Portable vs fixed air conditioning in Lisbon: which to choose?

The salespeople at Worten will always tell you to buy a split. DIY blogs will tell you portables are "inefficient". Tenant forums will tell you to avoid drilling at all costs. Who's right? All three, in different contexts. Here's the honest comparison for Lisbon.

The basics first: how they work

A fixed split has two units: an indoor one (which blows out cold air) and an outdoor one (the compressor, mounted on the façade wall or balcony). They're connected by copper pipes carrying refrigerant gas. The outdoor unit expels all the heat out of the flat.

A portable has everything in a single box, inside the flat. A flexible hose runs out through the window and dumps the hot air outside. It's simpler, but there's a loss of efficiency because some of the heat "stays" in the room.

Cooling efficiency

In ideal conditions, a split is about 30–40% more efficient than an equivalent portable in BTUs. But "ideal conditions" means:

• A well-insulated flat (rare in pre-2000 Lisbon)
• A room closed off with a door
• Double glazing

In old Lisbon flats with single-glazed sash windows, the practical difference shrinks. A 9000 BTU portable can bring a 20 m² room down from 32 °C to 24 °C in about 40 minutes. Enough for most people.

Real electricity consumption

The real numbers for Lisbon (EDP simple tariff, ~€0.18/kWh, 2026):

• Inverter split 9000 BTU: 0.8–1.2 kWh/h → €0.18/hour
• Portable 9000 BTU: 1.0–1.4 kWh/h → €0.23/hour

At 8 h/day for 6 weeks: split = €60, portable = €77. A difference of €17/summer. For most people, that doesn't justify the extra €1,000 of buying and installing a split.

Noise

Splits win easily here. The indoor unit makes 22–30 dB (a whisper). Portables make 50–60 dB because the compressor is in the same space (a fridge in defrost mode).

In practice, in Lisbon:

• For sleeping: a split is clearly better. Portables make themselves heard.
• For a living room/office during the day: portable noise competes with the normal Lisbon traffic noise. Almost unnoticeable.
• Recent premium portable models drop to 48 dB — equivalent to a large fan.

Building and landlord restrictions

Here the portable wins with no competition. In Lisbon:

• Classified buildings (Alfama, Bairro Alto, Baixa): the council forbids exterior units on the main façade. Fines of up to €3,500 for an unauthorised installation.
• Condominiums: many require the outdoor unit to be in a specific spot (interior balcony) and to be silent at night.
• Landlords: the standard tenancy contract forbids drilling exterior walls without written approval.
• Lapa, Estrela, Príncipe Real: areas with a restrictive municipal master plan (PDM).

A portable bypasses all of this. It doesn't touch structures. It vents through the window. When you leave the flat, you take it with you (or return it if it's rented).

Quick decision table

Common mistakes when choosing a portable

1. Buying 5000 BTU for a large room. It won't cope. Calculate ~600 BTU per m² in Lisbon.
2. Not sealing the window well around the hose. You lose 30% of efficiency. Use the sealing kit that comes with the unit.
3. Placing it near a hot window. The sensor reads a higher temperature and the unit overworks.
4. Emptying the water tank at the end of the day. Modern models self-evaporate, so you don't need to.

Our point of view

As a rental company, we're biased. But the truth is simple: we don't sell splits because most people in Lisbon don't need one. They need to cool down for 4–6 weeks a year, without drilling walls, without asking the landlord for permission, without having a piece of equipment sitting idle from October to May. A portable solves it. Rented, even better.

If you're thinking about buying, rent a week first. If you like it and really use it all summer, consider investing in a split. Most people find that a week of portable per summer is enough.