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Humidity

EPA recommends keeping indoor humidity below 60%, ideally between 30 and 50%, to prevent mould. … and 3 more sourced claims.

Explanatory diagramMeasure humidity and investigate sources
Measure humidity and investigate sources
  1. A hygrometer tracks room humidity.
  2. Drying laundry, cooking and other activities add moisture.
  3. Leaks and damp surfaces require separate inspection.
strong evidenceEPA recommends keeping indoor humidity below 60%, ideally between 30 and 50%, to prevent mould.

EPA's home guide says: 'keep indoor humidity below 60 percent (ideally between 30 and 50 percent)'. Above 60%, cold surfaces (wall corners, windows, the unit's fins) reach surface humidity above 80% and mould grows. In Bucharest summers, outdoor humidity can exceed 70% after storms, and the air conditioner is the home's main dehumidifier. See current rates on the Prices page.

Sources (1)
moderate evidenceThe relative humidity range with the fewest adverse health effects is roughly 40–60%.

The classic Arundel, Sterling et al. review (Environmental Health Perspectives, 1986) analysed the indirect effects of humidity – bacterial and viral survival, fungal and mite growth, respiratory infections, chemical emissions – and concluded that overall the 40–60% range minimises these effects (the 'Sterling chart'). Below 30% mucous membranes dry out; above 60% mould and mites increase. Air conditioning set reasonably (24–26 °C) usually brings humidity into this range; very cold settings over-dry the air, and dirty units with reduced airflow dehumidify less.

Sources (1)
strong evidenceEPA requires condensate pans to be clean and drain lines unobstructed; standing water must be fixed immediately.

EPA's mould guide includes 'keep air conditioning drip pans clean and the drain lines unobstructed', and the HVAC guidance requires immediate remediation of standing water and debris. WHO notes that poor condensate drainage leads to overflowing and leaking pans. In splits, the pan and condensate hose clog with biological sludge (biofilm + dust), water stagnates, odour appears and then water drips down the wall. Sun et al. (2024) measured the highest bacterial load of the unit in the pan. Washing the pan and flushing the hose are part of sanitising.

Sources (4)
moderate evidenceDaikin Romania and INSP recommend setting the unit at 25–27 °C and a maximum 6–10 °C difference from outdoors, for comfort, health and lower consumption.

Daikin Romania advises not setting below 25 °C and keeping indoor temperature no more than 6 °C below outdoor (max 10 °C on extreme days) to avoid thermal shock, citing SR EN 15251's 22–26 °C as the optimal summer range. INSP, in its heatwave advice, suggests setting the air conditioner to 27 °C and using a fan for comfort and energy saving. Very cold settings dry the air and mucous membranes, raise consumption and keep the evaporator wet longer – hence dirtier. A clean unit cools efficiently even at 25–26 °C.

Sources (3)

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