We need fresh air in occupied buildings, but it also makes sense if we can control it. Draughts are uncontrolled ventilation and are also the cause of considerable heat loss. This can lead to discomfort, or cold, and to higher than necessary heating bills. The good news is that there is something you can do about it. Ventilation is the controlled entry of fresh air into a building to prevent a build-up of stale, damp air that is it unhealthy to live in.
Draught proofing
Draughts are easy, and cheap, to fix but we tend to learn to live with them. It’s just a matter of blocking up any holes which allow warm air out, and hot air in.
There are all the obvious places to seal – gaps around sash windows and under doors, floor to wall joints, ceiling to wall joints, gaps between floor boards, loft hatches, keyholes and letterboxes, and chimneys – but the real culprits tend to be where pipes and cables are brought through walls or floors, and there is often a gap around the pipe or cable.
Some draughts will be so bad that they are easy to spot. You can find the others by using a thermal heat detector or by walking round the house with a lit candle, and noticing where the flame flickers.
Simple draught prevention can be done through curtains and blinds, carpets, and draught excluders.
Otherwise, there are lots of products in your local DIY store for sealing round windows and doors; good old mastic will do the job at the junction of floor and walls, and even gaps between floor boards. Penetrations through walls for pipes and cables can be sealed with mastic, or expanding polyurethane foam for the larger gaps.
Chimney flues can be bricked up or there is a handy balloon-type thing called a Sempaflu that will do the job. It is important to cap the top as well as the bottom to stop rainwater getting in. Sealing the bottom will still allow rainwater into the top, with consequent damp problems now that the flow of air that used to dry it has been blocked.
For windows and doors you can use foam sealant for gaps, which comes in tape form or as spray foam, or metal or plastic brush strips, as well as installing letterbox plates and keyhole covers and attending to cat flaps.
Secondary glazing film can be used for a double glazing effect but, it will need re stretching from time to time, and can tear.
A note of caution; beware of blocking up air-bricks. Make sure they can still circulate air where it is needed, typically to the ground floor joists, under a suspended timber floor. No air means wet or dry-rot could get established. And make sure you don’t block trickle vents in windows or extractor fans.
For loft hatches, you can install foam sealant.
Cost savings
Draught proofing around your windows and doors could save you up to £20 in energy a year. And draught proofing chimneys could you save you an extra £15 a year.
If you draught proof the whole house you could save up to £60 a year and feel more comfortable at home.
Plus, you might find you’re able to turn your thermostat down a little after installing draught proofing, saving you further money.
Ventilation
Ventilation is talked about in terms of air changes per hour. Traditional buildings may experience as many as 4 air changes per hour (this is why draught proofing is worth doing well). A modern building needs a ventilation rate of about one air change an hour. If it’s super insulated it is likely that mechanical ventilation will be needed (which can be linked to a heat recovery system).
Houses are built to let some air in and out. Bathrooms and kitchens require ventilation where there are high levels of moisture, to avoid damp and condensation, as well as rooms with open fires and flues.
You want to have controlled ventilation rather than uncontrolled ventilation, ie planned gaps where air can escape.
MVHR only works with a high level of air tightness, and must be fitted carefully so that the energy used to drive it is not greater than the heat savings it delivers. The jury is out on whether it is worth retrofitting a system (the ducting is big, bulky and ugly, and you need space in the roof for the air handling unit). However, if you are considering it, it is important to have an air pressure test to find where the leaks are, and then seal them up. The air tightness should be less than 5 cubic meters per hour (that’s twice as good as current building regulations).
How to air a room in winter
If you don’t have good ventilation in a room, it is better to turn off the heating and open the window for a five minute burst of air, than to leave the heating on and the window half open for a long time.
Trickle vents
Modern window frames generally have small vents which you can open and close at will. These can be used when a small amount of fresh air is needed (instead of opening the window).
Extractor fans
These are generally used in bathrooms and kitchens. They can operate automatically when a certain level of humidity is reached, or come on with a light, or be controlled manually.
Mechanical ventilation
In PassivHaus and other super insulated buildings, mechanical ventilation with heat recovery (MVHR) is used to extract warm, humid air from rooms such as the bathroom and kitchen via a heat exchanger. Fresh air is drawn from outside, warmed in the heat exchanger and delivered to cooler room such as the lounge and bedrooms.
MVHR only works with a high level of air tightness, and must be fitted carefully so that the energy used to drive it is not greater than the heat savings it delivers. The jury is out on whether it is worth retrofitting a system (the ducting is large and can be unsightly , and you need space in the roof for the air handling unit). However, if you are considering it, it is important to have an air pressure test to find where the leaks are, and then seal them up. The air tightness should be less than 5 cubic meters per hour (that’s twice as good as current building regulations).
How to air a room in winter
If you don’t have good ventilation in a room, it is better to turn off the heating and open the window for a five minute burst of air, than to leave the heating on and the window half open for a long time.
