Design Conditions
Design External Air Temperature
The external design temperature is by default based on the closest reference weather location to the postcode of the property. The nearest location is determined by the shortest straight line distance between the geographic centre of the postcode area and the latitude/longitude of the weather station.
The design temperature retrieved is the hourly dry bulb temperature that was equal to or exceeded for 99.6% of hours in a year. This data is derived from CIBSE Guide A - Environment Design (2015) Table 2.5 for 14 UK sites, reproduced for reference in the table below.
| Location | Weather Station | Altitude (m) | 99.6% Dry-bulb Temperature (°C) |
|---|---|---|---|
| Belfast | Aldergrove | 63 | -3.2 |
| Birmingham | Coleshill | 96 | -5.1 |
| Cardiff | St Athan | 49 | -3.1 |
| Edinburgh | Gogarbank | 57 | -5.4 |
| Glasgow | Bishopton | 59 | -5.6 |
| Leeds | Church Fenton | 8 | -3.3 |
| London | Heathrow | 25 | -3.0 |
| Manchester | Woodford | 88 | -4.5 |
| Newcastle | Albermarle | 142 | -3.7 |
| Norwich | Marham | 21 | -4.6 |
| Nottingham | Watnall | 117 | -3.9 |
| Plymouth | Mountbatten | 50 | -1.5 |
| Southampton | Hurn | 10 | -4.8 |
| Swindon | Brize Norton | 82 | -4.6 |
Additionally, for every whole 100m that the property altitude exceeds the reference location altitude, the design temperature will be reduced by 0.6°C.
NOTE
Refer to CIBSE Guide A - Environment Design (2015) Section 2.5 for more information.
Mean Annual External Air Temperature
The annual mean external air temperature is by default selected based on the closest reference weather location to the postcode of the property. The nearest location is determined by the shortest straight line distance between the geographic centre of the postcode area and the latitude/longitude of the weather station.
The temperature retrieved is the mean annual air temperature that was recorded at each location between 1981-2010. This data is derived from MET Office weather records and referenced in the MCS Heat Pump guidance document (MGD 007) as Table B1.
| Region | Weather Station | Annual Mean Temperature (°C) |
|---|---|---|
| Borders | Boulmer | 9.0 |
| East Pennines | Finningley | 10.0 |
| East Scotland | Leuchars | 8.8 |
| East Anglia | Honington | 10.1 |
| Midlands | Elmdon | 9.8 |
| North East England | Leeming | 9.4 |
| North East Scotland | Dyce | 8.5 |
| North West England | Carlisle | 9.4 |
| North West Scotland | Stornoway | 8.6 |
| Northern Ireland | Aldergrove | 9.4 |
| Severn Valley | Filton | 10.6 |
| South East England | Gatwick | 10.2 |
| South West England | Plymouth | 11.0 |
| Southern England | Hurn | 10.4 |
| Thames Valley | Heathrow | 11.3 |
| Wales | Aberpoth | 9.9 |
| West Pennines | Ringway | 10.0 |
| West Scotland | Abbotsinch | 9.1 |
NOTE
Refer to MCS Heat Pump guidance document (MGD 007) for more information.
Heating Degree Days
By default, the heating degree days used to calculate annual energy estimates are based on the postcode area of the property. There are 124 postcode areas covering the whole of the UK as well as the Channel Islands and Isle of Man.
This data is derived from MET Office historical weather records using a base temperature of 15.5°C.
| Postcode Area | Degree Days |
|---|---|
| AB | 2668 |
| AL | 2033 |
| B | 2425 |
| BA | 1835 |
| BB | 2228 |
| BD | 2307 |
| BH | 2224 |
| BL | 2228 |
| BN | 2224 |
| BR | 2255 |
| BS | 1835 |
| BT | 2360 |
| CA | 2388 |
| CB | 2033 |
| CF | 1835 |
| CH | 2228 |
| CM | 2033 |
| CO | 2254 |
| CR | 2224 |
| CT | 2255 |
| CV | 2425 |
| CW | 2228 |
| DA | 2255 |
| DD | 2577 |
| DE | 2228 |
| DG | 2483 |
| DH | 2370 |
| DL | 2388 |
| DN | 2307 |
| DT | 2224 |
| DY | 2425 |
| E | 2033 |
| EC | 2033 |
| EH | 2577 |
| EN | 2255 |
| EX | 1858 |
| FK | 2577 |
| FY | 2388 |
| G | 2494 |
| GL | 2425 |
| GU | 2033 |
| GY | 1800 |
| HA | 2033 |
| HD | 2307 |
| HG | 2307 |
| HP | 2033 |
| HR | 2425 |
| HS | 1800 |
| HU | 2307 |
| HX | 2228 |
| IG | 2033 |
| IM | 2228 |
| IP | 2254 |
| IV | 2668 |
| JE | 1800 |
| KA | 2494 |
| KT | 2033 |
| KW | 2668 |
| KY | 2577 |
| L | 2228 |
| LA | 2388 |
| LD | 2161 |
| LE | 2425 |
| LL | 2228 |
| LN | 2307 |
| LS | 2307 |
| LU | 2033 |
| M | 2228 |
| ME | 2033 |
| MK | 2425 |
| ML | 2494 |
| N | 2033 |
| NE | 2370 |
| NG | 2254 |
| NN | 2425 |
| NP | 2425 |
| NR | 2254 |
| NW | 2033 |
| OL | 2228 |
| OX | 2425 |
| PA | 2494 |
| PE | 2254 |
| PH | 2668 |
| PL | 1858 |
| PO | 2224 |
| PR | 2388 |
| RG | 2033 |
| RH | 2033 |
| RM | 2033 |
| S | 2228 |
| SA | 2161 |
| SE | 2033 |
| SG | 2033 |
| SK | 2228 |
| SL | 2033 |
| SM | 2033 |
| SN | 2425 |
| SO | 2224 |
| SP | 2224 |
| SR | 2370 |
| SS | 2033 |
| ST | 2228 |
| SW | 2033 |
| SY | 2161 |
| TA | 1835 |
| TD | 2483 |
| TF | 2425 |
| TN | 2255 |
| TQ | 1858 |
| TR | 1858 |
| TS | 2370 |
| TW | 2203 |
| UB | 2203 |
| W | 2203 |
| WA | 2228 |
| WC | 2203 |
| WD | 2203 |
| WF | 2307 |
| WN | 2228 |
| WR | 2425 |
| WS | 2425 |
| WV | 2425 |
| YO | 2307 |
| ZE | 2668 |
Design Room Temperatures
The internal room temperatures are by default based on the room type and age band of the property. This data is derived from CIBSE Domestic Heating Design Guide (2021) Table 3.6.
Newer well-insulated buildings will always use a design temperature of 21°C throughout, except for bathrooms which will have a design temperature of 22°C.
| Room Type | Design Temperature (°C) (Age Band A-J) | Design Temperature (°C) (Age Band K onwards) |
|---|---|---|
| Bathroom | 22 | 22 |
| Bedroom | 18 | 21 |
| Bedroom with en-suite | 21 | 21 |
| Bedroom/study | 21 | 21 |
| Breakfast room | 21 | 21 |
| Cloakroom/WC | 18 | 21 |
| Dining room | 21 | 21 |
| Dressing room | 18 | 21 |
| Family/breakfast room | 21 | 21 |
| Games room | 21 | 21 |
| Hall | 18 | 21 |
| Internal room/corridor | 18 | 21 |
| Kitchen | 18 | 21 |
| Landing | 18 | 21 |
| Lounge/sitting room | 21 | 21 |
| Living room | 21 | 21 |
| Shower room | 22 | 22 |
| Store room | 18 | 21 |
| Study | 21 | 21 |
| Toilet | 18 | 21 |
| Utility room | 18 | 21 |
NOTE
Refer to CIBSE Domestic Heating Design Guide (2021) Section 3.5.3.2 for more information.