Can anyone please size a heater battery for me? On a supply and extract heat recovery air handling unit. (50% efficient for heat recovery) Outside temperature -2 degrees C Room temp/Return air - 21 degrees C Air voume - 1.3 m3/sec Boiler flow and return - 80-60 degrees C. I have been told i need to use Q=M.Cp.DT. Is this right and how would i do this? I have no idea. I know i need to use the Cp of air, 1.02 and the DT of the on/off coil temperatures. I need some guidance on this please. Fill explination would be appreciated. Thanks.