our living room has its flat ceiling of 4.5 m, then the dining is cathedral topping at 4.5m as well. Both also have high windows (double glazed). So this is all effectively one room which also includes the kitchen and stair landing and void down to our entry. In total there are 5 floor mounted ducts serving this whole area. It takes about 30 mins to come from 15 to 21 deg using yesterday as the example. I can also program it to come on if needed.