Heating With a Portable Split: SCOP 4.0 Explained

Most people shop for a portable split in July and discover the other half of the spec sheet in November: the same box that cooled the bedroom is a heat pump, and in heating mode it turns one kilowatt hour of electricity into four kilowatt hours of warmth. That number has a name, SCOP 4.0, and it is worth understanding before you plug in another electric radiator.

What does SCOP 4.0 actually mean?

SCOP stands for Seasonal Coefficient of Performance. It is measured over a standardised European heating season under EN 14825 and answers one question: how much heat do you get per kilowatt hour of electricity, averaged across the whole season? SCOP 4.0 means 4 kWh of heat for every 1 kWh of electricity. A plug-in radiator delivers exactly 1.

The trick is that a heat pump does not generate heat, it moves it. In heating mode the refrigerant cycle runs in reverse: the outdoor unit extracts heat from cold outside air and the indoor unit releases it into the room. It is the same principle behind the roughly 30'500 heat pumps Switzerland installed in 2025 (FWS), shrunk into a box you can move between rooms.

SCOP, COP, SEER: what is the difference?

COP is a snapshot: efficiency at one fixed operating point, often 7 °C outdoor temperature. SCOP is the season average, including mild days, cold snaps, part-load operation and defrost losses, so it is the honest number for comparing devices. SEER is the cooling twin of SCOP, measured over a standardised cooling season.

On the label, SCOP 4.0 earns an A+ for heating. For cooling, the Midea PortaSplit reaches SEER 6.1 (A++), while our own SplitClima S12 manages SEER 5.6 (A+). In heating mode the two are equals on paper: both SCOP 4.0, both A+.

What does heating with SCOP 4.0 cost in Switzerland?

At the 2026 Swiss median household tariff of 27.7 Rp./kWh (ElCom), one kilowatt hour of heat from a SCOP 4.0 unit costs about 6.9 Rp. A four-hour evening at 2 kW average heat output uses 8 kWh of heat, which is 2 kWh of electricity: about 55 Rp. The same evening with a 2 kW electric radiator costs about CHF 2.20.

Heat delivered	Portable split, SCOP 4.0	Electric radiator
1 kWh	~6.9 Rp.	~27.7 Rp.
One evening (8 kWh)	~CHF 0.55	~CHF 2.22
A month of evenings (240 kWh)	~CHF 16.60	~CHF 66.50

The math scales with your local tariff. The 2026 cantonal medians run from 33.25 Rp./kWh in Basel-Stadt down to 21.88 Rp./kWh in Zug (ElCom), so your own numbers shift by roughly a fifth in either direction. The formula stays simple: heat in kWh divided by 4.0, times your tariff.

How warm will the room actually get?

Warm enough, in most cases, because heating a single room takes less power than people expect. As a rule of thumb, a reasonably insulated Swiss room needs about 50 to 100 W of heat per square metre to hold a comfortable temperature in the shoulder season. A 20 m² office therefore needs 1 to 2 kW, and a 3.5 kW unit covers that with margin to spare.

In practice that margin is what you feel: the unit heats the room up quickly, then throttles down to a low, quiet hum to hold the temperature. Deep winter is different, as the limits section below explains, but for the September to November and March to May window, 3.5 kW is more than a single room usually asks for. The same sizing logic as for cooling applies; the table in our BTU sizing guide works in both directions.

When does a portable split make sense for heating?

It shines wherever central heating does not reach or has not started yet: the cold home office, the hobby room, the shoulder-season cold snap in April when the building's heating is already off. It is a one-room device, not a replacement for your heating system.

Typical cases from our customers and the forums:

• Shoulder seasons. Swiss buildings often switch heating off in spring while single rooms still drop to 17 °C in the evening. A portable split bridges those weeks for centimes per hour.
• The one cold room. Attic offices and rooms above garages are chronically undersupplied. Spot heating beats turning up the whole building.
• Replacing resistive heaters. If you currently run an electric radiator regularly, a SCOP 4.0 unit cuts that heating bill to roughly a quarter.
• Weekend and holiday flats. Fast, targeted heat in one room without firing up a whole system.

Where are the limits?

A portable split is honest technology with honest limits. Know them before you buy:

• Cold weather. Output and efficiency fall as the outdoor temperature drops. SCOP 4.0 is a season average, not a promise at minus 10 °C. In deep winter, expect noticeably less than the rated 3.5 kW.
• Defrost cycles. In cold, damp weather the outdoor coil ices up. The unit pauses heating for a few minutes to defrost itself. Normal, but audible and noticeable.
• The window pass-through. In winter, an unsealed gap around the line costs you heat. Use the foam seal, exactly as described in our window venting guide.
• One room at a time. The PortaSplit's line is 2 m long. The unit heats the room it stands in, nothing else.
• The outdoor unit. It makes noise and it drips condensate, which can freeze on a balcony floor. Neighbours and quiet hours apply in winter too.
• Power. Units in this class run on a normal Swiss T13 socket, which handles about 2'300 W continuous (SEV 1011). No electrician needed, but give it its own circuit rather than sharing a fuse with the tumble dryer.

PortaSplit, PortaSplit Cool or SplitClima S12 for heating?

First, the trap: the Midea PortaSplit Cool has no heating function at all. It is the cooling-only model, and the naming is confusing enough that Notebookcheck ran a "risk of confusion" warning about it. If heating matters to you, it is off the list.

That leaves two: the Midea PortaSplit at CHF 1'190.– and our SplitClima S12 at CHF 799.–. Both deliver 3.5 kW, both are rated SCOP 4.0 (A+) for heating, both run at 39 dB(A) at their quietest. The PortaSplit cools more efficiently (SEER 6.1 vs 5.6), which we say plainly because it is true. But if heating is a big part of your use case, the S12 gives you the same SCOP, WiFi control and the window kit in the box for CHF 391.– less.

Quick answers on heating mode

Can the window pass-through stay in place all winter?

Yes. The flat line stays clamped in the closed window, the foam strip seals the slit, and the window still tilts open on the hinge side if you need to air the room. Check the foam once a month; it compresses over time and a fresh strip costs almost nothing in the accessories section.

Does heating mode dry out the air?

The unit adds no moisture and removes very little in heating mode, but warming air always lowers its relative humidity, so winter rooms feel drier. That is true of every heating system, not just heat pumps.

What about the refrigerant?

The S12 runs on R32, the standard refrigerant in modern split units. The circuit is factory-sealed; you never touch it, and there is nothing to refill or maintain beyond cleaning the filters.

Is a portable split worth it as a heater alone?

No. If you only ever need heat, a cheap radiator plus your building's heating is the simpler answer, upfront cost wins. The case for a portable split is the double season: it earns its price in July, when nothing else cools a rental without drilling, and then quietly quarters your spot-heating costs from October on. One device, two seasons, one window pass-through.

Both heating-capable units are currently sold out, with the next batch expected in spring 2027. Join the free waitlist on the SplitClima S12 page or browse all portable split air conditioners; waitlist members get 48-hour early access before the batch goes public.