Byty v Praze

Local heat recovery for an apartment in Prague

Instead of a central system with ductwork, decentralised recuperation units are usually installed in flats. This is a solution tailored to Prague apartments: both panel and brick buildings, where running ducts across the layout would involve knocking down partition walls and interfering with ceilings, which makes no sense in a flat with tenants above or below.

What is a decentralised unit

A decentralised unit is a compact device installed directly into the external wall or window frame of a single room. It draws in outside air, transfers heat from the outgoing indoor air via a small heat exchanger, and supplies it back inside filtered. Each unit serves one room, so several units are typically combined in an apartment depending on which rooms you wish to cover.

Flats in Prague: prefabricated concrete, brick, attic extension

In panel buildings, the main topic is the external wall, on standardised panels, a suitable location for the penetration can be found that does not conflict with reinforcement or services. In brick buildings with thicker walls, drilling is technically more demanding, but space is usually not an issue. For attic conversions, where the façade is often insulated and the wall construction differs from the rest of the building, the location needs to be discussed individually. This is precisely what is addressed during the survey.

SVJ consent and façade penetration

Since the unit passes through the external wall, it technically constitutes an intervention in the common parts of the building. In an owner-occupied flat this requires consent from the building's owners' association; in a rented flat, consent from the landlord. Obtaining this consent is usually a formality for a single small opening, but it must be factored into the schedule, installation "on the spot" is not possible.

Hluk

Decentralised units have several speed settings. On the lower setting, which is sufficient for standard all-day ventilation, operation is quiet enough to go unnoticed in the room during the day. The unit is louder at maximum output. This is used more intermittently rather than continuously. We select the capacity and location so that the unit runs long-term on a lower setting.

Location

Most commonly, the indoor unit is installed in the wall under or near the window; in bedrooms, typically opposite the bed or on a side wall to prevent airflow from blowing directly onto sleeping occupants. In living rooms, the main considerations are electrical access and ensuring the outdoor grille does not conflict with neighbours' window sills or balconies.

When one or two units suffice and when more are needed

If you are primarily addressing the bedroom, where stale air is most noticeable in the morning, one unit is often sufficient. Two units typically cover the bedroom and living room: the most frequently used rooms in an apartment. For larger apartments with multiple rooms where you want controlled ventilation throughout, the number of units is calculated based on the number of habitable rooms; bathrooms and kitchens usually have their own extraction and are not included in this count.

Facade penetration step by step

The opening for the unit is small, measuring just a few centimetres in diameter, but it passes through the entire external wall assembly, so core drilling is required. For panel buildings, reinforcement bars and any services within the panels are checked beforehand to ensure drilling does not compromise structural elements. On insulated facades, additional attention is given to connecting and sealing the external grille into the insulation layer to prevent thermal bridging or moisture ingress at the penetration point.

Operation and consumption

The decentralised unit runs practically non-stop at low capacity, occasionally switching to a higher mode: typically when cooking, showering in an adjacent room, or when there are more people in the room. The electricity consumption of one unit is low, comparable to a small household appliance, because the motor operates with a small air volume for a single room.