Why cooling an older apartment can be challenging — and what residents can do about it

Summer heat brings light and warmth, but apartment buildings can turn uncomfortably hot. In buildings constructed before the 2000s in particular, heat accumulates in the structures for days at a time — even after outdoor temperatures have dropped. Research shows that elevated indoor temperatures reduce sleep quality and slow the body's recovery. Managing indoor heat effectively has a direct impact on comfort and daily wellbeing. Bringing the bedroom temperature down enough allows for deeper sleep and noticeably better alertness the next day.

Cooling an apartment requires planning and the right approach. The structural characteristics of older residential buildings contribute to heat build-up, but indoor temperatures can be lowered through simple, cost-free measures — no expensive equipment needed.

Structural challenges in older apartment buildings during hot weather

The overheating of older apartment buildings is closely tied to the construction methods and materials used at the time. According to the Technical Research Centre of Finland (VTT), massive concrete structures absorb significant amounts of thermal energy. The thermal mass of the building stores solar radiation during the day and slowly releases it back into the indoor air well into the night. A brief evening airing is therefore often ineffective, as warm wall surfaces continue to heat the room for hours.

The ventilation system also plays a major role. Buildings constructed before the 1990s typically rely on either natural stack ventilation or mechanical exhaust ventilation without any supply air cooling. Mechanical exhaust systems draw used air out through extraction ducts, meaning replacement air flows in directly from outside — which during a heatwave means extremely warm air. Since the incoming air cannot be mechanically cooled or routed past a heat exchanger, the apartment inevitably heats up as outdoor temperatures rise.

The thermal insulation of older windows also differs considerably from modern low-emissivity glazing. Older glass allows direct solar radiation to pass through almost unimpeded, causing floors, furniture and other surfaces to heat up and radiate warmth back into the room. In newer buildings, window glazing and ventilation are designed with energy efficiency and effective summer heat management in mind.

Passive cooling: Keeping heat out in the first place

One of the most effective ways to manage indoor temperature is to prevent heat build-up before it starts. Blocking direct sunlight before it reaches interior surfaces saves considerable effort. Passive cooling is completely free, silent and uses no electricity.

In an apartment building, the most effective shading is typically achieved with interior blinds and curtains, since residents generally have no control over external structures. Venetian blinds should be kept closed and angled to reflect light back outwards. Light-coloured, dense curtains reflect heat effectively, while dark textiles absorb light and convert it into thermal energy.

Well-timed ventilation is the other cornerstone of passive cooling. Open windows only when the outside air is cooler than the air indoors — typically late in the evening, overnight or in the early morning. The most effective technique is cross-ventilation: opening windows on opposite sides of the apartment creates airflow that circulates and refreshes the air quickly. During the day, keep windows and balcony doors firmly shut to prevent hot air from entering.

It is also worth identifying internal heat sources in the apartment. Household appliances such as ovens, dishwashers and even electronics left on standby continuously generate waste heat. Avoiding oven use during hot spells and switching off unnecessary devices are easy ways to reduce the internal heat load. You can also explore other comfort-enhancing solutions and our range of resident benefits on our website.

Active cooling: Fans and portable units

If passive methods are not enough to keep temperatures under control, active cooling devices can be brought in. The most common and affordable option is a standard desk or floor fan. A fan does not actually cool the air — it simply moves it. However, the airflow it creates accelerates moisture evaporation from the skin, making the air feel around two degrees cooler than it actually is. For best results, position the fan to blow cool air upward from floor level, or place it in front of an open window in the evening to draw fresh outdoor air deep into the apartment.

More effective cooling can be achieved with a portable air conditioning unit. These devices extract heat from the air and expel it outside through an exhaust hose. The hot exhaust air must be ducted out through, for example, a sealing kit fitted to a vent window. Without a proper seal, the unit will draw in fresh hot replacement air from outside or from adjacent rooms, significantly reducing its cooling efficiency. Portable air conditioners also remove moisture from the indoor air, making it feel fresher and easier to breathe immediately.

What are residents allowed to do? Rules and responsibilities

Apartment living comes with certain restrictions when it comes to cooling. Portable devices such as fans and freestanding air conditioners may be used in all apartment types without separate notification. Fixed installations, however — such as air-to-air heat pumps — always require written permission from the property owner or housing company. A fixed heat pump requires penetrations through the external wall for the outdoor unit, which directly affects structures that fall under the building's responsibility and always requires professional installation and a careful permit process.

Modifications are particularly tightly regulated in rental and right-of-occupancy apartments. Because fixed installations affect the building's facade and electrical systems, residents are not permitted to install a fixed heat pump independently. Any costs associated with a heat pump installation are always the tenant's responsibility.

Lightweight, portable solutions are the easiest and most cost-effective way for residents to improve their comfort without lengthy permit processes or the hassle of having to remove equipment when moving out.