• Myth Buster

    Myth Buster

    MVHR has attracted a number of myths.
    See what people come up with...

Common myths about MVHR systems

You cannot open your windows with MVHR

This myth stems from the operation of air conditioning systems, which actively (electrically) heat or cool with re-cycling of air. With each air cycle heat or cold is introduced. The opening of windows breaks this cycle and renders the system useless, whilst all the kWh’s of energy used for heating or cooling are being lost.

MVHR operates in a completely different way, as the air is not re-cycled and is heated or cooled passively, without heating or cooling elements (unless a post heater is installed).
So, feel free to open windows and doors. In summer you can then turn down the MVHR. In the cold time of the year, you will want to limit the opening of windows to retain the heat inside.

A Passivhaus/ Passive House is a dwelling without heating

This is a very common mis-conception. About half of the European certified Passivhaus dwellings have a central heating system; The rest still needs a backup heater, e.g. post heater in the MVHR system, as every house has heat losses, even if they are minimal. In cold periods when there is no solar gains for a couple of days, some heat input is needed to keep the internal temperatures at a comfortable level.
If you endeavour to build a house without central heating, please talk to us in the early design stage about this. We are happy to assist you in designing the MVHR system to meet your needs.

The MVHR will distribute the heat from wood stoves around the house

Although our high-performance MVHR systems cut out almost all ventilation losses, the system will in itself not level out the temperatures between heated and un-heated rooms. Temperature differences of 4-10 degrees between rooms can still be achieved, depending on the ventilation volumes and internal heat transfer.
We can offer experimental ways of heat distribution.
Please talk to us in the early design stage if you intend to use the MVHR for heat distribution.

MVHR costs a fortune to run

Our MVHR systems for an average 3 bedroom dwelling typically use about 25-40W. This is an energy expenditure of £26 -£50 per year.
Compared to about 30% heating energy savings if the house is relatively airtight, this is not much.

You need to pay a lot for new filters

We want to offer filters to our customers at the cheapest prices possible, as a ‘thank you’ for choosing us.
If you look at soiled filters, remember that this is the pollution that you didn’t have to filter through your lungs.

A too clean indoor environment is not healthy.

It is true that our bodies usually have the amazing capability to build up anti-bodies for a natural immunisation, when in contact with bacteria and viruses. Unless in quarantine, we cannot avoid such exposure anyway when being out and about.
However in modern society, our bodies are under increased stress from an onslaught of harmful substances and particles. In modern dwellings these can be 2-50 times more than in outdoor air. To reduce these indoor amounts by good filtration, will give our bodies a well deserved break/ reduction in stress.

MVHR causes sickness

Again this myth originates from some of the experiences with air conditioning systems, which had not been maintained properly. As air conditioning is based on the (re-)cycling of air, bacteria that are being picked up can be distributed around. Also it is important to clean A/C systems and change filters regularly, to avoid the germination & growth of mould, harmful bacteria and pathogens inside the system, as these will be re-introduced into the building.

MVHR in contrast does not re-cycle air. In high-quality systems, all contaminated extract air is completely exhausted and is not in contact with the fresh air which is being supplied to the house. Thus it helps creating a healthy environment.

I don't want to depend on a mechanical system

As much as we support the endeavour to make house technology as simple as possible, we see MVHR as the second best ventilation option; only that there is no better one…
Natural ventilation in modern dwellings just does not seem to work without user-operated cross-ventilation. See the article on air quality in modern homes (Info/Research…)