Portable heat pump: heating for just €62 a year

Heating for €62 a year: the heat pump that promises to break the bill

An air conditioner with a heat pump, bought second-hand for €130, heats a home for six months at eight hours a day for €62 a year. The calculation comes from a user who boasts about having home batteries and paying €0.066 per kilowatt hour around the clock. Far from settling the debate, the figure has peine up a new front around an awkward question: does a heat pump actually work when the thermometer drops below five degrees?

The answer, and here's the twist, depends on where the compressor sits. This user's argument is that units with an outdoor compressor — conventional splits — lose efficiency in extreme cold, while portable units, with the compressor indoors, draw heat from the indoor air and expel the cold air outside. The result, he claims, is performance that doesn't depend on the outdoor temperature. The proof: with 17 degrees outside, the air comes out at 55 degrees; with 7 degrees, the same.

The hole in the window and the €200 pane of glass

The first obstacle isn't thermodynamic, it's structural. To run the hot air duct outside, you have to drill through a window or a wall. Anyone with triple glazing filled with argon dismisses the idea outright: they're not going to punch a hole in an expensive window to test an experiment. The alternative, a custom-drilled pane of glass, cost over €200 back in the day. In practice, the setup demands an installation toll that eats up a good chunk of the savings.

The second sticking point is comfort. Heating systems that blow air force you to raise the temperature to feel the same warmth; heat gathers near the ceiling while your feet stay cold. According to another participant's experience, a 2008 unit already struggles below seven or eight degrees. The proposed solution is to use it as a complement to another heat source, not as a replacement.

How much does it cost to heat an apartment with a heat pump?

The original calculation relies on an electricity price not everyone can get. With batteries, the kilowatt hour comes to €0.066. Without them, the picture changes: with a flat rate of €0.12 per kilowatt hour all day, the annual bill would climb above €130. That's still low compared with the €1,400 estimated for four months of conventional heating, or the two euros an hour it cost a landlord to heat each apartment in his rural guesthouse.

The contrast with the traditional boiler is the underlying argument: while some insist the heat pump is the most efficient option and that anyone still on gas is throwing money away, others point out that there are millions of engineers hunting for the optimal solution and that a €130 gadget from Wallapop isn't going to rewrite thermodynamics. The reasonable doubt lingers: with zero degrees in Madrid, does the air come out at 55 degrees, or does it remain an autumn promise?

The answer will come with winter. Until then, the most striking detail is a different one: the same unit was bought to survive the 50-degree summer. Heating was plan B.