A fan's power in watts and electrical energy in kilowatt-hours are not the same thing. To understand a heat-recovery ventilation unit's consumption, you need to know its actual average power and the time it spends in different operating modes. The maximum power on the label does not automatically represent continuous annual consumption. You also need to distinguish the fans from additional heating and other functions. A clear calculation lets you assess your own data without a universal promise of what every household will pay.
First, establish the units
A watt describes power at a particular moment. A kilowatt-hour is an amount of energy accumulated over time. When power is given in watts, calculate energy by multiplying it by hours and dividing by a thousand. This is an arithmetic relationship, not a measure of the heat-recovery unit's efficiency. Your bill charges for energy under your contract terms, not for the equipment model number itself.
If power varies, you need separate time periods or an actual energy measurement. A single instantaneous value does not describe the whole year. Do not draw conclusions about summer operation from one cold day. Likewise, do not compare consumption in two houses without knowing the airflows and operating hours: a lower figure may mean a smaller task, not better equipment.
An illustrative example with constant power
Suppose, purely for illustration, that the combined average power of both fans were 40 W and remained constant around the clock. Daily energy would be 40 × 24 ÷ 1000 = 0,96 kWh. Over 365 days, it would be 350,4 kWh. This is not a promise for a specific model or an average applicable to every house. The example only demonstrates the correct relationship between units and time.
To obtain a monetary amount, multiply energy by your actual current tariff, taking your contract structure into account. This article deliberately does not invent a tariff. If different time bands apply, divide the periods accordingly. Standing charges are also not the same as additional energy consumed by a particular appliance.
When several modes are used during the day
Suppose, in an illustrative case, the unit operates for 20 hours at 30 W and for 4 hours at 60 W of combined fan power. Energy would be 20 × 30 ÷ 1000 + 4 × 60 ÷ 1000 = 0,84 kWh per day. This result applies only to the stated assumptions. A real house needs actual data, not smaller figures chosen to make an offer look more attractive.
It matters whether the controller actually displays measured power or a calculated estimate. The Komfovent C6M user manual shows an example of a particular control system's functions, but the nature of the data may differ in other models. Ask for an explanation of exactly what you see on the screen and the limitations of the reading.
Calculate additional heating separately
If the unit has an electric heater, its power must not be confused with fan power. A meter for the whole house or appliance may include both. Higher winter consumption therefore does not necessarily mean that fan consumption has increased by the same amount. Establish which function operated and for how long.
The Komfovent installation manual discusses the heating and protection arrangements of specific designs. Check the documents and configuration for your own model. Stating a heating element's maximum power does not mean that it operates at that level continuously. Energy depends on the actual duty cycle and conditions.
Airflow and resistance matter
The same unit may have a different operating point in a different system. Filters, ducts and adjustment all have an influence. Catalogue data must therefore be assessed under the conditions specified for it. The DOE ventilation overview helps explain that the unit performs a task within the overall system rather than operating independently of its connections.
For this reason, do not reduce airflow simply to improve the bill without checking demand. Adequate air exchange is the function being delivered. Sensible savings involve justified operating modes, well-maintained filters and fewer unnecessary losses, not switching off ventilation in an occupied room. Lower electricity use without the required result is not an equivalent efficiency comparison.
How to measure safely
Electrical measurement must suit the connection type and the appliance's safety requirements. If the unit is permanently wired or obtaining data requires work in the electrical distribution board, contact a qualified specialist. Do not dismantle the installation yourself merely to investigate consumption. Not every domestic adapter is suitable for every load or installation location.
When measuring, choose a sufficiently long period and record the operating modes. If you want fan energy alone, it must be clear whether additional functions have been separated. If this cannot be done, call the result the unit's total energy use, not fan consumption alone. An accurate description prevents mistaken conclusions and inappropriate comparisons between two offers.
A controller percentage is not a power measurement in watts
A display stating that a fan runs at a certain percentage does not necessarily mean the same percentage of its maximum electrical power. This depends on the control logic and particular operating point. In a calculation, you therefore cannot simply multiply rated power by the displayed operating setting and treat it as an accurate measurement. You need a documented power reading, appropriate manufacturer's curves or safely measured energy.
If comparing periods before and after a filter change, record the airflow setting too. Otherwise, the changed figure may be related to different use. The same applies to a software update or a new weekly schedule. Even a real energy meter does not explain the cause without context: it confirms the quantity but does not prove what changed it.
For an annual assessment, it is worth having at least information on seasonal differences rather than a short sample in favourable weather. If that period is not yet available, call the result an indicative forecast and state its assumptions. Do not rename a forecast as actual annual consumption simply because the final table looks attractive.
What to provide for diagnosis
Prepare the model, airflow settings, measurement period and measured energy. State the outdoor conditions and filter maintenance date. If consumption changed suddenly, note what was changed beforehand. The house's total monthly bill alone cannot reliably establish how much was consumed specifically by ventilation.
Read more about maintenance in this article, and the information can be submitted in an enquiry. A correct conclusion has clear assumptions, units and measurement boundaries. It should not promise identical annual costs for different houses or confuse the entire heat-recovery unit with its fans alone.
Information sources
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