- THE MATHSY BIT -
The formula for calculating the volume of hot water required to heat a room is Q = M x C x (dT)
where Q is the heat load of the room (in Kw), M is the mass/volume of the water,
C is the specific heat capacity of water (4.2) and dT is the difference between the
room temperature and the average water temperature of the heating system
(and thus the radiators).
If a room has a heat load of 1kw (1,000w), a desired room temperature of 20°C,
and the water temperature is 70°C for a boiler and 45°C for a heat pump you
can soon see that the dT is halved (70°-20° = 50°, and 45° – 25° = 25°).
Therefore, it is easy to see that the Mass/Volume of the water must double to
achieve the same output of 1kw.