On 100 m², sizing an air conditioning system is not just a matter of multiplying the area by a standard ratio. The choice of system, the routing of refrigerant lines, and the level of insulation of the building determine a budget that can vary in a ratio of one to ten.
Refrigeration sizing for 100 m²: the 100 W/m² rule is not enough
We regularly observe quotes based on a fixed ratio of 100 W/m², applied without prior thermal analysis. This ratio is only valid for a properly insulated home, with standard ceiling height and moderate exposure.
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In a poorly insulated house, the required power rises to 120 or even 150 W/m², which is an increase of 30 to 50% compared to the simplified calculation. Specifically, where a RT 2012 compliant house would require about 8 kW of cooling power, a house from the 1980s without external insulation will easily require 12 to 15 kW to maintain adequate comfort during heatwaves.
Oversizing poses as many problems as undersizing. An overly powerful outdoor unit runs short cycles (frequent on/off) which wear out the compressor and increase consumption. Before estimating anything, we recommend a room-by-room thermal assessment, taking into account orientation, glazed surfaces, and air renewal rates.
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To accurately assess the installation cost of air conditioning for 100m2, this sizing step is the only reliable starting point.
Multisplit, ducted or monoblocs: which system to cool 100 m²
The choice of system determines thermal comfort, interior aesthetics, and the renovation budget. For 100 m², three architectures dominate.
Multisplit: the most common compromise
A multisplit combines an outdoor unit with several indoor units (wall consoles, cassettes, or low-profile units). To cover 100 m², four to five indoor units are generally required, depending on the partitioning. Each unit can be controlled independently, allowing temperature adjustments room by room.
The main constraint remains the routing of refrigerant lines. Each indoor unit requires a pair of copper tubes, a power cable, and a condensate drain. In renovations, these routing paths often determine the feasibility of the project.
Ducted: uniform comfort, heavy work
The ducted system distributes air through a network of ducts in the false ceilings. It offers total discretion (only the air outlet grilles are visible) and zone regulation if the system includes motorized dampers.
However, the ducted system requires sufficient technical volume to house the air treatment unit and the duct network. In a single-story house without accessible attics, installation becomes complex and costly. We reserve it for new constructions or major renovations with the creation of false ceilings.
Monoblocs and portable units: a false economy for 100 m²
Monobloc or portable air conditioners are inexpensive to purchase. For 100 m², their efficiency is poor: a single unit only treats one room, the noise level often exceeds 60 dB(A), and the expulsion of hot air through an open window creates a parasitic heat gain that negates part of the cooling. For 100 m², monoblocs are not a viable solution.
Actual budget for cooling 100 m²: detailed items
The displayed price of an outdoor unit and its indoor units represents only a fraction of the budget. Here are the items we systematically include in our estimates:
- The equipment (outdoor unit, indoor units, refrigerant lines, supports, and mounting accessories) forms the basis, with significant variations depending on the brand and energy class
- The installation labor includes wall drilling, routing of lines, vacuuming the circuit, and commissioning with refrigerant leak testing
- Additional work (creating conduits, modifying false ceilings, electrical rewiring with a dedicated line to the panel) can represent a third of the total budget in renovations
- Electrical compliance, often overlooked, requires a dedicated circuit breaker and a 30 mA differential for the outdoor unit
The price difference between an entry-level multisplit and a high-end ducted system can reach a factor of ten. The labor cost varies more according to the complexity of the routing than according to the chosen technology.
Reducing the air conditioning budget for 100 m²: concrete levers
The first lever, and the most underestimated, is insulation. Improving insulation before sizing the air conditioning reduces the necessary power and thus the cost of equipment. Additional insulation in attics or the installation of solar films on south and west-facing windows may be enough to lower the power requirement for the outdoor unit.
Regarding financial aid, the situation has tightened. Reversible air-to-air air conditioners are excluded from MaPrimeRénov’. Only the CEE bonus remains accessible for an air-to-air system, provided that a RGE installer is used. The eco-PTZ can only apply if the project is part of a bundle of work that includes insulation or an air-water heat pump.
Other levers not to be overlooked:
- Compare at least three quotes from RGE installers, ensuring that each quote separately details equipment, labor, and additional work
- Prefer an Inverter system, whose variable speed compressor adjusts its power to the actual thermal load and consumes significantly less than an on/off compressor
- Plan for an annual maintenance contract from the first year: cleaning filters and checking refrigerant levels maintain nominal efficiency and prevent costly breakdowns
The operating budget deserves as much attention as the initial investment. A properly sized and maintained system in a well-insulated house will consume significantly less than an oversized unit operating in a leaky building. For 100 m², this consumption gap can amount to hundreds of euros per air conditioning season.