Breathe easy

Phil Harrison of EnviroVent offers advice on the best ways to achieve optimum ventilation and energy efficiency when upgrading the home or undertaking a self-build


growing number of homeowners and self-builders are realising that ventilation is an essential part of achieving a healthy as well as energy efficient home.

The most visible signs of a lack of ventilation are condensation and mould growth, which is unsightly, while the spores released by mould can exacerbate health issues such as asthma. As self- builders are building to greater levels of airtightness they are turning to a whole house ventilation approach. There are several options available when it comes to whole house ventilation, all of which comply with current Building Regulations. However, there are a number of factors to take into consideration including the airtightness of the property, number of occupants, the type and age of property, and its potential space restrictions.

The entry-level option would be System 1: intermittent extract fans with background ventilation – usually trickle vents in the windows. The extract fans would be located in the wet zones of the property – the kitchen, utility room, bathrooms and en suites. The potential downside is that this is not the most energy efficient method, owing to the heat loss incurred through the extract fans.

Many self-builders also don’t like the aesthetics of trickle vents in the windows and some extract fans can be noisy, especially if they are not regularly maintained. There are low noise options on the market which operate with exceptional performance and the minimal sound levels.

Option two is passive stack ventilation. This is a non-mechanical form of ventilation which works through vents that are located in wet zones and uses the principle of convection to allow the movement of air via currents. Background vents need to be installed in conjunction with passive stack. The downside to passive stack ventilation is that the airflow rate is weather dependant, which means there is a risk of either over

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ventilating or under ventilating. The third option is System 3: mechanical extract ventilation (MEV). This is a continuous extract system designed with multiple extract points to draw moisture-laden air out of the wet zones such as bathrooms and kitchens through a central unit before being ducted out to atmosphere. This negates the requirement for numerous extract fans throughout the property and can therefore be a lower cost and quieter option if the property has a large number of wet rooms. As with individual extract fans, trickle vents need to be installed in order to meet the whole house ventilation rate.

A better solution for self-builders is System 4: mechanical ventilation with heat recovery (MVHR). Heat recovery systems work by extracting the stale, moist air out of the wet rooms, which is ducted to a central unit, normally located in a loft space of a house or a utility room or cupboard in an apartment. This extracted air passes over a heat exchanger before being ducted

to outside.

At the same time, fresh air is drawn into the unit from outside via a filter and is warmed by a high efficiency heat exchange cell. This tempered, fresh air is then delivered through supply vents into the living, dining and bedroom areas. This system maintains a stable humidity level, free from condensation and mould. Anyone with asthma or other respiratory problems should also find this method of ventilation much more beneficial. Heat recovery systems require no

background ventilators or extract fans, in fact, MVHR relies on a high level of airtightness throughout the property. That is why, with homes being built to greater levels of airtightness, energy-conscious self-builders are choosing heat recovery (MVHR) for all-year-round efficient and balanced ventilation.

Ultimately for self-builders who are

energy-conscious and are looking to design and build to specific construction standards such as Passivhaus, MVHR is one of the few options to satisfy the requirements. 39

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