"In the case of improved ratings for EPCs in Scotland certain scenarios can experience an unexpected increase in heating requirement. This is likely to be caused by reduced internal gains from incidental sources caused by inefficiencies in other areas which have now been improved requiring the heating system to compensate. Examples of areas in which this may happen are as follows: Improved lighting: Where lighting has been improved there is likely to be reduced heat generated by the fitting. Where this would have previously conditioned the internal environment to some extent the heating system will now have to compensate. The improvement would be likely to have a net gain. Improved water heating system: Where the water heating system has been improved it is likely to result in reduced thermal losses to the internal environment. This may be due to improved lagging of storage/ secondary circulation or reduced hot water storage. This will have to be compensated for by the heating system however, the net change is likely to be an improvement. Improved glazing: Where windows are improved, it is likely that the improved scenario will benefit from Low-emissivity. This will result in reduced thermal gains which will need to be compensated for in winter months. It is important that the emissivity is considered carefully as the orientation and geometry of the environment will have a great effect on the handling of solar gains e.g. no Low-e in winter will reduce the heating requirement, however in summer months the internal environment may be subjected to high probability of overheating which may need to be compensated for by a cooling system. The inverse is also true.