Consider mechanical ventilation with heat recovery for good indoor air quality and energy efficiency.
By Sarah Warwick
Every home needs fresh air to come into the building from outside for you to breathe, and for the safe operation of combustion appliances. It’s also vital that stale and damp air and pollutants are removed – both for your health, and the integrity of the building. Opening windows and doors – so-called purge ventilation – teamed with extractor fans in kitchens and bathrooms will do the job, but of course causes heat loss.
To ensure that you are saving energy but also creating a healthy home, it’s vital to consider how the house is ventilated. Whole mechanical ventilation with heat recovery (MVHR) systems are a solution. They exchange stale air for fresh air, and recover heat in the process.
An MVHR system will extract the warm, moist air from rooms such as kitchens and bathrooms. This is done through a concealed duct system. The air is passed through a heat exchanger then ducted outside. Fresh air from outside is drawn in and passed through the heat exchanger, which warms it, and it’s then ducted to the living rooms and bedrooms. Some systems have a feature so that when it’s warm outside, the air can bypass the heat exchanger to help keep the house cool.
The systems often have two speeds, so when the kitchen and bathrooms are being used – and producing lots of moisture – the extraction rate can be boosted.
If you’ve built an energy efficient house, then the system can meet part of the heating needs of your home, as well as helping to distribute the heat. If you are building to Passivhaus standard, MVHR will contribute to satisfying the requirements. The systems can be combined with ground air heat exchangers.
Many systems come with air filters, so they’re helpful in preventing potential allergens entering the house.
An MVHR system will need regular maintenance. The system needs to be kept in balance in terms of the supply and extraction of air. Filters, grilles, fans and heat exchangers need to be kept clean, too.
The system’s heat exchanger is generally fitted in the loft, although it could also be installed in a void in the eaves or ceiling, or a cupboard in the kitchen or utility room, or even in the garage. Consideration will need to be given to the positioning of the concealed ducting at planning stage.
‘Although it can be fitted by a competent DIYer, changes to the building regulations in October 2010 mean that ventilation provision in new houses must be commissioned by a suitably qualified person,’ says Chris Marriott, Managing Director of ADM Systems. ‘You should always make sure that your system provider is capable of offering a qualified installation and commissioning service or at the very least a comprehensive installation guide. This can be supplemented with a site support service which includes a qualified engineer visiting site to offer help and guidance to those who are undertaking the installation. However, whichever approach is taken, the system will need to be commissioned by a qualified person using calibrated test equipment.’
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