If the problem is high humidity or condensation, the first step is to reduce the amount of water vapour in the air:

Table 9-1 shows the maximum levels of indoor relative humidity at 20ºC (68ºF) at which there will be no condensation on conventional double-glazed or energy-efficient windows at various outside temperatures.

It can be difficult to accurately measure and maintain the recommended humidity levels. One simple approach is to let your windows become your indicator. If excessive condensation appears on the interior surface of double-glazed windows (except those in the kitchen and bathroom), you have too much moisture in the air. Alternatively, you can also use a hygrometer to monitor humidity levels.

Occasional condensation does not pose a problem. Excessive condensation or frosting is an indication that you should reduce moisture production or increase ventilation. Refer to the Health and safety considerations for energy-efficient renovations of our website.

Finally, if you are replacing your space heating and DWH systems with high-efficiency sealed combustion equipment, this may affect indoor air quality. Combustion air from outside directly connected to equipment helps reduce spillage and uncontrolled combustion air from entering the home. However, using outdoor air as part of the combustion process reduces air changes in the home and may cause humidity levels to rise.

Table 9-1 Maximum indoor relative humidity levels