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Air Leakage v Ventilation - Striking the Balance

Posted by Sam Tonge on 15 August 2017 at 2:03 pm

Why is air leakage a problem?

Air leakage is widely accepted as a major cause of thermal inefficiency within many of our homes in the UK, accounting for 30% of total heat loss on average. The uncontrolled flow of air through small gaps in our properties can rack up our utility bills as well as being very uncomfortable for occupants of these draughty houses! Higher CO₂ emissions also result from this lack of airtightness, as any heat produced will quickly escape to the outside. However too much airtightness can result in poor air quality within the home, meaning ventilation becomes a requirement. So how does controlled ventilation differ from uncontrolled air leakage?

There are two ways in which air leakage occurs within some properties.  Cold air can find its way into the home through gaps in the walls, floors and ceilings, resulting in cold draughts and even condensation problems. Conversely, leaking of warm air produced inside the house through these gaps is known as exfiltration, which leads to a lot of wasted energy.

Can my home become too airtight?

Improving airtightness is not just about filling in gaps, but improving design and construction through draught-proofing, double-glazing and various forms of ventilation. In other words, ‘build tight, ventilate right’.

It is worth noting that too much airtightness within a building can also be problematic, resulting in poor air quality, internal damage, e.g. mould, as well as health problems for the occupants. However this can be alleviated by controlling airflow patterns through your home, which is best achieved through a carefully-designed ventilation system. The key difference from air leakage is that with ventilation the openings are purpose-built and placed in well thought through locations, ensuring you feel comfortable within your home.  

How to achieve a balance

With ventilation you can control the amount of air moving in or out of your home, providing you with the ability to modify airflow patterns depending on your needs. This can include localised extractor fans to remove excess moisture in damp rooms, e.g. bathrooms and kitchens, alongside well-placed trickle vents in other areas of the home.

In cases where dwellings are very airtight, a mechanical ventilation heat recovery system is recommended to ensure good air quality and efficient use of central heating. With this method, fresh air is drawn from outside, warmed in the heat exchanger and delivered to cooler room such as the lounge and bedrooms. Read our information pages to learn more about different methods of ventilation.

However generally speaking, most homes are not this airtight, meaning air leakage still persists as a common problem. In most cases, a combination of draught proofing and insulation combined with trickle vents, localised extractor fans and the traditional opening of the windows are the best way to establish a balance between airtightness and a well-ventilated home.


More information about ventilation and draughts on YouGen.

Find a ventilation and draught proofing installer

Need help with any Jargon?



Image credit: Jason Jasmic

About the author:

Sam has contributed to our blog since 2016 and previously worked for the National Energy Foundation.

He became interested in green energy after completing a degree in Geography (BSc) at Royal Holloway, University of London. 

Sam is passionate about renewable energy and is committed to spreading the word about the role it plays in delivering environmental sustainability. 

If you have a question about anything in the above blog, please ask it in the comments section below.

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1 comments - read them below or add one

Zero Is More

Zero Is MoreComment left on: 31 August 2017 at 8:33 pm

After a passiv-haus refurbishment, my family mutinied against closed windows and heat-recovery ventillation. After 2 years of argueing about it, we settled on a stand-off. You open the windows and I will switch 0ff the space heating. both sides called each other's bluff - open window ventillation and no space heating. Imagine my surprise when the house answered with a steady 18 °C through the winter, dropping to 16 °C after mid-night and recovering again at 0730 when the people and systems awake. We live happily like that now, wearing sweaters (like our parents did) and bragging to any and all about our achievement - not mentioning that it happened by chance. But seriously, I believe we in temporate climes have imported continental solutions that we dont need. For us, passiv-haus means no moving systems - no central heating and no mechanical ventillation/heat recovery.

Not bliss, but nobody is ever blissfull in Scotland.

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