Comfort Ventilation with Heat Recovery (Central or Semi-Decentralised)

Mechanical supply and extract ventilation with heat recovery (typically 80-92 % recovery rate) replaces uncontrolled window ventilation.

How does mechanical ventilation with heat recovery work?

Mechanical ventilation with heat recovery (MVHR), also known as comfort ventilation or controlled residential ventilation, mechanically extracts stale air from kitchens, bathrooms and WCs and supplies living and working rooms with filtered outdoor air. Its core is the counterflow plate heat exchanger: extract air and supply air pass each other in separate channels, with 80 to 92 % of the heat content of the extract air transferred to the cold fresh air. This figure is called the heat recovery efficiency or temperature ratio. The air streams do not mix. Central systems serve an entire building via a duct network; semi-decentralised units serve one dwelling each. The fan electricity consumption is 0.2 to 0.45 Wh per cubic metre of air, far less than the heat recovered.

Which buildings benefit from MVHR?

High efficiency requires an airtight building envelope. The decisive figure is the n50 value, the air change rate at a 50 Pa pressure difference in the blower door test; it should not exceed 1.5 per hour. In unrefurbished buildings with high infiltration, too much air flows uncontrolled through leaks, so the heat recovery is largely wasted. Typical properties are low-energy and passive houses, office buildings and schools. Space is also needed for the unit and duct routing, along with organised filter maintenance. In existing buildings, retrofitting usually makes sense as part of a comprehensive refurbishment, when the envelope and windows are being made airtight anyway.

What does MVHR actually deliver?

In well-insulated buildings, heating energy demand falls by 20 to 40 %. The saving is calculated from building volume, air change rate, temperature difference and heating hours, multiplied by the heat recovery efficiency, minus fan electricity. A detached house with 450 m³ of heated volume saves a net 4,200 kWh/a and roughly 0.85 t CO2. A central system in a detached house costs €12,000 to €22,000; semi-decentralised apartment ventilation units cost €5,000 to €9,000 per dwelling. With a service life of 20 years, the purely energy-based payback is 15 to 25 years. In practice, the real drivers are consistently good air quality, protection against moisture damage and mould, and pollen and noise protection.

Energy carrier

Erdgas, Heizöl, Pellet, Fernwärme, Strom → Erdgas, Heizöl, Pellet, Fernwärme, Strom

Savings potential

20-40 % Heizenergie (in gut gedämmten Gebäuden)

Worked example

A detached house with 450 m³ of heated volume and an airtight envelope has so far been ventilated via the windows and heated by a gas boiler (efficiency 0.90). A central MVHR system with a heat recovery efficiency of 0.85 is retrofitted. At an average air change rate of 0.4 per hour and a 12 K temperature difference between inside and outside, the ventilation heat loss is 450 × 0.4 × 1.2 × 0.34 × 12 = 881 W. Over 5,500 heating hours, that is 4,846 kWh without heat recovery and only 4,846 × (1 − 0.85) = 727 kWh with heat recovery. Referred to the boiler efficiency, this saves (4,846 − 727) / 0.90 = 4,577 kWh of gas. After deducting 350 kWh of fan electricity, a net final energy saving of 4,227 kWh remains, rounded to 4,200 kWh per year, and roughly 0.85 t CO2. On top of that comes noticeably better air quality.

Investment & payback

EFH zentral: 12.000-22.000 €; pro Wohnungslüftung (semi-dezentral) ca. 5.000-9.000 €/WE · Service life: 20 a · Payback: 15-25 (Komfort als Treiber) a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

How much heating energy does a ventilation system with heat recovery save?

MVHR reduces heating energy demand in well-insulated buildings by 20 to 40 %. The heat exchanger transfers 80 to 92 % of the extract air heat to the supply air. A detached house with 450 m³ of volume saves a net 4,200 kWh per year after fan electricity is deducted. In leaky older buildings the saving is considerably lower.

How much does an MVHR system cost for a detached house?

A central MVHR system costs €12,000 to €22,000 in a detached house, including duct network and installation. Semi-decentralised apartment ventilation units in multi-family buildings cost €5,000 to €9,000 per dwelling. The purely energy-based payback is 15 to 25 years over a 20-year service life, which is why air quality and moisture protection are the stronger arguments.

Do you need an airtight building envelope for a ventilation system?

Yes, an airtight envelope is a prerequisite. The n50 value from the blower door test should not exceed 1.5 per hour. In leaky buildings, most of the air flows uncontrolled through joints and gaps without passing the heat exchanger. Heat recovery then only acts on a fraction of the air change and the investment does not pay off.

What is the difference between central and decentralised ventilation?

A central system has one ventilation unit and distributes supply and extract air via a duct network throughout the building. Semi-decentralised units each serve one dwelling with their own heat exchanger and a short duct network. Central systems with counterflow heat exchangers achieve the highest heat recovery efficiencies of up to 92 %; decentralised systems are easier to retrofit and can be controlled separately per apartment.

Which standard governs residential ventilation in Austria?

In Austria, ÖNORM H 6038 specifies the design and installation of comfort ventilation in residential buildings, including air volumes, acoustic protection and maintenance. ÖNORM EN 16798-3 applies to non-residential buildings. Performance testing of ventilation units follows ÖNORM EN 13141. The design air change rate of 0.4 per hour comes from H 6038.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Kritische Messpunkte: (1) Stromzähler Lüftungsgerät, (2) Temperaturfühler Zuluft/Abluft/Außen, (3) CO2-Sensor in Hauptraum für DCV-Steuerung, (4) Filterdruck. Damit ist Energiekennwert Lüftung pro m² überwachbar.

All measures