The secret to a healthy home…

by Blog

… is good indoor air quality! In this blog Emilia talks about key reasons to create a plan for ventilation at home.

We spend about 90% of our time indoors. Given this, it’s important to consider air quality at home.

While most of us don’t really think about the quality of air in our homes, the Environmental Protection Agency in the USA deems it to be among the top five public health threats!

While ventilation is important for every home, if you are making energy efficiency improvements, planned ventilation becomes an even higher priority. A key strategy for making your home warmer is to seal up draughts, however, if you do this without considering ventilation you’ll be storing up problems.

People often get confused when you suggest they seal up draughts but introduce ventilation. The key difference to keep in mind is that ventilation is controlled while draughts are not. Even a very leaky house with lots of draughts may not have good air quality levels, as clean air is probably not flowing through all parts of the home. Remember: ventilation is vital, draughts are deadly!

Moisture, indoor air quality and health

A key reason to ventilate homes is to manage moisture.

By living in a house we create moisture – cooking, drying clothes and even just breathing. These activities increase the humidity of our homes. Health problems can be caused by the humidity level being too high or too low. In the UK climate, and especially in the North West, we are much more likely to have problems with too much moisture than with too little moisture.

Homes in which the relative humidity is at the optimal level of 40-60%, are more healthy in terms of bacteria, viruses, funghi, allergies, chemicals, ozone production and respiratory infections, as shown in the image below.

Image from 

A damp house will feel colder in the winter, and hotter in the summer, and generally be less pleasant and comfortable to be in.

Excessive moisture also damages the fabric of the house. This includes problems of condensation on wall and window surfaces or hidden inside the fabric of the building structure.

Managing moisture in the home

You might think that letting in damp air from the cold outdoors will increase moisture levels in your home – but actually it is good to ventilate even when the outdoor humidity level is high. This is because when cold damp air from outdoors is brought into the house and heated, the ‘relative humidity’ goes down, and the ‘absolute humidity’ stays the same.

Relative humidity is about how close the air is to the ‘dew point’ – when it can’t contain anymore moisture and water will condense out of it. Absolute humidity is the actual quantity of moisture in the air. Warm air can hold more moisture than cold air before it gets to the dewpoint.

When we breathe and cook and shower, we add more moisture into the air, and so the absolute humidity level goes up. By ventilating, we swap warm air with a high absolute humidity with cold air with a lower absolute humidity. By heating our homes, we ensure that the cold air that comes in reduces in relative humidity, so we stay healthy.

The animation below by the UK Centre for Moisture in Buildings does a great job of explaining these issues:

Moisture guidance for existing homeowners, UKCMB

As well as moisture there are many other sources of indoor pollution including cleaning chemicals, volatile organic compounds (VOCs), smells and odours, dust mites and more. Ventilation should move air through and out the house, diluting these pollutants.

Ventilation strategies

For most homes, opening bathroom windows is not an appropriate ventilation strategy. In winter open windows will cool down your bathroom/home, meaning you will lose heat and create more cold surfaces for moisture to condense on and create mould. Relying on opening bathroom windows also doesn’t ensure clean air is moved through your home, leaving indoor pollutants hanging around in your living spaces.

When considering a ventilation strategy there are many variables and it can get confusing. There are a plethora of ventilation systems and products out there that have many pros and cons. Sales pitches are hard to avoid so it’s important to understand your options and consider your needs. We don’t have time to discuss this in this blog – we’ve listed a few sources of good information at the bottom.

Quick tips for improving air quality

Here are a few things you can do straight away, without investing in any building work

  • Always put lids on pans when cooking.
  • Avoid drying clothes indoors if you can.
  • If you have to dry clothes indoors, do it in a ventilated room (avoid the temptation of drying on radiators around the house).
  • Buy a moisture monitor at a DIY shop or building store – this is called a ‘hygrometer’.
  • Get a carbon monoxide monitor if you have a stove or fireplace.
  • If you have trickle vents – use them!
  • If you have mechanical ventilation, use it! (i.e. switch on bathroom extractor fans when you have a shower, or kitchen extractors when you are cooking)
  • Clean any extractor fans you have, now!
  • Use low VOCs paints and materials.

Where to learn more