Cooling 40 m² takes more than a BTU rating

Real models and CHF price references

Individual observations from the Swiss market, not a market average or Freath selling prices. These are not offers. Availability, accessories and delivery need checking again at purchase.

Selected by configuration and advertised maximum area. No in-house measurements or guarantee for your room. The PortaSplit’s differing 40/42 m² figures and the PAC 3810 S’s older delivery message remain points to check. Freath does not currently sell these models.

Understand the space

An L-shaped room, partitions or an open kitchen can limit air distribution across 40 m². Sketch the connected space instead of simply adding together the areas of separate rooms.

Match the setup to your use

Claims such as “up to 40 m²” depend on conditions. Ask what those conditions are. Extensive glazing or a top-floor location may call for a more detailed cooling-load assessment.

A transparent starting estimate

At 40 m² with a 2.5 m ceiling, our central assumption of 40 W/m³ gives 4.0 kW of cooling, about 13,648 BTU/h before the sunlight adjustment. This is an educational scenario, not a product recommendation. Adjust the assumptions in the calculator.

Check before buying

Window type and compatible kit; hose route; footprint and clearances; capacity and test method; noise at the setting you will use; electrical input. Even a well-sized unit depends on an appropriate installation.

Compare assumptions, not just floor area

The table keeps ceiling height at 2.5 m and sunlight factor at 1, varying only the thermal assumption between 30, 40 and 50 W/m³. These are not certified building categories. They show why one floor-area number cannot reliably select a capacity or a particular model.

Observe how the room changes during the day

Record when sunlight reaches the room, what shading is available and which equipment is running. An open door to a kitchen or corridor changes the space actually being treated. Compare your most demanding use with an ordinary day. If they differ substantially, an average may conceal discomfort at the time that matters most.

Turn an estimate into a product decision

Next, check the manufacturer’s capacity and test conditions, then consider noise, window setup and electrical input. Do not pick a unit simply because the BTU number in its name exceeds the estimate. A nominal rating and a calculation scenario do not together guarantee an achieved room temperature.

Translate floor area into the volume you will cool

A 40 m² room with a 2.5 m ceiling contains 100 m³. Raise the ceiling to 3 m and the volume becomes 120 m³, even though the floor area stays the same. Measure the actual height and note any open staircase or gallery connected to the room. For a sloping ceiling, use a reasonable average height rather than only its highest point. Volume does not capture the entire heat load, but it exposes a useful assumption. It prevents you from comparing your space with an advertised coverage figure based on an unknown ceiling height or a completely different room layout.

Use three scenarios rather than one precise-looking answer

For 100 m³, our educational assumptions of 30, 40 and 50 W per cubic metre give 3.00, 4.00 and 5.00 kW of cooling before the sunlight adjustment. These figures are not a sizing standard or certified minimum capacities. They show how sensitive the estimate is to the assumptions. Use the middle scenario as a starting point and write down what makes your room different: roof exposure, external blinds, large windows or equipment producing heat. Selecting the lowest figure simply to fit a cheap unit into the result is not a sound decision. Unusual conditions require a closer assessment of the building.

Separate purchase cost from the cost of running the unit

A price for an air conditioner serving 40 m² may exclude suitable window accessories. Make separate budget lines for the appliance, compatible installation parts and electricity. As an example, an average electrical draw of 1 kW over six hours uses 6 kWh. At an assumed CHF 0.30/kWh, that costs CHF 1.80 per day, or CHF 36 across twenty identical days. This is not measured consumption for any model in the table, and the tariff is not a Swiss universal rate. Use your own electricity price. Equal cooling capacities do not necessarily mean equal operating costs in your particular installation.

Rehearse the installation before placing an order

Mark the appliance footprint on the floor and add the clearances specified in its manual. Check whether the door can still open and whether you can reach the bed, desk and storage without stepping over a hose. Then plan the heat outlet. Wheels make a monoblock movable but do not remove the need for a sensible exhaust route. The sealing kit must fit the actual window dimensions and opening mechanism; a universal label alone does not establish compatibility. For a portable split, check the route of the connecting line and a secure outdoor-unit position instead. Resolve these points before purchasing.

Make a home trial answer a specific question

If the return terms allow a trial, decide beforehand what you want to observe. Record temperature at the same point away from the cold air jet, along with time, weather, shading and target temperature. Listen from your normal seat or sleeping position and check how easily you can reach the filter. Fast cooling immediately beside the outlet does not describe comfort across the room. Your observations will not be equivalent to a standardised laboratory test, but they can expose awkward placement, intrusive noise or controls that do not suit your routine. Judge the appliance against the use you actually planned.

Keep unknown specifications visibly unknown

A missing specification is not an advantage. A page with no electrical-input figure does not establish low consumption, and an omitted noise figure does not establish quiet operation. Ask for the exact variant, the operating mode behind a measurement and a complete accessories list. Freath model pages separate documented information from questions that still need checking before purchase. Market price references are dated observations. They are neither Freath selling prices nor promises that a unit will be available at that amount when you order. A familiar brand name also cannot replace checking the documentation for the exact model you are considering.

Deal with an L-shaped 40 m² living room

In an L-shaped layout, air may not reach the section beyond the corner as readily as the area in front of the appliance. Draw tall furniture and openings on the plan and mark where you spend most of your time. Temperature beside the outlet is not a reliable measure of the distant section. If you need both zones to remain similar, assessing air distribution matters more than selecting a higher BTU figure alone. Bring the layout and intended operating hours to a consultation. This makes it possible to discuss whether a single appliance position can reasonably serve the task you have in mind.

Read PortaSplit and PAC 3810 S figures carefully

The documented commercial source describes the PortaSplit at around 40 to 42 m², while the PAC 3810 S is listed for up to 50 m². Turning that difference into a performance ranking would be misleading. It does not establish which unit cools your lounge faster or which sounds less intrusive. The internal Freath pages therefore separate configuration, heat exhaust and missing information. Read that assessment alongside the sizing example. Without matching test conditions, this remains a documentation comparison. Freath has not carried out a shared laboratory test and does not claim measured temperature or sound differences between these models.

Account for occasional gatherings

A living room used by one person during the week may host several guests at the weekend. Decide which situation should drive the choice. Light everyday use does not automatically represent an afternoon with guests, cooking and sunlight across a large window. Close shading before the room overheats and consider when cooling will start. These steps cannot turn an undersized appliance into a suitable one, but they make the assumptions clearer. If you expect a stable temperature during the most demanding days, state that requirement explicitly. An advertised 40 m² coverage figure alone cannot answer whether that particular requirement will be met.

Record the room conditions for advice

A useful consultation starts with more than the number forty. Bring window dimensions, ceiling height, the direction the glazing faces and a sketch showing the main seating area. Explain whether cooling is needed for daytime work or evening use. These details help distinguish a distribution issue from a capacity question without treating either as a proven diagnosis.