In the recent hot weather the house has been plenty cool enough downstairs (between 21°C and 22°C) but it's been getting a bit warm upstairs (typically around 24°C to 25°C in the bedroom).  This is with the MVHR running continuously in cooling mode, as that can only provide about 1.4 kW of cooling capacity, split across all the rooms in the house.   I've been kicking myself since the house was first built that I didn't allow provision for installing a split aircon unit high up in the c