Energy use

The US Department of Energy states that replacing a dirty, clogged filter with a clean one can lower the air conditioner's energy consumption by 5% to 15% and recommends cleaning filters every 1–2 months in season, more often with pets or heavy dust. A clogged filter cuts airflow, the evaporator gets too cold and may freeze, and the compressor works longer for the same cooling. For a 12,000 BTU split drawing about 1 kW, 10% means tens of kWh per season. It is the cheapest energy saving available to the customer.

Energy Saver (DOE) explains that even with a clean filter the evaporator still collects dirt over time, and the dirt layer insulates the fins and reduces heat absorption; the recommendation is an annual check and cleaning when necessary. For the outdoor unit, DOE asks for removal of leaves and vegetation and about 60 cm of clearance. These recommendations match the annual sanitising service exactly: washing the indoor evaporator and the outdoor condenser in place.

Siegel, Walker and Sherman (LBNL, 2002) modelled dust deposition on residential evaporators and estimated that doubling of pressure drop occurs in about 7.5 years – well below the coil's 15–30 year life. The 5–7% airflow reduction gives capacity and efficiency losses under 5% in well-sized systems, but 'much greater for marginal systems or extreme conditions'. Key parameters are filter efficiency and indoor particle concentration. Practical conclusion: clean filter + coil cleaning bring the unit back to design performance.

ASHRAE project RP-1705 (2019) experimentally studied fouling effects on air-cooled condensers of split systems, and earlier work (Pak, Groll, Braun, 2005) measured on room units how dust on the exchanger raises pressure drop and lowers heat transfer. When the condenser cannot reject heat, discharge pressure rises, the compressor draws more power and capacity falls; on very hot days the unit may no longer hold temperature. Poplar fluff, construction dust and leaves are the usual culprits in Bucharest. Pressure washing the condenser (inside-out) is part of the annual sanitising.

In its duct-cleaning guidance EPA draws a useful distinction: research suggests washing cooling components and fans may improve efficiency and service life, whereas cleaning ducts alone has little evidence. EPA adds that the condensate pan must drain properly and standing water must be fixed immediately. For a ductless split, exactly these components – evaporator, blower, pan – are what sanitising cleans. It is also an argument against offers that merely 'blow out' the unit with compressed air without washing.

LG's support page states that 'if the air filter is clogged with dust, cool air may not blow' and recommends 'clean the filter every 2 weeks to improve cooling efficiency'. Daikin notes that running with dirty filters leads to poor cooling and odour. This is the manufacturers' confirmation of the DOE figures (5–15%). For the customer: remove filters, vacuum or wash in lukewarm water (below 40–50 °C) and dry in shade; never refit them wet.