Hi,
If anybody is considering using hot and cold aircon units for heating, I would suggest that they buy the Inverter type units.
A normal unit will use approximately 30% more electricity. This is because when a motor starts up it takes up to 6 times the normal running current to get it started, albiet only for seconds, however this happens everytime the motor starts. When the room reaches the set temperature the motor cuts off. Then when the set temperature calls for heat or cold, the motor starts up again.
An inverter unit is more economical due to the fact that when the set temperature is reached, instead of shutting down, the motor continues to run but at a slower speed. This allows the temperature to remain constant in the room much easier.
Inverters however do cost a bit more than a normal hot and cold unit.
Also a thing that intrigued me about aircon units that heat also, I originally thought that the units actually had a heating element in them to make the heat. Not so, the cooling works the same as any fridge or freezer where the gas is compressed to a high pressure then released through a valve sort of going from a small bore pipe into a larger bore pipe. This allows the gas to expand and give the cooling effect. It is know as the Jules thomson effect.
For heating, the opposite takes place with the gas going from a low pressure into a higher pressure thus giving the heating effect.
Hope this helps. Ian