How the Heat Function on a Portable Air Conditioner Works

Certain models of portable air conditioner have a heating function as well as cooling. Some window air conditioners use what is called a heat strip, which is basically an electric heater, to heat air in heat mode.   People often ask if portable air conditioners have the same type of thing.  The answer is yes and no, the heat function in all the portable air conditioners currently carried by PortableHomeAir is based on the heat pump, but there are models that use heat strips.

Single hose portable air conditioners that cool air with the heat pump are a bit different from central air conditioners. Indrawn air from the room contains heat energy. The heat pump uses compression and expansion of a coolant to remove the heat from some of the indrawn air and concentrate it into a smaller volume of the indrawn air. The majority of the air is cooled by the loss of heat energy. So the indrawn volume of air is split into a 'hot side' and a 'cold side'. Air in the hot side is blown out the window, and that on the cold side is blown back into the room. During this process, moisture in the air returns to liquid form, or condensates. This is how portable ac's dehumidify. Much of the condensate water is used to cool the unit itself.

In contrast, dual hose portable air conditioners draw in outside air as well as room air.  The second hose is actually an intake hose.  This gives them more air flow to work with and balances the amount of air being drawn into the room from outside with the amount being blown out of the room.  This results in a generally more efficient process.

Now back to the question at hand. The heat function is a reversal of the above process. This is done by reversing the flow of refrigerant, so that what was the 'cold side' is now the 'hot side', and vice-verse. In heat mode then, the air returned to the room is the portion into which the heat energy has been concentrated, and the cooler portion is blown out the window.

Since this is a reversal of the normal function, it is often less efficient than the cooling function, and many units have lower BTU ratings for heating than for cooling. This is why one will often see a statement that the heat mode is generally recommended as supplementation when room temperatures are above 50 degrees, and not as the sole source of warm air in a cold room. That is not always the case though, since some units have been designed to be equally efficient in both modes.  Once again, dual hose tends to be a more efficient setup, because even cold outside air contains heat energy, which a heat pump can "pump" into the room, adding heat energy from a source a single hose unit cannot access..

One can get the BTU ratings of both functions from the model's spec sheet, an important piece of information when evaluating which unit is best for a given application.

I hope this brief non-technical explanation will help give readers a basic understanding of how portable air conditioners with heat actually heat. These are not toys or cheap gadgets but pretty sophisticated pieces of equipment applying old technology in a new way to make a versatile, mobile, effective, and relatively inexpensive room air conditioning option.