Further Guidance
Boiler efficiency (%) may be obtained from:
The preferred source of boiler efficiency is the HARP database. If a new boiler is not included in the HARP database, data certified as explained in the links listed above, should be used. If there is no entry in the database and certified data is not available, an indicative gross seasonal efficiency should be taken from Table 4.5.
The HARP database can be found here.
Where it is not clear if the installed boiler is the same as the boiler listed on HARP (for example the full name is not visible on the boiler on site), then a HARP entry can be used if one of the following is available and clearly equates the boiler in the dwelling to a HARP entry1:
A manufacturer’s statement declaring the efficiency of the boiler is not acceptable, it must state it equates to a model that can be found on HARP
For heating system definitions see here. Boiler efficiency may be obtained from:
For twin burner models, the preferred source of boiler gross seasonal efficiency and case heat emission is the HARP database. If a new range cooker boiler is not included in the HARP database, certified data as explained here may be used. If there is no entry in the database or certified data is not available or the model is not of the twin burner type, an indicative gross seasonal efficiency should be taken from Table 4.5.
This guidance applies to independent solid fuel boilers, open fires with a back boiler and room heaters with a boiler.
Boiler efficiency may be obtained from:
The preferred source of boiler efficiency is the HARP database. If a new boiler is not included in the database, certified data should be used if available. Gas and Oil Boiler - Determining gross seasonal efficiency values defines how the gross seasonal efficiency for calculations is determined from test data. If there is no entry in the HARP database and certified data is not available, an indicative gross seasonal efficiency should be taken from Table 4.4.
Solid fuel boiler efficiencies for open fires and closed room heaters with boilers are the sum of the heat to water and heat directly to the room. It is the responsibility of the user/designer/assessor to ensure the ratio of these figures is appropriate to the dwelling. These systems are assigned a lower responsiveness to allow for limitations on the controllability of heat output to the room.
A direct acting electric boiler (also known as an electric flow boiler) heats water for space heating radiators as it circulates. Heat control options are identical to other radiator systems. Water heating is usually by an electric immersion. The cylinder can be within the boiler casing, or it may be a separate cylinder. The treatment in DEAP is the same for both of these cases.
Older warm air heating systems have their own distribution system but in more recent installations warm air systems are frequently combined with a Mechanical Ventilation system with Heat Recovery. For example, a boiler system may feed a heat exchanger at the mechanical ventilation inlet rather than feeding radiators. The heat recovery system data is entered in the ventilation tab in DEAP in the usual way. This caters for the ventilation aspect and the power consumption of the heat recovery system fans. It is possible to use non-defaults for the MVHR system as normal.
The boiler data is entered as normal, using the efficiency from HARP, for example.
In this scenario, "Warm Air Heating Or Fan Coil Radiators Present" is not selected in the ‘Space Heating > Pumps And Fans’ tab, because the warm air heating fan power is entered through the heat recovery system in the DEAP ventilation tab. As per table 4.9 note (d) the warm air heating fan power usage is that of the MVHR in this case.
The responsiveness category is 1 in this system type. It should be assumed that a central heating pump is required to pump water from the boiler to the MVHR heat exchanger unless you can demonstrate otherwise.
The tables of Heating Defaults can be found here