Improved insulation is the key to reducing energy use for

space heating in homes. It is also pretty clear that a

draughty home is a cold home and so requires a lot of

energy to heat it. On the other hand people have a feeling

that you shouldn’t live in a stuffy home with no movement

of air from outside. So what level of ventilation is best?

Build tight, ventilate right is fine as a maxim for new build but doesn’t help when you are trying to improve an old house. To continue to reduce our household carbon footprint by around 10-20% per year makes it necessary to understand which improvements can yield the greatest reductions. By mid-2009 we were planning to add further wall insulation and to reduce heat loss through draught reduction but had no idea which was most significant.

Estimating heat loss by conduction through walls, windows and roof is relatively straightforward since we can quote U values. The ground flooring is more of an unknown since we didn’t know much about its construction (except that it has original suspended wood floorboards over which oak flooring had been laid).

Apparently the heat loss through draughts (infiltration is the technical word) can often be equal to conduction loss in many older leaky houses so it made sense to try to find out how badly our terraced cottage leaked.

We hired a 30 cm diameter fan, improvised a hardboard seal between it and a window opening (gaps covered with duct tape), borrowed a precision barometer able to sense pressure changes of one in one hundred thousandth of normal air pressure. With this kit, we carried out various sequences of opening, closing and sealing internal doors and possible draught points to see if we could identify variations in air flow.

More information  - a technical description of the measurements, calculations and conclusions

We have subsequently done some work on reducing draughts around the hall area so are planning to repeat the experiment one day to see if we can detect any improvement.


Testing for draughts