The choice of fuel type from Table 12.1 should be appropriate for the particular heating system, whether main or secondary. Specifying the main heating fuel is usually straightforward but the following points should be borne in mind.
The choices are mains gas, bulk LPG, and bottled gas. Bottled gas is normally used only with gas room heaters. In dwellings where the main heating system uses mains gas or bulk LPG, any gas-fired secondary system should use the same fuel as the main system.
A single electricity fuel type, specified in Table 12.1, is used for all electricity fuelled heating systems. See Table 10a for proportions of electricity used at the on-peak and off-peak rates. This may be used in conjunction with latest fuel costs available from the SEAI Domestic Fuel Cost Comparison available on the SEAI Website to determine expected dwelling heating system running costs but is not required when producing a BER assessment.
Integrated storage/direct systems comprise:
a) electric storage heaters with reduced storage capacity but incorporating a direct acting radiant heater, designed to provide about 80% of the heat output from storage and about 20% from direct acting;
b) underfloor heating designed to meet about 80% of the heating needs at off-peak times and about 20% at on-peak times. This heating can be controlled by a low (off-peak) tariff control which optimises the timing and extent of the off-peak charge according to outside temperature and the quantity of stored heat. Low tariff control optimises the storage of heat in the floor during the off-peak period and is modelled by a higher system responsiveness.
A secondary system is always to be specified when the main system is electric storage heating or off-peak electric underfloor heating.
Solid fuel appliances can use the following fuels:
Some solid fuel appliances, referred to as ‘multi-fuel’, can use more than one fuel type. The flue ventilation loss (see Section 2) does not apply to room sealed pellet boilers and stoves.
For solid fuel boilers and heaters representing the main heating system, the fuel type should be chosen as follows:
1. If the heating appliance is designed to burn only a wood fuel, in other words its design is such as to prohibit the use of any other fuel type, then the appropriate wood fuel type should be selected. Otherwise, a wood fuel should not be selected. This can be demonstrated by one of the following:
2. If a wood fuel has not been selected then ’Solid Multi-Fuel‘ should be selected.
Independent boilers that provide domestic hot water usually do so throughout the year. With open fire back boilers or closed room heaters with boilers, an alternative system (such as an electric immersion) may be provided for heating water in the summer. DEAP assumes that a fraction of 0.33 of the annual water heating is provided by the supplementary electric water heating. Supplementary electric water heating is specified where the main water heater is incapable of providing water heating without space heating as detailed in Section 5, here.
The fuel chosen based on the above guidance will not always be the same as the fuel specified in accredited test data or the HARP listing for the appliance. The following guidance applies when using test data:
Secondary heating systems are taken from HARP, certified data (following the relevant appendix in DEAP) or Table 4a and the fuel options may in practice be determined by the fuel used for the main heating system. For solid fuel heaters, the fuel type should be selected in the manner described in Section 10.3.3 above for main fuel types.