Heating load in Watertown
A home in Watertown has to be heated against a design temperature of −28.4 °C. That figure is measured, not modelled: it is the 1st percentile of daily minimum temperature over 30 years at Watertown Intl Airport, 9 km away.
Design temperature
−28.4 °C
Heating degree days
3,216
Coldest month
Jan
Coldest night on record
−41.7 °C
How many kilowatts
Heating power needed at the design temperature, in kilowatts, for a detached house. Pick the row that matches the building.
| Construction | Detached | Semi-detached | Terraced | Top-floor flat | Mid-floor flat | Ground-floor flat |
|---|---|---|---|---|---|---|
| Uninsulated, single glazed | 31.2 kW | 27.4 kW | 24.3 kW | 26.6 kW | 13.0 kW | 15.9 kW |
| Unfilled cavity, early double glazing | 21.1 kW | 18.2 kW | 15.9 kW | 15.5 kW | 9.4 kW | 11.7 kW |
| Insulated to 1980s standards | 12.1 kW | 10.8 kW | 9.9 kW | 9.3 kW | 6.7 kW | 8.5 kW |
| Modern, roughly 1995-2010 | 7.4 kW | 6.8 kW | 6.2 kW | 6.0 kW | 4.5 kW | 5.5 kW |
| Current building regulations | 5.7 kW | 5.2 kW | 4.8 kW | 4.7 kW | 3.5 kW | 4.3 kW |
| Passive house | 3.3 kW | 3.0 kW | 2.8 kW | 2.7 kW | 1.8 kW | 2.4 kW |
Where the heat goes
For a 120 m2 detached house of this construction, at the design temperature.
| Element | W | Share |
|---|---|---|
| Walls | 3,976 | 33% |
| Roof | 1,162 | 10% |
| Ground floor | 784 | 7% |
| Windows | 2,265 | 19% |
| Thermal bridges | 665 | 6% |
| Ventilation and draughts | 3,209 | 27% |
| Heating load | 12,061 | 12.1 kW |
Calculate it for your own home
The climate half of this is measured. The building half is yours to supply.
Monthly mean temperature
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| °C | −5.9 | −5.0 | −0.2 | 6.7 | 13.4 | 18.3 | 21.2 | 20.3 | 16.2 | 9.9 | 4.0 | −1.9 |
Where these numbers come from
- Measured: the design temperature, the degree days and the monthly means. All of it from one station, Watertown Intl Airport, over 30 complete years.
- Assumed: everything about the building. The U-values are typical published figures for each construction era, not a survey of your house. Two houses of the same age and size can differ by a factor of two.
- No credit is taken for sunshine or for the heat given off by people and appliances. That is the EN 12831 convention, because the design condition is a still, dark night.
- This is space heating only. Domestic hot water is a separate load.
- This is a calculation, not a survey. Before spending money, have the building assessed.