Ventilation Systems · Overview
Mechanical ventilation with heat recovery
When a building is sealed tightly enough that manual airing struggles to keep up, a mechanical system can take over the job continuously — and, with heat recovery, do it without throwing away the warmth in the outgoing air.
Balanced mechanical ventilation runs two air streams at once: it draws stale, humid air out of kitchens and bathrooms, and supplies fresh air to living rooms and bedrooms. Because supply and extract are matched, the building neither pressurises nor depressurises noticeably. In newer and renovated German homes built to tight airtightness standards, a system like this is often what makes a sealed envelope livable.
What heat recovery adds
The outgoing winter air is warm; the incoming air is cold. A heat-recovery unit passes both through a core where the two streams run close together but never mix. The outgoing air warms the incoming air before it leaves, so fresh air arrives already tempered rather than icy. The household keeps the ventilation it needs while recovering much of the heat that simple window airing would lose.
Centralised systems
A single unit, usually in a utility room or loft, connects to ducts running to each room. Common in new builds and deeper renovations where ducting can be planned in.
Decentralised units
Small through-wall units serve a single room or pair of rooms, alternating supply and extract. Easier to retrofit into an existing flat without running ductwork.
Where it fits
- Tight new builds where the airtight envelope means natural air exchange is minimal by design.
- Deep energy renovations that seal an older building and need a planned replacement for the leakiness they removed.
- Homes occupied irregularly, where nobody is present to air rooms by hand during the day.
Filters and upkeep
The trade-off for "set and forget" comfort is maintenance. Filters need periodic changing and the unit occasional servicing; a neglected system moves less air and works harder. This is the routine cost that replaces the daily habit of opening windows.
Living with a system
A well-commissioned unit is quiet and largely invisible day to day. Occupants can still open windows whenever they like — the system simply removes the obligation to do so on schedule. Many homes with mechanical ventilation also keep simpler controls in reach, such as a wall thermostat for the heating, so temperature and air handling stay separate concerns.
Not a universal answer
Mechanical ventilation suits airtight buildings; in a draughty older flat with good window-airing habits it may be unnecessary. Whether a system is worthwhile depends on the building's airtightness, layout, and how it is used — questions best settled with a qualified planner rather than a rule of thumb.
Choosing a path
For most readers the sequence is: get the airing routine right first, measure humidity to understand the home's behaviour, and only then weigh a mechanical system if the building's tightness genuinely outpaces what hand-airing can manage. The two companion notes here cover those earlier steps.
References
- Heat recovery ventilation — Wikipedia.
- Ventilation (architecture) — Wikipedia, on balanced systems.
- Passive house — Wikipedia, on airtight building standards.