Covid puts the focus on air quality in our homes

What are the best systems to employ in your home
Covid puts the focus on air quality in our homes

MVHR House Drawing_v1

Dear Kieran, I am building a new house next autumn and I have been told that I will probably need a ventilation system. To be honest I have no idea what is available or what I should choose. Can you please give me some idea of what you would advise here?
Many thanks Mags, Macroom

Dear Mags, Many thanks for your question and what a great topic to discuss! Given that we are still (unfortunately) in the middle of a pandemic one thing we are all becoming much more conscious of is the quality of the air that we breathe. Whether it is opting for country air instead of city air, outdoor air instead of indoor air or longing for better ventilated indoor areas, it’s all up for discussion now.

Kieran McCarthy: 'In the past, our only experience of mechanical ventilation has been the fan that comes on when you hit the bathroom light in an apartment'.

Kieran McCarthy: 'In the past, our only experience of mechanical ventilation has been the fan that comes on when you hit the bathroom light in an apartment'.

As it turns out, ventilation of dwellings particularly new builds and deep retrofits of existing houses has advanced considerably even in the last 8-10 years. Much of this has been in conjunction with an improvement in the heat loss control of houses where air leakage (drafts) have been all but eliminated through airtightness measures (placing tapes and membranes to control drafts). 

The new airtightness levels of houses have brought about the need and advent of centralised mechanical ventilation. In the past, our only experience of mechanical ventilation has been the fan that comes on when you hit the bathroom light in an apartment - and wakes everyone up at 3 o’clock in the morning - but in truth there have been great strides in ventilation systems since then. These systems fall broadly into two categories, demand control ventilation and full heat recovery ventilation. Let’s consider these separately.

Demand control ventilation is a system whereby moisture laden air is extracted from your wet room areas (bathrooms, utility rooms, kitchens) and fresh air is drawn in to replace this moist air through either vents in your windows or moisture-controlled vents in your walls.

These systems are also sensitive to CO2 and a variety of other noxious gases and, as they draw in fresh air, there is a general improvement in the air quality of the adjacent rooms from whose window vents the fresh air replacement is drawn.

Ventilation and indeed airtightness are great long-term investments as they reduce heat loss and improve air quality.

Ventilation and indeed airtightness are great long-term investments as they reduce heat loss and improve air quality.

Full heat recovery ventilation is a step-up again where there is a centralised ventilation unit that is constantly managing the air quality of all habitable rooms. As it removes stale air from rooms it removes the heat from the stale air and uses this heat to preheat incoming replacement fresh air, so heat isn’t substantially lost.

Clearly, this is particularly beneficial in winter when indoor air is maintained at a higher temperature to outdoor air. The benefits of demand control ventilation is that it is quite cost-effective and the amount of builders work (coring holes, boxing-out pipes etc) is small so hence the overall system is providing a level of active ventilation without a very prohibitive cost. 

The full heat recovery ventilation system costs a lot more to begin with, and then there is a considerable volume of builders’ work and indeed space required to house the central ventilation unit so it can cost nearly twice as much when all considered. The HRV system has the added benefits of actually heating the incoming air to reduce heat loss (particularly in winter) and as it is always on it provides a greater level of air quality improvement.

Both systems require an improvement in airtightness for efficient use (HRV even more so) but in a new build home (or even in a deep retrofit) this is now a given to comply with building regulations in any case. Indeed, at the low levels of airtightness in a new build home you will likely need a controlled ventilation system to manage air quality as there will be little avenue for this in the absence of the air leakage (drafts) we became accustomed to of old.

All in all, though yet another cost to be considered in the budgeting of your new home build, ventilation and indeed airtightness are great long-term investments as they reduce heat loss and improve air quality. Given that we are all reimagining what life will be like post-pandemic, air quality is now firmly in focus and indeed is now being actively considered for factories, schools and likely all habitable buildings going forward.

Civil engineer Kieran McCarthy is founder and Design & Build Director with KMC Homes. He is a co-presenter of the popular RTÉ show Cheap Irish Houses.

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