How does it work?

It feels a bit like magic at first, because an air-to-air unit doesn’t “make” heat the way a radiator or heater does. It moves heat from one place to another.

Here’s the idea in plain language.

The short version:
An air-to-air unit (basically a heat pump) takes heat from the outdoor air and pumps it inside. Even when it’s cold outside, there’s still usable heat in the air.

What’s actually happening step by step
1. Heat is collected from outside

The outdoor unit has a coil filled with a special fluid (refrigerant).
This fluid is very good at absorbing heat, even from cold air.

So when outside air passes over the coil:

The refrigerant soaks up heat

The refrigerant evaporates (turns from liquid to gas)

Yes — even at 0°C or below, the air still contains heat energy.

2. The heat is “compressed”

That warm gas is pushed into a compressor.

Compressing it:

Raises its temperature a lot

Concentrates the heat

Think of it like squeezing air in a bike pump — it gets warm.

3. Heat is released into your room

The hot refrigerant gas flows through the indoor unit.

A fan blows room air across the indoor coil:

Heat transfers from the refrigerant into the room air

Warm air is blown back into the room

As the refrigerant loses heat:

It condenses back into a liquid

4. Repeat forever (well, while it’s on)

The cooled liquid goes back outside and the cycle starts again.

Why it’s so efficient:
A normal electric heater:
1 unit of electricity → ~1 unit of heat

An air-to-air heat pump:
1 unit of electricity → 3–5 units of heat

That’s because electricity is mostly used to move heat, not create it.

Common “wait… how?” questions:
“But how can it get heat from cold air?”
Because temperature isn’t “heat vs no heat.”
It’s just how much heat energy there is — and there’s almost always some.

“Why does the air feel like it’s blowing instead of radiating?”
Because heat is delivered by forced warm air, not a hot surface like a radiator