AC: Managing 10 to 50 Rented Homes

"We manage 34 units in the Paris region for three family-owned property companies: 12 in Montrouge, 9 in Vincennes, the rest scattered between Massy, Rueil and Saint-Maur. Twenty-two flats have reversible air conditioning, installed between 2009 and 2024 by six different contractors. I have no drawings, no list of models, and I only find out what the units are when a tenant calls. This summer I got eleven calls in three weeks and paid for three call-outs that turned out to be clogged filters."

That is the kind of call we get from lettings managers, property-company directors and private landlords who have crossed a tipping point without noticing. Once you have around ten units, air conditioning stops being a piece of equipment and becomes a technical estate. And a technical estate cannot be managed by waiting for the tenant to call: it is managed through an inventory, a calendar and a contract.

This article is not another reminder of how responsibilities are split between tenant and landlord — that one already exists on this blog. It is an operating manual for managers: how to take back control of a mixed fleet of reversible air conditioners, what it really costs in 2026, and how to phase replacements over several financial years instead of scrambling in July.

The real problem with a portfolio: diversity, not numbers

A landlord with twenty homes fitted with twenty identical units from the same installer has almost no issue at all: one contract, one parts list, one technician who knows the hardware.

What we actually find in a portfolio built up through successive acquisitions:

• wall-mounted splits of 2.5 to 3.5 kW installed across five different periods;
• three to six brands, often including one or two that have vanished from the French market;
• a mix of R410A (units from before 2018–2020) and R32;
• outdoor units on balconies, in courtyards, on technical terraces, sometimes in landing ducts — with building-association approvals nowhere to be found;
• no documentation whatsoever: no manual, no installation invoice, no commissioning certificate.

Every line on that list turns into euros the day something breaks. Not because the repair itself costs more, but because the diagnosis becomes an investigation. A refrigeration engineer who arrives with no model reference, no idea where the pipework runs and no service history will bill an average of 30 to 45 minutes before even opening a cover.

The three hidden costs of having no inventory

Hidden cost	Cause	2026 ballpark figure
Avoidable call-outs	Filters, remote control, circuit breaker, wrong mode selected	€90 to €150 excl. VAT per visit
Diagnostic surcharge	Unknown unit, no history, unidentified part	+€50 to €120 excl. VAT per job
Rental void or goodwill gesture	Uncomfortable home during a heatwave, rent negotiation	from €0 to several hundred euros

Across the 22-unit portfolio described above, these three items added up to more than €2,000 in a single summer. An annual maintenance contract covering the same portfolio costs less.

Step 1: do the inventory once and for all

This is the one step you cannot half-delegate. It is done as a single campaign, ideally between October and March, outside the peak call period.

For each home, we record:

1. Exact brand and model reference of the indoor unit AND the outdoor unit (from the rating plate, not the remote control);
2. Refrigerant type and charge in kg, as shown on the plate — this is the piece of information that determines the unit's entire future;
3. Year of manufacture (often readable in the serial number);
4. Nominal cooling and heating output;
5. Configuration: single-split, dual-split, number of rooms served;
6. Location of the outdoor unit and how it is mounted;
7. Condensate drainage method: gravity or condensate pump;
8. Condition of the filters and heat exchanger on opening;
9. Photos: rating plates, outdoor unit, visible pipework routing.

A pocket laser measure and a simple digital thermometer and hygrometer are enough to complete the survey with room dimensions and a supply-air reading — data that will prove useful the day resizing becomes necessary. Our technicians also note the temperature difference between return and supply air: below 8 °C in cooling mode, the unit is already struggling.

The result fits in a single spreadsheet, one row per home. That document is your asset: it will follow you from one contractor to the next, and it is worth several thousand euros in savings over ten years.

Field tip: schedule the inventory campaign to coincide with check-in/check-out inspections or annual compliance visits. That way you only pay for one mobilisation.

Step 2: a framework contract, not line-by-line billing

A landlord who calls a different repair firm for every incident pays three times over: the one-off rate, the time spent getting familiar with the equipment, and the lack of priority during peak season.

What a multi-site contract changes

In the Paris region, an annual maintenance contract for a residential split costs around €130 to €190 excl. VAT per unit in 2026, with volume discounts above 10 units. We see reductions of 10 to 25 % on a portfolio clustered geographically, far less when the properties are spread across four départements — travel time is the real cost driver.

The contract must spell out the following, and this is where quotes differ:

• the precise scope of the visit: cleaning of filters and the indoor heat exchanger, check of condensate drainage, pressure and temperature readings, cleaning of the outdoor condenser, electrical checks, test in both cooling and heating mode;
• leak-tightness testing where it applies: this is mandatory for equipment containing at least 5 tonnes of CO₂ equivalent of refrigerant (Articles R. 543-75 et seq. of the French Environment Code, implementing the European F-Gas Regulation). A domestic split with 1 kg of R32 does not reach the threshold; a multi-split or a small ducted system may, particularly with R410A. Have this checked unit by unit rather than assumed across the board;
• the contractual response time in the event of a breakdown, and the hours covered;
• the rates for parts and labour outside the contract, with a ceiling above which your written approval is required;
• reporting: who sends you the service report, in what format, and within what timeframe.

The awkward question: who pays for what

Nothing beats clear wording in the tenancy agreement. In practice, we advise the landlords among our clients to keep the maintenance contract at their own expense and to require annual access, rather than recharging it to the tenant through service charges. The reasons are economic, not legal: you retain control over quality, over traceability and therefore over the asset's service life. The respective obligations are set out in detail in our article on air conditioning in a rented home and in the one covering servicing in an apartment building: who decides and who pays.