When temperatures climb in July, your home quickly turns into a heat trap: rooms and especially attic spaces heat up to over 30 degrees Celsius (Verbraucherzentrale), it barely cools down at night, and restful sleep becomes hard to find. Yet hot summers are no longer the exception. In Germany, the number of hot days above 30 degrees has more than tripled since 1951, from around three to about ten days per year (Umweltbundesamt), and the summer of 2024 brought a nationwide average of 12 hot days (Deutscher Wetterdienst), almost three times as many as usual. The good news: with smart technology, your home can largely keep itself cool, through shutters controlled by schedule and sun position, through a fan and air conditioner that run by schedule and temperature sensor, and through an app that lets you keep an eye on everything while you are out. This guide explains what passive shading achieves, when active cooling is worthwhile, what the electricity costs and what can be done in a rented flat, and how we set up the whole cooling automation during a home visit.
Key takeaways
- Hot days are increasing: the number of days above 30 degrees has more than tripled since 1951, and the summer of 2024 brought an average of twelve hot days.
- The most important lever is passive: external shading that keeps solar heat from entering through the window at all, because ordinary window glass lets 60 to 70 percent of solar energy through.
- Smart shutters and blinds lower themselves by schedule or sun position, entirely without daily readjustment and even when no one is home.
- A fan and an air conditioner can be controlled by schedule and temperature sensor and switched on and off from anywhere via app.
- A fan is very economical, an air conditioner uses considerably more electricity, which is why shading and smart control should reduce the cooling demand first.
- Much of this also works in a rented flat without structural changes, and we set up the right combination during a home visit and explain it patiently.
Why Summers Keep Getting Hotter
The fact that homes heat up more in summer than they used to is not a subjective impression but well documented. A hot day is defined as a day on which the maximum temperature rises above 30 degrees Celsius. Their number in Germany has more than tripled since 1951, from around three to about ten days per year (Umweltbundesamt). In the multi-year average from 1961 to 1990 there were still 4.2 hot days (Umweltbundesamt) per year. Notably, the ten years with the most hot days have all been recorded since 1994 (Umweltbundesamt). In particularly hot years such as 2003, 2015 and 2018, the nationwide average even reached 18 to 20 hot days (Umweltbundesamt).
The summer of 2024 fits this picture. The German Weather Service counted an average of around 52 summer days (Deutscher Wetterdienst) above 25 degrees and 12 hot days (Deutscher Wetterdienst) above 30 degrees, almost twice as many summer days and almost three times as many hot days as in the long-term average. The average summer temperature was 18.5 degrees Celsius (Deutscher Wetterdienst), 2.2 degrees above the reference period 1961 to 1990. The first hot day fell as early as 6 April (Deutscher Wetterdienst), earlier than ever since records began, and the highest temperature was measured at 36.5 degrees (Deutscher Wetterdienst) on 13 August in Bad Neuenahr-Ahrweiler.
It is not only the day that is a strain, but increasingly the night. A tropical night is defined as a night when the minimum temperature does not fall below 20 degrees Celsius (Deutscher Wetterdienst). If the home stays warm at night, the body lacks recovery, and the rooms barely cool down between two hot days. That is precisely why it is often not enough to fight the heat only during the day. Anyone who wants to live comfortably in the long run needs an interplay of keeping the heat out during the day and deliberately cooling down in the cooler hours, and both can be automated.
Most heat comes in through the windows
Passive Shading: Keep the Heat Outside
The most effective and at the same time cheapest protection against heat is shading that intercepts the sun's rays before they enter the room through the window. The Verbraucherzentrale stresses that sun protection should always be fitted on the outside where possible, because only external roller shutters, raffstores or awnings keep the heat away before it builds up behind the pane. An internal curtain can darken the sun, but the heat is then already in the room. Dark surfaces heat up to as much as 80 degrees Celsius (Verbraucherzentrale) in the sun, while light surfaces stay cooler thanks to better reflection.
Shading becomes smart as soon as it is no longer operated by hand but automatically. Electric shutters and blinds can be lowered by schedule or by sun position. That keeps the home protected even when you leave in the morning and the sun only reaches the south side at midday. A brightness or temperature sensor can additionally trigger the shading depending on the weather. How such sequences can be planned and linked with other devices is something we are happy to clarify beforehand in smart home advice.
By schedule
The shutters lower in good time in the morning, before the sun heats the room, and rise again in the evening, without you having to think about it.
By sun position
A brightness or weather sensor lowers the shading exactly when the sun hits the respective window side and opens the view again as soon as it moves on.
Via app while you are out
If it has unexpectedly become hot, you close the shading from anywhere, so the home is pleasantly cool when you return.
Scheduled shutters help twice over
Active Cooling: Control Fan and Air Conditioner Smartly
When passive shading is no longer enough on very hot days, active cooling comes into play. A fan does not really cool the air, but the air movement provides a noticeable cooling effect on the skin and is very economical. An air conditioner actually lowers the room temperature but uses considerably more electricity. Both devices can be controlled smartly: via a switchable socket, a schedule and a temperature sensor that starts the cooling only above a certain room temperature and switches off again as soon as it is pleasant.
The real gain in comfort is that you no longer have to think about it. The fan only runs when a room really gets too warm, the air conditioner pre-cools the bedroom an hour before bedtime, and from anywhere you switch both via app. For this to work reliably, you need a stable home network reaching every room, otherwise the devices lose their connection. How to eliminate dead spots is shown in our article on stable wifi throughout the house, and on request we set up the matching control right away with the smart air conditioner.
- The fan starts automatically as soon as the temperature sensor exceeds a set room temperature.
- The air conditioner pre-cools the bedroom by schedule in good time before the night's rest.
- A window contact can stop the cooling as soon as a window is opened, so no energy is wasted.
- From anywhere you switch the fan and air conditioner on via app, so the home is cool when you return.
- All devices can be bundled in one app, so that shading and cooling work together as a single system.
Cool when electricity is cheap
Passive or Active? An Honest Comparison
Passive shading and active cooling are not opposites but build on each other. Anyone who keeps the heat out with shading in the first place needs to cool actively less afterwards and thus saves electricity. The following overview sorts the common approaches by cooling effect, electricity consumption and purpose, so the order becomes clear: first keep the heat outside, then cool down in a targeted and economical way.
| Approach | How it cools | Electricity use | Well suited for |
|---|---|---|---|
| Smart shading (shutters, blinds) | keeps solar heat away in front of the window | very low, only the drive | the basis in practically every home |
| Fan | moves the air, noticeably cools the skin | 25 to 50 watts, around 6 to 10 euros a year (Verbraucherzentrale) | individual rooms and dry heat |
| Mobile air conditioner (monoblock) | cools actively, waste heat through a hose to the outside | high, around 35 to 140 euros a year (Verbraucherzentrale) | flexible use without structural changes |
| Fixed split air conditioner | cools quickly and efficiently per cooling output | lower per cooling output, but installation needed | those who want to cool permanently and efficiently |
The comparison shows: a fan is the most economical helper for individual rooms, a mobile air conditioner brings real relief on extreme days but costs more electricity, and a fixed split unit cools most efficiently but requires installation. Which combination is worthwhile for your home is best clarified on site. That is exactly why, during advice, we look at your rooms, the window orientation and your daily routine and honestly recommend what really helps and what is not necessary.
Keeping an Eye on Electricity and Costs
Cooling should not be a nasty surprise on the electricity bill at the end of the year. A fan is harmless here: with 25 to 50 watts (Verbraucherzentrale) and around 900 operating hours a year, it comes to electricity costs of about 6 to 10 euros (Verbraucherzentrale) per year. A mobile air conditioner costs between 300 and over 1,000 euros (Verbraucherzentrale) to buy depending on the model, and in operation the Verbraucherzentrale reckons with around 35 to 140 euros (Verbraucherzentrale) per year, depending on how often and how long you cool.
The cooling speed also differs considerably. In one test, a split unit cooled a 14-square-metre room from 30 to 24 degrees in less than 5 minutes (Verbraucherzentrale), while a mobile monoblock device needed 30 to 45 minutes (Verbraucherzentrale) for the same. The reason: with a monoblock, the whole device stands in the room, and the exhaust hose at the window gap often lets warm air flow back in. An air conditioner should therefore not run continuously but cool individual rooms in a targeted way, and that is exactly what you achieve with a schedule and temperature sensor.
An air conditioner is no substitute for shading
For the control to work smoothly in everyday life, a reliable home network is the foundation. If smart sockets or sensors react with a delay because of a weak radio signal, the comfort is lost. That is why, before setup, we check the radio coverage and fix weak spots, just as we do with wifi optimization at home. On a stable basis, shading, fan and air conditioner can then be linked into a system that works in the background.
What Is Possible in a Rented Flat
A common misconception is that smart cooling technology only works in a house you own. In fact, much of it can be done without structural changes and without the landlord's consent. Electric shutter motors are available as retrofittable belt winders that replace the existing shutter belt and can be controlled by schedule. Fans and mobile air conditioners stand freely in the room anyway, and smart plug adapters make any normal device switchable, entirely without tools. This makes a large part of the cooling automation tenant-friendly.
- Retrofittable radio belt winders replace the existing shutter belt and control the shading by schedule.
- Smart plug adapters switch the fan or air conditioner without changing anything in the wiring.
- Mobile air conditioners and fans can be set up at any time and taken along again when you move out.
- Temperature and window sensors work by radio and require no fixed installation.
- For external blinds, awnings or fixed split units, it is worth arranging things with the landlord in advance.
Living cool is not a question of ownership or renovation, but of the right combination of shading and economical cooling. Most of it can be set up in a rented flat too.
How We Set Up the Cooling Automation for You
As great as the benefit is, it easily fails in practice when shutters, sockets, sensors and apps do not work together. This is exactly where our on-site service comes in. We come to your home, look at the window orientation, the existing shading and your daily routine and set up the technology so that it works on its own on hot days, without daily readjustment. You do not have to prepare anything or wade through a manual.
1. Analyse on site
We check which rooms heat up the most, how the windows face the sun and which shading already exists, and honestly recommend what makes sense.
2. Set up shading and devices
We equip shutters or blinds with schedule or sun-position control and connect the fan and air conditioner to switchable sockets and a temperature sensor.
3. Link automation and app
We check the home network, fix dead spots and bring everything together in one app, so shading and cooling run as a single system, controllable from anywhere too.
4. Explained patiently
We brief you calmly, show the few actions needed in everyday life and remain reachable as your personal contact if a question comes up later.
We bill this support via a clear home-visit flat rate, so the costs stay plannable. We make sure operation stays simple even if you feel unsure about technology, similar to what is described for the smart home for seniors. And anyone who would like to get to know control by voice or app in a relaxed way will find easy first steps in our article on artificial intelligence in everyday life. On request, we also guide you calmly through the operation as part of our tech help for seniors. This turns individual devices into a coherent system that keeps the home cool on its own in summer.