Does Air Conditioning Make the Outdoors Hotter? Why We Need to Get the Science Right

On a recent Radio 4 programme, Becky Taylor, lead of the Overheating Task Group at the Chartered Institution of Building Services Engineers (CIBSE), suggested that using air conditioning “makes the outside temperature hotter.” While the comment was likely aimed to raise awareness about passive cooling and energy use, it risks creating confusion about how modern air conditioning — and indeed heat pumps — actually work.

At Finn Geotherm, we believe it’s crucial to keep the public conversation around climate, comfort, and energy based on sound thermodynamics.

What Air Conditioning (and Heat Pumps) Actually Do

Both air conditioning and heat pumps use the same underlying technology: the vapour compression refrigeration cycle. This system doesn’t generate heat or cold — it moves thermal energy from one place to another.

• In cooling mode (air con), the system removes heat from indoors and releases it outside.
• In heating mode (ASHP), it extracts heat from the outside air — even on cold days — and moves it indoors.

In both cases, the process is highly efficient, and crucially, no new heat is created — only redistributed.

Yes, there is a small amount of waste heat generated from the operation of compressors and fans, but this is marginal, especially when compared to traditional combustion-based systems or internal gains from inefficient buildings.

A Favourite Question We Ask Clients…

We often like to pose the following –

“If an air source heat pump has a COP of 4:1, and you feed it 5kW of electricity, how much heat does it create?”

The instinctive answers are usually:

• “20kW” (5 × 4), or
• “15kW” (20kW output minus 5kW input).

But the correct answer?

Zero. A heat pump doesn’t create heat — it moves it.

That extra warmth in your radiators or underfloor heating is simply borrowed from the outside air. Unlike a gas or oil boiler, which generates heat by combustion, a heat pump transfers energy that already exists.

Why This Matters for Climate Change

If the goal is to reduce global warming — not just carbon emissions but the amount of actual heat introduced into the environment — then heat pumps are a vital part of the solution.

Combustion-based heating (whether gas, oil, or wood) introduces new thermal energy into the world, as well as emissions. Heat pumps, by contrast, simply move existing heat and do so without adding to the planet’s thermal burden.

And because the electricity powering heat pumps is increasingly sourced from renewables, their environmental footprint continues to shrink year by year.

The Bottom Line

So, does using air conditioning “heat the outdoors”? Technically, yes — but only slightly, and only locally. In the grand scheme, the heat expelled by an air conditioning unit is trivial, especially when compared with the heat generated by fossil fuel use or the sun hitting dark surfaces in our cities.

What matters far more is efficiency, emissions, and clean electricity — all areas where heat pumps and modern cooling systems excel.

At Finn Geotherm, we believe in moving heat — not making it. Because that’s how we stay comfortable without making the planet warmer.