Cleaning methods

EPA states that 'the use of a biocide, such as chlorine bleach, is not recommended as a routine practice' and that the focus must be on physical removal, because dead mould stays allergenic. For a split this means: first pressure washing with a cleaning solution (removes dust, biofilm and spores), then rinsing, then disinfectant on the clean surface. Order matters: disinfectant applied over dirt is largely neutralised by organic matter. 'Antibacterial' sprays through the grille skip the first two steps.

In its air-system cleaning guidance, EPA notes that research has not demonstrated the effectiveness of biocides applied in systems nor ruled out adverse health effects, advising caution and use only of registered products applied per label after mechanical cleaning. This is the basis for discouraging 5-minute 'spray sanitising': the product sits on dirty surfaces and is then blown into the room. Professionally used disinfectants must be authorised (in Romania, biocidal products approved by the Ministry of Health / National Commission for Biocidal Products), applied to clean surfaces and rinsed or left to act per instructions.

An evaluation in the International Journal of Environmental Research and Public Health (2015) tested several commercial antifungal agents on fungi isolated from indoor environments and found variable efficacy depending on agent, species and contact time. The results support EPA's recommendation: disinfectant is a complementary step, not a stand-alone solution. In a split, a product sprayed through a grille does not reach evenly into the blower channels and between evaporator fins, where the biofilm sits. Only direct contact of the water jet and solution ensures full coverage.

An experimental and numerical study (Science of The Total Environment, 2019) showed that fungal spores deposited on internal surfaces of ventilation systems resuspend into the air under airflow, especially at start-up. This mechanism explains the spore peak measured by Shiraishi (2023) and Hamada (2002) in the first minutes after switching the unit on. Spores killed by UV or spray remain just as easy to resuspend and just as allergenic. Hence the importance of pressure rinsing: water physically carries particles into the collection bag instead of leaving them in place.

LBNL summarises: on continuously irradiated coils and pans, reductions of up to 99% in mould and bacteria are achieved, and the Menzies trial found 20–40% symptom reductions; however, 'studies of the health benefits have inconsistent results' and few exist outside healthcare. Engineering studies (Luongo & Miller, 2016; a 2026 review) show UV-C can maintain coil heat transfer and pressure drop. UV-C works only on surfaces it 'sees' – not inside the blower or a shaded pan – and Methylobacterium resists UV within biofilm. For household splits, UV-C is an optional accessory, not a substitute for sanitising.

In Sun et al. (2024), after professional cleaning the bacterial and fungal load fell significantly on the filter, fins, air outlet and drain pan, and Shiraishi et al. (2023) achieved over 99% fungal reduction with alkaline detergent, brushing and pressure washing. Two independent studies from different countries reach the same conclusion: the mechanical method with water and detergent works. They also give the customer a quality criterion: proper sanitising must include the blower and the pan, not just filters and the evaporator face.

A study of residential units in Japan characterised bacterial community structure on different components, and Sun et al. (2024) found different dominant genera on the air outlet, filter, fins and pan. The Building and Environment (2018) review on HVAC microbial contamination stresses that each component has its own humidity, temperature and deposition conditions. In practice, each zone of a split has its own 'flora', and cleaning that treats only one component leaves the rest intact. The full protocol: filters, casing, evaporator, blower, louvres, pan, condensate hose and outdoor unit.

A study (Environmental Science and Pollution Research, 2018) tested whether bus air-conditioning systems spread allergenic fungi into the driver's space and found measurable transfer of spores from the system into breathed air. Although vehicles are a different context, the mechanism – forced air over a contaminated wet surface, discharged straight at the occupant – is identical to a split mounted above the bed. Evidence that airflow 'delivers' spores justifies positioning sanitising as an exposure-reduction measure, not cosmetics.

CDC clearly states that home air-conditioning units don't use water to cool and aren't a Legionella risk; WHO locates the risk in cooling towers, humidifiers and hot-water systems. Many offers on the market use 'Legionella' as a sales argument for split sanitising, which is misleading and can be challenged by consumers (ANPC sanctions misleading commercial practices). The real, proven arguments are: over 99% fungal reduction by washing (Shiraishi 2023), lower bacterial load (Sun 2024), removal of biofilm odour and energy savings (DOE 5–15%).

Manufacturer manuals (Daikin, Mitsubishi Electric, Panasonic) make proper operation conditional on filter cleaning and periodic specialist maintenance, and Romanian commercial warranty certificates generally require proof of maintenance and forbid unauthorised interventions. ANPC is the authority where consumers can report unjustified warranty refusals or misleading practices. For the customer: keep the receipt/service sheet with the date and operations performed – useful both for warranty and for tracking frequency. In-place sanitising without dismantling does not touch the refrigerant circuit and does not put the warranty in question.

CDC's mould and dampness page summarises the effects: in sensitive people, nasal stuffiness, wheeze, irritated eyes or skin; in allergic or asthmatic people, stronger reactions; in immunocompromised and chronic lung patients, risk of fungal infection. CDC recommends humidity control, fixing leaks, ventilation and cleaning mouldy surfaces. This is the right language for the site's health page: no 'cure' promises, but exposure reduction, with the air conditioner treated as one of the wet surfaces in the home.