's worth fitting one — the shutter won't come down while the door is open, and it waits a few minutes after you close it before moving.

My shutters are operated by a crank or a strap. Can they be automated?

First they need a motor, and that's a job for a shutter specialist: we don't install motors or replace axles. Once they go up and down with a wall switch or a remote, we add the control and integrate them with the rest of the house. In our guide on how to automate your blinds we explain which motor to ask for so it integrates without problems later.

What if one day I want to leave it up?

Move it with the usual switch or from your phone, and the automation steps aside: for a few hours (three, by default) it won't touch that shutter again. After that, it picks up its programme again at the next movement it's due. And if there's a window you'd rather never close at night, closing at dusk can be switched off for that one alone in the app.

In short

In winter, the shutter is the part of your heating that uses next to nothing. Up during the day, so the low sun comes in through the windows that get it; down as soon as it sets, which is when the IDAE recommends closing it; with a cap so the living room doesn't overheat, and respecting your hand, the terrace door and the rain. All it needs is for someone to move it at the right time every day, and that's exactly what an automated home does better than anyone. Shutters that already have a motor can help your heating every day of the winter: they just need to know when.