See linked resources at the bottom for more information on how to use this tool

Location, Dimensions and Occupancy
Altitude m

Name Area Height Volume
{{ }} m2 m {{ floor.volume | toFixed(1) }} m3
Add Floor

Total floor area{{ data.TFA | toFixed(1) }} m2
Total volume{{ data.volume | toFixed(1) }} m3

Floor area based occupancy {{ data.sap_occupancy | toFixed(2) }} people
Use custom occupancy
Custom occupancy people
Element type Category U-value K g⊥ gL ff
{{ key }}
Add Element Type

ID Type Length Height Area U W/K
m m {{ element.netarea | toFixed(1) }} m2 m {{ element.uvalue }} {{ element.wk | toFixed(1) }} W/K
Add Element

Thermal Mass Parameter (TMP)
Use global TMP value (ignore the k value of individual elements)

Thermal Bridging
Total External Area {{ data.fabric.total_external_area | toFixed(2) }} m2
Thermal bridging heat loss factor (y) p76 W/m2.K
Thermal bridging heat loss {{ data.fabric.thermal_bridging_heat_loss | toFixed(2) }} W/K

Total fabric heat loss{{ data.fabric.total_heat_loss_WK | toFixed(2) }} W/K
Ventilation heat loss{{ data.ventilation.average_WK | toFixed(2) }} W/K
Total W/K heat loss{{ data.totalWK | toFixed(2) }} W/K
Total fabric thermal capacity{{ data.fabric.total_thermal_capacity | toFixed(2) }} kJ/K.m3
Annual solar gains{{ data.fabric.annual_solar_gain | toFixed(2) }} W ({{ data.fabric.annual_solar_gain_kwh | toFixed(2) }} kWh)
Ventilation Type
Dwelling construction
Suspended wooden floor
Draught lobby
Percentage draught proofed %
Number of sides sheltered sides
Use air permeability test result
Air permeability value
System air change rate AC/h
Balanced heat recovery efficiency %
System specific fan power W/m3

Intentional vents and flues
Name Ventilation rate (p10, section 2)
Add ventilation point

Extract ventilation points
Name Ventilation rate (p10, section 2)
Add ventilation point
Space heating
Target temperature C
Living area m2
Heating hours off weekday
Heating hours off weekend
Heating off during summer
Use utilisation factor for gains
Enter custom monthly internal temperature values:
Enter custom monthly external temperature values:

Monthly temperatures
Living area {{ item | toFixed(1) }} °C {{ data.annual_m_i_t_living_area | toFixed(1) }} °C
Whole house {{ item | toFixed(1) }} °C {{ data.annual_internal_temperature | toFixed(1) }} °C
Whole house {{ data.annual_internal_temperature | toFixed(1) }} °C
Outside {{ item | toFixed(1) }} °C {{ data.annual_external_temperature | toFixed(1) }} °C
Outside {{ data.annual_external_temperature | toFixed(1) }} °C
Heat demand {{ item | toFixed(0) }} kWh {{ data.space_heating.annual_heating_demand | toFixed(0) }} kWh

Space heating energy requirement: {{ data.space_heating.annual_heating_demand | toFixed(0) }} kWh

Water Heating
Override annual energy content
Annual energy content kWh {{ data.water_heating.annual_energy_content | toFixed(1) }} kWh
Low water use design

Hot water storage
Storage volume L
Hot water control type
Pipework insulation
Storage loss factor known
Manufacturer loss factor (kWh/day) kWh/d
Temperature factor A (Table 2b, p139)
Loss factor (kWh/litre/day, Table 2, p138)
Volume factor (Table 2a, p138)
Temperature factor (Table 2b, p139)
Contains dedicated solar storage or WWHRSs
Solar water heating
Hot water store in dwelling
Community heating

Hot water energy requirement: {{ data.water_heating.annual_waterheating_demand | toFixed(0) }} kWh

Heating Systems
Heating system {{ index+1 }}
Efficiency, fraction & fuel
Fraction of space heat provided (0-1)
Fraction of water heat provided (0-1)
Summer/water efficiency %
Winter/space efficiency %
Temperature and Controls
Main space heating system
(0: low, 1: high, SAP:Table 4d)
Controls (1, 2 or 3, see: SAP:Table 4e)
Temperature Adjustment (SAP:Table 4e) C
Instantaneous water heating
Warm air system

Other energy requirements & losses
Central heating pump
(If not already included in efficiency)
Central heating pump inside
Warm air system specific fan power W(litre/sec)
Fans and supply pumps
(If not already included in efficiency)
Combi loss
Primary circuit loss
Add Heating System
Lighting, Appliances & Cooking
Calculation type:

The total number of fixed lighting outlets (L)
The number of fixed low energy lighting outlets (LLE)
Reduced internal heat gains for lighting:
Annual energy use: {{ | toFixed(2) }} kWh/year

Lighting Fuel Fraction Fuel input
{{ item.fuel_input | toFixed(2) }} kWh/year

Energy efficient appliances and reduced internal heat gains:
Annual energy use: {{ data.energy_requirements.appliances.quantity | toFixed(2) }} kWh/year

Appliances Fuel Fraction Fuel input
{{ item.fuel_input | toFixed(2) }} kWh/year

Reduced internal heat gains for cooking:
Annual energy use: {{ | toFixed(2) }} kWh/year

Cooking Fuels Fraction Fuel input
{{ item.fuel_input | toFixed(2) }} kWh/year
Category Name Power Hours kWh/d kWh/y Fuel Efficiency
W hrs kWh kWh
Add item
Solar hot water
Aperture area of solar collector, m2
Zero-loss collector efficiency, η0, from test certificate or Table H1
Collector linear heat loss coefficient, a1, from test certificate
Collector 2nd order heat loss coefficient, a2, from test certificate
Collector Orientation
Collector Inclination (degrees i.e 35 degrees)
Annual solar radiation per m2 from U3.3 in Appendix U for the orientation and tilt of the collector {{ data.SHW.annual_solar | toFixed(0) }} kWh
Solar energy available {{ data.SHW.solar_energy_available | toFixed(0) }} kWh
Solar water heating pump

Note: The overall performance of solar water systems depends on how the hot water system is used, e.g. daily draw-off patterns and the use of other water heating devices such as a boiler or an immersion. The procedure described here is not suitable for detailed design in a particular case. It is intended to give a representative value of the solar contribution to domestic water heating over a range of users.

Dedicated solar storage volume, Vs, (litres) L
If combined cylinder, total volume of cylinder (litres) L
Utilised annual solar input {{ data.SHW.Qs | toFixed(0) }} kWh
Onsite Generation
Use Solar PV calculator
kWp installed kW
Inclination degrees

Annual Generation Fraction used on-site Feed in tariff
Generation (£/kWh)
Feed in tariff
Export (£/kWh)
Solar PV {{ data.generation.solar_annual_kwh | toFixed(0) }}
Energy requirements and fuel summary
{{ }}
Supplied by: Fraction Demand: {{ item.quantity | toFixed(2) }} kWh/year Fuel input: {{ data.fuel_requirements[index].quantity | toFixed(2) }} kWh/year
{{ f.fuel }} {{ f.fraction | toFixed(2) }} {{ f.demand | toFixed(2) }} kWh/year {{ f.fuel_input | toFixed(2) }} kWh/year

Fuel summary and costs
Fuel type Fuel quantity CO2 factor
Annual CO2 Primary Energy Factor Primary Energy Unit cost Annual standing charge Annual cost
{{ index }} {{ data.fuel_totals[index].quantity | toFixed(2) }} kWh {{ data.fuel_totals[index].annualco2 | toFixed(2) }} kg {{ data.fuel_totals[index].primaryenergy | toFixed(2) }} kWh p/kWh £/year £{{ data.fuel_totals[index].annualcost | toFixed(2) }}
Add Fuel

Total energy cost:£{{ data.total_cost | toFixed(2) }} ({{ data.SAP.rating | toFixed(1) }})
Total energy income (FIT's):£{{ data.total_income | toFixed(2) }}
Net cost:£{{ data.net_cost | toFixed(2) }}

How to use this tool