Draughtproofing v. Ventilation

Home Health Check webinar

by Anaeka Kellay from Carbon Coop

As we’re spending such a lot of time at home during this pandemic, and because the coronavirus impacts the respiratory system, and because I always thought that a draughty house, like mine, was also a ventilated house I thought this, my first ever webinar would be particularly interesting.


Firstly, it is quite clear that the way in which all the features (ventilation, heating, lighting and appliances and people etc) of a house interact is quite complicated and that making changes to one aspect will alter the impact on other aspects eg more people will create more moisture and will impact on the number of lights, appliance use and may require more heating and ventilation.


However, Carbon Coop emphasize that they believe in a Fabric First approach ie. that you make your house as energy efficient as possible, as illustrated by this energy hierarchy. This means locating and blocking up all the draughts.

Secondly, you need to ensure that air that is flowing into the house enters, and leaves, where you want it to. So, you need to ensure that your home has adequate ventilation, this makes sure that the whole house feels comfortable in terms of temperature and humidity, otherwise you will get damp and mould building up in certain areas. This film from the UK Centre for Moisture in Buildings (UKCMB) explains this really well.


Film: Managing damp and mould in your home

The optimum temperature of your home is 18-21oC (18oC in the bedroom and 21oC in the sitting room) and relative humidity between 40-60%. You can measure these with a combined digital device, these were recommended by Carbon Coop, “they are not pro level but very good for the price, accurate to 1-3% humidity and 0.5 on temp”. Or you could try to make your own hygrometer – perhaps something to have a go at with the kids! (NB. not recommended by Carbon Coop).

And finally, you just need to figure out what you are going to do about it!

What you can do is governed by building standards, though this are not particularly stringent. The Passive House (or Passiv Haus) standards are the highest possible for new build, while the ideal retrofit measure are the EnerPHit standards.

Ventilation Options


“Any retrofit project that does not consider ventilation is a condensation project” Colin King, Building Research Establishment

  • Construction ventilation in subfloors, roofs and certain walls – your architect/ builder will install this and you need to keep them open!


  • Natural ventilation – relying on opening windows/doors – this will not be enough!


  • Intermittent extraction – trickle vents in all rooms accompanied by a fan in a ‘wet’ room (bathroom or kitchen). This is probably what most people have. Its cheap but does not generally result in the best air quality and can be noisy and draughty.



  • Passive stack – a duct system that draws hot, moist air up and out of the home through a central point, these can be expensive to install and their effectiveness depends on air being drawn through the house so may not work in some weather conditions


  • Positive input ventilation – this pumps air in through the loft which escapes through trickle vents and the building fabric. They can be costly to run and may have poor energy efficiency, there may also be issues of forcing warm wet air through the building fabric causing damp and mould to build up.


  • Centralised mechanical extraction – this continually extracts air from “wet rooms” to a central fan and exhaust, the fans in the wet room have a boost function for when they are needed most. These can be complex and expensive to install the duct system and result in cold air being drawn into the house constantly.


  • Decentralised mechanical extraction – this has continuously running extractor fans in wet rooms, with fresh air fed in through trickle vents in non-wet rooms. The fans can be boosted by turning on a light switch, humidity controlled, or a presence sensor. These are simple and cheap but can be noisy and result in draughts from the trickle vents


  • Centralised mechanical ventilation with heat recovery – these constantly extract air from wet rooms and use to to warm the cooler air from outside which is circulated into the non-wet rooms. These are constantly working and boosted in the same way as the system above. These are expensive, complicated and need to be well-designed and maintained. However, they are very energy efficient and do not result in cold draughts.



  • De-centralised mechanical ventilation with heat recovery – these have a heat recovery unit in each room, which can be boosted in the same way as the system above. They are less expensive and simple to install but still require maintenance and are not linked so do not provide an integrated system.


If you are not ready to install a new ventilation system, try these quick wins:

Get a carbon monoxide monitor

Get a simple hygrometer

Use your trickle vents

Make sure the kitchen and bathroom extractor fans are on when they are needed

Clean your extractor fans

Dry your clothes preferably in a well-ventilated wet room if you cannot put them outside

Think about where you dry your clothes, and how this can be better ventilated

Put lids on your pans when cooking


Home Health Check webinar

All graphics are produced by the Carbon Coop.