EC Fans & Specific Fan Power for Passivhaus MVHR Units

Driven by growing awareness of their environmental and economic benefits, the demand for Passivhaus buildings is increasing in the UK. The Passivhaus standard provides a benchmark for energy-efficient and sustainable building design. We’ve covered an introductory article on Passivhaus previously which covered broader topics including airtightness, insulation, thermal bridges, window performance, renewable energy, emissions, tiers of compliance, and EnerPHit retrofit standard. Read more in our article “Energy Efficient Fans, MVHR and The Passivhaus Standard”.

This complementary article develops that introductory article for those of you who are looking for more technical, product-aligned information, and focused on SFP and MVHR compliance specifically. So let’s just touch on the basics slightly.

Back to the Passivhaus certification. New and existing buildings can achieve Passivhaus certification by meeting a strict set of performance criteria. One of these is the use of Mechanical Ventilation with Heat Recovery (MVHR) units to reduce energy consumption and maintain high indoor air quality. For an MVHR unit to be certified by the Passivhaus Institute, it must meet specific technical standards, including requirements for specific fan power (SFP) and heat recovery efficiency.

Reminder: What Is An MVHR? 

So, what do MVHRs do? Put simply, MVHR systems are ventilation systems, that extract stale air from the building and draw in, fresh, filtered air from outside. As air is exchanged, heat is recovered from the outgoing air and used to pre-heat or pre-cool the new, incoming fresh air, via a heat exchanger. This process reduces the need for space heating or cooling and maintains a good indoor environment, a key priority for Passivhaus buildings. So, in short, MVHR units contribute to the overall sustainability goals of Passivhaus buildings.

Specific Fan Power for Passivhaus MVHR Units

It’s calculated as:

SFP = total fan power (in Watts) ÷ air volume flow rate (in m³/s)

In the context of the Passivhaus certification, SFP is often expressed as Watts per cubic metre per hour (W/m³/h). A lower value indicates a more energy-efficient fan system.

To meet Passivhaus certification standards, MVHR units must not exceed an SFP of:

0.45 W/m³/h

This means the fan system should consume no more than 0.45 Watts for every cubic metre of air moved per hour.

It’s important to note that actual UK compliance (e.g., SAP or Building Regs) may use different benchmarks like ≤0.8 W/(L/s) depending on the system setup, that’s why it’s best to have a chat with us to ensure we’re always working on the benchmarks that meet your project goals.

Other MVHR Design Considerations (Outside of Just SFP)

Several key factors should be considered when designing MVHR units. This includes ductwork, optimising fan design, system pressure, and control strategies. Finding the right balance between sufficient airflow and low fan energy consumption is a challenge at times, but choosing the right partner can help to alleviate these issues quickly.

As experts in all aspects of air movement, with extensive knowledge in the MVHR market, we’d recommend initially looking at the Rosenberg Group range of forward curved fans manufactured by Ecofit, as a strong option for Passivhaus-aligned projects. The Rosenberg Group range offers energy-efficient, low-noise fans that support high-performance ventilation design in line with certification standards. Get in touch with a member of our pre-sales team to discuss all aspects of MVHR if you’re looking for more information on the Rosenberg Group range of fans exclusively available from Axair in the UK market.