A ventilation system's primary objective is to maintain proper indoor air quality and air exchange. When mechanical ventilation with heat recovery is used, the air is additionally filtered to eliminate impurities before it is delivered to the rooms.
The vast majority of HRV units currently available on the market feature supply and exhaust filters, which allow air to be purified both as it enters the home and as it leaves it.
In order to protect your house from pollution, you should ensure that the outside air is filtered before it enters the rooms, i.e. by using mechanical ventilation with heat recovery.
Our mechanical ventilation system already has MVHR filters, so are we protected from smog in that case? No, not exactly. It is important which filtration device our system is equipped with. Typically, HRV units are fitted with coarse pre-filters, i.e. filters with a medium filtration efficiency that are unable to capture particles as small as particulate matter (PM). This raises the question: Why aren't "stronger" HRV filters used in heat recovery ventilators?
It goes without saying that the higher the efficiency of the air filter, the higher the price. The MVHR filter replacement is one of the most important factors contributing to the operating cost of the system.
You should remember that the heat recovery ventilator has a pair of filters that need to be replaced regularly. It might need to be done every 3-6 months, or more often if the air pollution levels are high. Equipping the heat recovery ventilation with a more expensive set of fine filters would increase the operating costs of the entire HRV system.
Because filters are so expensive, customers may decide to either change them not frequently enough (e.g. by "cleaning" them) or manufacture their own instead of purchasing the recommended model.
Since we are a manufacturer, we can’t be neutral in this debate. Yet, the truth is that a filter is an essential component of the air handling unit. HRV performance also depends on the type of filter it is equipped with. Tests of a unit are conducted with a specific filter. This means that all the device parameters we determine – capacity, compression ratio, heat recovery, etc. – are determined for the heat recovery ventilator with a specific, clean filter.
Replacing the filter with a non-brand one can significantly affect the capacity of our ventilation system. For example, it may turn out that the air handling unit will have x% worse capacity because we have used a filter not recommended by the manufacturer.
Also, using non-original spare parts may void the manufacturer's warranty (please check the heat recovery ventilator warranty terms and conditions), e.g. “The warranty shall cease to be valid when the user makes changes to the subject of the warranty and when spare parts other than those recommended by the manufacturer are used."
Therefore, we recommend purchasing only dedicated MVHR Filters.
Another reason for equipping the heat recovery ventilator with filters with lower filtration efficiency is the problem of generating resistance in the device. Filters increase airflow resistance, which in turn increases the amount of electricity needed to operate MVHR / HRV systems.
If the heat recovery ventilator was fitted with fine filters, would also require using more powerful fans, the air handling unit would need to be larger, and the cost of the heat recovery unit would be higher.
An MVHR manufacturer must find a golden mean – a kind of compromise in selecting the optimum air filter model to ensure adequate indoor air quality parameters, while not generating significant resistance in the system.
Until a few years ago, G4 class filters were the industry's standards, complied with the now outdated EN 779 standard. There is now a new standard, ISO 16890, where the classification of filters is based on the method of filtration determined by giving the particle size as the particulate matter it can filter and its efficiency as a percentage.
Heat recovery ventilation air handling units of the PremAIR and SlimAIR series are equipped with ISO Coarse 70% HRV filters and, optionally, we offer ISO ePM1 55% fine filters.
The heat recovery ventilation cleans the air of impurities, but if it is not equipped with fine filters – it will not protect us from smog. According to a comparison developed by the Eurovent association (see Table 1), a filter must be at least of F7 class according to the old standard in order to be defined as an "anti-smog" filter (filtering PM2.5 and PM10 particles).
| EN 779 :2012 | EN ISO 16890-1:2016 |
| M5 | ePM10 ≥ 50 |
| F7 | ePM2.5 ≥ 65 |
| F7 | ePM1 ≥ 50 |
| F9 | ePM1 ≥ 80 |
Table 1. Filter class conversion proposed by Eurovent
However, F7 filters or ePM1 ≥ 50% filters according to the new standard are usually available on the market as additional accessories, and the heat recovery ventilator is delivered with coarse pre-filters.
When living or wishing to live in an area where air pollution is very high, we recommend:
*If the heat recovery ventilator model we have chosen cannot be equipped with HRV filters with a higher filtration efficiency, e.g. due to excessive resistance, we recommend installation of a duct filter.
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