Heat rises – Blame physics: hot air rises while cold air sinks. That means your upstairs typically gets hotter than your lower levels, even if your air conditioner's working in overdrive. Your roof's hot, too – Unless you have shady tree cover, your roof absorbs a ton of heat from the sun.

Reverse cycle air conditioning refers to a refrigeration cycle that can provide both heating and cooling solutions. This is done by reversing the refrigeration cycle so that the system can heat in winter and cool in summer. The entire system is efficient, adaptable, and flexible.

If you have an air-conditioner that you use for heating in winter – also known as a reverse-cycle air-conditioner – then you are using a heat pump: The air-conditioner is extracting heat from the cool outside air and bringing it into the house via the heat pump cycle.

Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR) or energy recovery ventilation (ERV), is a ventilation system that recovers energy by operating between two air sources at different temperatures. It is used to reduce the heating and cooling demands of buildings.