Heat recovery ventilator

A heat recovery ventilator (HRV, supply-and-extract unit with heat recovery) is a ventilation device in which the warm exhaust and cold supply streams pass through a heat exchanger without mixing. Heat from the outgoing air is passed to the fresh air, so in winter the air entering the apartment is already partly warmed rather than icy from outside.

How it works. Inside are two fans (supply and extract), a heat exchanger and filters. The main exchanger types are plate (streams pass through thin plates), rotary (a rotating drum carries heat and sometimes moisture), and reversing or cyclic units, which switch flow direction about every 30-60 seconds while heat is stored in a ceramic or other accumulator. Several such units in one apartment must be synchronised in antiphase.

Efficiency. The efficiency of plate heat exchangers, according to different sources, is roughly 40-92%, and some manufacturers claim up to 93% for individual models. Reviews more often speak of recovering up to 80% of the heat. Real efficiency depends on the model, airflow and temperature difference, so check the datasheet and test conditions. A heat recovery ventilator saves energy on heating the air but does not replace heating.

Formats. Supply-and-extract units can be room units (in the wall of one room, without ducts), central ducted units for an apartment or house with a duct network, and ceiling-mounted models. A ducted system is quieter and can supply bedrooms and the living room, but needs space for the unit and ducts above the ceiling. Room units are easier to install but have to be placed in several rooms.

Noise and maintenance. Noise depends on mode and model: some models give around 16-30 dB in normal mode, but each unit has its own datasheet. Filters must be cleaned or replaced regularly, and the exchanger checked according to the manufacturer's instructions. Choose a model with accessible servicing and space for an access hatch.

When to choose it. A heat recovery ventilator is especially useful in a cold climate, where airing through windows in winter chills the apartment and heating outside air directly with an electric heater is expensive. Pros: filtered clean air, less street noise. Cons: unit cost, ducts, maintenance. The air-exchange calculation is made by the designer according to codes and your lifestyle; we do not quote per-person figures without a verified norm. In country house projects we plan ventilation and duct routes at the design stage, because they are almost impossible to hide later.