Specific Fan Power (SFP)

Specific fan power (SFP) is the electricity that the fans of a ventilation unit draw for every cubic metre of air they move each hour. It is written in Wh/m³, which is the same as W/(m³/h). Datasheets and regulations use several names and units for the same idea, so compare them with care. The number tells you how much electricity a unit needs to move a given volume of air. It is one of the criteria on the Passive House Institute certificates for heat recovery ventilation units, a passive house component class.

What does specific fan power measure?

SFP compares electrical power with airflow. A unit that draws 45 W while moving 100 m³/h has an SFP of 0.45 Wh/m³, because 45 divided by 100 gives 0.45. A lower value means the unit moves the same air with less electricity. The figure belongs to the unit. Two units sized for the same airflow can have very different values.

The number is only meaningful with its test conditions. Each value is stated at a particular airflow and external pressure, and a certificate may list several models, each with its own result. When you compare two units, check that both figures were measured at a similar airflow and pressure.

Which units and names does SFP use?

The same idea appears under three unit systems. Check which one a datasheet uses before you compare two figures.

Name	Unit	Where it appears
Specific electric power (Pel,spec)	Wh/m³	Passive House Institute certificates
Specific power input (SPI)	W/(m³/h)	Regulation (EU) No 1253/2014, Annex I point 1(13)
Internal specific fan power (SFPint)	W/(m³/s)	Regulation (EU) No 1253/2014, Annex I point 1(12)

Wh/m³ and W/(m³/h) are numerically equal. One hour has 3,600 seconds, so a value in W/(m³/s) is 3,600 times the value in W/(m³/h). For example, 0.45 Wh/m³ is 1,620 W/(m³/s). The two regulation quantities are not the same measurement. SPI is power divided by flow at a reference point. SFPint is the internal pressure drop of the ventilation components divided by the fan efficiency, for a reference configuration.

How do Passive House certificates state SFP for a house-size unit?

The Passive House Institute (PHI) certifies ventilation units as components and publishes the results in its component database. Each certificate lists the main criteria that the product met. This article read two certificates for units below 600 m³/h, the size range of a single-family house. Both are for the Zehnder ComfoAir Q350, the first with a heat recovery ventilation (HRV) core and the second with an energy recovery (ERV) core. The PHI criteria document itself could not be opened, so the limits below are those printed on these certificates.

Criterion on the certificate	Limit
Heat recovery rate (ηHR)	at least 75 %
Specific electric power (Pel,spec)	at most 0.45 Wh/m³
Leakage	below 3 %
Comfort	supply air at least 16.5 °C at an outdoor temperature of −10 °C

Each certificate states that it was awarded because the product met these main criteria. The electric power limit is therefore a pass or fail gate, not only a figure for ranking units. Both certificates are valid until 31 December 2026, so check the database for a newer entry before you rely on them.

Model (component ID)	Airflow range (m³/h)	Pel,spec (Wh/m³)	Heat recovery rate
Zehnder ComfoAir Q350 HRV (0956vs03)	70 to 270	0.24	91 %
Zehnder ComfoAir Q350 ERV (1006vs03)	70 to 270	0.25	92 %

Both models sit at about half of the limit. A third certificate covers a ComfoAir Q350 ERV with humidity recovery (1438vs05). It uses a cooling recovery criterion of at least 70 % instead of the heat recovery rate. It keeps the same 0.45 Wh/m³ limit and reports 0.26 Wh/m³.

Under what conditions is the house-size value measured?

The two ComfoAir Q350 certificates state the same method. The power of the whole device is measured at an external pressure of 100 Pa. The certificates give 50 Pa each for the intake and the outlet. The figure includes the power for operation and control, but not for frost protection.

Three other facts on the same certificates affect what you get at home. At −15 °C outdoors, the frost protection strategy reduces the airflow. It falls to about 200 m³/h for the HRV and about 220 m³/h for the ERV. The HRV certificate gives a standby consumption of 1.30 W and notes that the target value of 1 W was exceeded. A house with long ducts or dirty filters may have a different pressure from the test. This article does not quantify that effect.

What SFP values do larger units reach?

Units above 600 m³/h are a secondary case for a family house, for example in a block of flats or a small commercial building. Two PHI certificates for such units use the same 0.45 Wh/m³ limit and the same 75 % heat recovery limit. Their measured values sit close to the limit. The Nuaire XPC65 reaches 0.40 Wh/m³ at 430 to 1,390 m³/h with a heat recovery rate of 84 %, measured at 243 Pa. The Zehnder EVERKIT series, measured to the residential requirements at 180 to 246 Pa, reaches 0.43 to 0.45 Wh/m³.

Model	Airflow range (m³/h)	Pel,spec (Wh/m³)	Heat recovery rate
Zehnder EVERKIT 1500	560 to 900	0.45	83 %
Zehnder EVERKIT 3000	900 to 2,100	0.43	83 %
Zehnder EVERKIT 5000	2,100 to 2,600	0.43	86 %

These certificates also list a performance number, with a recommended value of 10. The certificate notes that the EVERKIT 1500 did not achieve 10.0 and reaches 9.5. A certificate can pass the electric power criterion and still fall short on another measure. Read the full list of criteria, not one number.

The Nuaire certificate states a tested external pressure of 243 Pa. It then notes that the real available pressure with installed filters is 174 Pa, and that additional components reduce it further. The Zehnder table shows the same pattern. Tested external pressures of 180 to 246 Pa correspond to actual available pressures of 142 to 214 Pa after the filter pressure drop.

How does SFP differ from heat recovery efficiency?

Both figures appear on the same certificate, but they answer different questions. Heat recovery efficiency says how much heat is kept from the exhaust air. SFP says how much electricity is spent moving the air.

	Specific fan power	Heat recovery efficiency
What it measures	Electricity used per unit of airflow	Share of heat recovered from the exhaust air
Unit	Wh/m³	%
Certificate limit	at most 0.45 Wh/m³	at least 75 %
Effect on the house	Electricity used to move the air	Heat needed to warm the incoming fresh air

A unit can meet one criterion and miss the other, so both belong in any comparison. A balanced ventilation system has a supply fan and an extract fan. On the certificates, the electric power is measured for the whole device including its controls, not for one fan alone.

What does the EU ecodesign regulation say about fan power?

Commission Regulation (EU) No 1253/2014 sets ecodesign requirements for ventilation units. Article 2 splits them into two groups. A residential ventilation unit (RVU) has a maximum flow rate of up to 250 m³/h. It may also have 250 to 1,000 m³/h if the manufacturer declares exclusive residential use. A non-residential ventilation unit (NRVU) is any larger unit, or one in that middle range without the residential declaration. The requirements apply from 1 January 2016 and from 1 January 2018 (Article 3).

The regulation does not set an SPI limit for residential units. Annex II instead limits the specific energy consumption (SEC) of an RVU. The SEC limit is 0 kWh/(m².a) from 1 January 2016 and −20 kWh/(m².a) from 1 January 2018. SPI enters the SEC calculation, and the Annex VIII equation writes it in kW/(m³/h), while Annex I defines it in W/(m³/h). Annex IV requires the manufacturer to publish the SPI in W/(m³/h) for each RVU model, so you can read it from the product information.

For non-residential units, Annex III sets a maximum SFPint in W/(m³/s) as a formula. The result depends on the heat recovery type, the nominal flow rate, the efficiency bonus and the filter correction, so it is not one number. Annex VII lists benchmarks that are not requirements. The Passive House certificates above and this regulation are separate schemes, and a unit may meet one and not the other.

How should a buyer use the SFP figure?

• Ask for the certificate or the database entry, not only the figure on a brochure.
• Compare units at the same airflow and external pressure, since the certified value depends on both.
• Check the unit of each figure: Wh/m³ and W/(m³/h) are equal, and W/(m³/s) is 3,600 times larger.
• Ask the designer for the pressure that the ducts and filters will actually impose.
• Check the airflow range on the certificate and whether the unit's airflow falls within the range it was tested for.

Does SFP matter outside Passive House certification?

The regulation requires the SPI in the product information for residential units. It can therefore appear on datasheets of units without a Passive House certificate. This article does not quote any Slovak building regulation, and any legal requirement should be checked against the current text before it is relied on.