Internal gains from appliances, cooking and from the dwelling occupants (metabolic gains) are calculated based on the total floor area. Water heating gains as outlined in the previous section are also calculated.
Heat loss to the cold water network is calculated based on total floor area and subtracted from the above gains. Gains from ventilation system fans are also included. No useful gains are assumed from individual extractor fans. Gains from heating system fans and pumps are accounted for later, in the heating system part of the procedure based on entries in the ‘Space heating: pumps and fans’ tab.
Guidance on re-use of data for lighting can be found here
The electricity used for lighting is calculated based on entries in the ‘Lighting’ tab according to the procedure in the lighting calculation section. The calculation allows two options, one where the lighting is known, and one where the lighting design is not known. The tariff applicable to lighting is the on-peak rate.