Air conditioning without outdoor unit in Luxembourg: solutions, costs and limits 2026
In Luxembourg, air conditioning solutions without outdoor units offer an efficient alternative for apartment buildings, small spaces, and rental properties. Discover the different types available: monobloc wall units, portable air conditioners and ductable systems. Compare technologies, installation costs and applicable regulations.
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Types of air conditioning without outdoor unit
There are three main categories of air conditioning systems that do not require a visible or significant external unit.
1. Monobloc wall unit (all-in-one)
The monobloc wall unit combines the evaporator and condenser in a single casing fixed to the interior wall. Unlike traditional split systems, there is only a simple air exhaust duct that passes through the façade.
Even the latest generation monobloc wall units require drilling the façade for hot air exhaust. This is not a « work-free » solution for restrictive apartment buildings.
2. Monosplit ceiling system (false ceiling)
This system installs the evaporator in the attic or false ceiling, connected by ducts. More discreet than a monobloc wall unit, it still requires the same facade drilling for the condenser.
3. Portable air conditioner on wheels
Mobile model without permanent installation. Useful temporarily or for rentals, but high energy consumption and poor performance on areas > 30 m².
For apartment buildings prohibiting all work, only the portable remains viable. Otherwise, prioritize monobloc wall unit or monosplit ceiling system depending on available space.
Monobloc wall unit: advantages and limitations
A monobloc wall air conditioning unit operates entirely indoors. The condenser exhausts hot air through a simple Ø 100–150 mm duct. Cooling capacity ranges from 7 to 18 kW.
- Quick installation (1 to 2 days)
- No condensing unit visible on façade
- Easy to maintain and clean
- Moderate installation cost (€1,500 to €3,500)
- Minimal drilling (simple duct)
- Mandatory façade drilling
- Engine noise more audible than split (45–55 dB)
- Reduced performance in high heat (> 35°C)
- Interior condensation in high humidity
- Ineffective on areas > 50 m² without multi-zone
A 12 kW monobloc consumes 2 to 3 kWh per hour. Over 25 summer days (8 hours/day):
Monosplit ceiling system
The monosplit ceiling system installs the evaporator in the attic or false ceiling with air distribution via ducts.
- Clean interior design (invisible unit)
- Low noise from evaporator (< 25 dB)
- High performance on 40 to 80 m²
- Better COP than monobloc (3.2 to 3.8)
- Homogeneous air distribution via insulated ducts
The monosplit ceiling system is the most expensive installation option (€4,000 to €6,500) but offers superior acoustic and aesthetic comfort. It requires available attic or false ceiling space and co-ownership approval for the condenser unit on the facade.
Portable air conditioner
The unit draws indoor air, cools it through a heat exchanger and hot air escapes through a simple Ø 80 mm duct to a window or wall.
- Significant heat loss (hot air in same room)
- Very high energy consumption (COP 1.5 to 2.2)
- High noise (55–70 dB) due to internal compression
- Poor performance on areas > 25 m²
Reserve portable air conditioner for: temporary use < 3 months, rooms < 20 m², rentals prohibiting work.
Solutions without facade drilling: myth or reality?
| Solution | Drilling required | Work duration | Total cost |
|---|---|---|---|
| Monobloc wall unit | Ø 100–150 mm | 1–2 days | €1,500–3,500 |
| Monosplit ceiling | 32 mm tube + ducts | 4–6 days | €4,000–6,500 |
| Portable AC | Ø 80 mm (window) | 0 (window clip) | €500–1,200 |
Air conditioning in apartment buildings: Luxembourg regulations
In Luxembourg, apartment buildings are governed by the Law of May 16, 1979 as amended. The façade is common property — any drilling must be approved by the building manager. Contact building manager before any quote, as some managers systematically refuse all drilling.
Prices and costs in Luxembourg
| Solution | Equipment only | Labor | Total cost |
|---|---|---|---|
| Portable air conditioner | €500 – 1,200 | €0 – 200 | €500 – 1,400 |
| Monobloc wall unit | €1,200 – 2,500 | €800 – 1,500 | €2,000 – 4,000 |
| Monosplit ceiling | €2,000 – 3,500 | €1,500 – 2,500 | €3,500 – 6,000 |
Comparison of solutions
| Criterion | Monobloc wall | Monosplit ceiling | Portable |
|---|---|---|---|
| Energy efficiency (COP) | 2.8–3.2 | 3.2–3.8 | 1.5–2.2 |
| Noise level | 45–55 dB | < 25 dB | 55–70 dB |
| Optimal area | 15–50 m² | 40–80 m² | < 20 m² |
| Lifespan | 8–12 years | 10–15 years | 4–6 years |
Step-by-step installation guide
Wall preparation
Choose a well-ventilated wall, sheltered from direct sunlight. Locate plumbing and electrical wiring before drilling. Mark position precisely (typically 2 m height).
Drilling and refrigerant line routing
Drill two holes for refrigerant lines (Ø 6–8 mm). Use a hole saw for clean passage. Lines must remain thermally insulated. Typical max length: 5–10 m.
Mounting the indoor unit
Install the wall bracket. Check horizontal/vertical level. Unit must be at least 15 cm from ceiling and 30 cm from obstacles for air circulation.
Connecting refrigerant lines
Connect refrigerant lines (color-coded: red high-pressure, blue low-pressure). Wrap with foam insulation. Seal wall passages with caulk or expanding foam.
Electrical connection and testing
Connect to 230V/16A minimum outlet. Test all three modes. Check for leaks, unusual noises, or odors. Enable energy-saving mode if available.
Performance and limitations
No air conditioning without outdoor unit offers the performance of a traditional split system. Above 35°C, efficiency drops 20–30%. COP is 70–80% of a classic split. Summer consumption is up to 50% higher than a split for the same area.
Frequently Asked Questions
Can I install air conditioning without outdoor unit in an apartment building?
Yes, provided you obtain approval from the building manager. Some buildings prohibit all facade drilling; in that case, only a portable AC unit remains viable.
Is a monobloc cheaper than a portable air conditioner?
No upfront. A monobloc costs €2,000–4,000 (equipment + installation), versus €500–1,400 for portable. However, the monobloc uses less energy (lower operating costs).
Is there a true « no drilling » solution?
No. Any effective cooling system (> 5 kW) must exhaust hot air. Only portable AC can be installed via a window (80 mm). Monobloc and monosplit require facade drilling.
Why don’t outdoor-unit-free AC systems heat well in winter?
All thermodynamics concentrates in one indoor unit. When outside temps drop below 5°C, a backup electric resistance activates, negating all energy savings.
What is the COP of a monobloc?
Between 2.8 and 3.2. Better than portable (1.5–2.2) but lower than traditional split (3.5–4.5).
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