Marine Air Conditioning Glossary
Twenty-three terms, each on its own page. Most of these mean something slightly different on a boat than in a house, and the difference is usually the whole point.
Marine Air Conditioning Capacity
- BTU/hBritish thermal units per hour — the unit marine cooling capacity is sold in. 12,000 BTU/h is about 3.5 kW of cooling, sometimes called “one ton”.
Marine Air Conditioning Components
- Air handler / fan coilThe quiet cabin-side box containing the fan and the cold coil. No compressor inside.
- Seawater pumpThe pump that moves cooling water through the condenser. Centrifugal, and it must sit below the waterline.
- StrainerA clear-bowl filter between the seacock and the pump that catches weed, grass and jellyfish.
- CondensateWater pulled out of humid cabin air by the cold coil. It must drain to a sump, never the bilge.
- Through-hullThe skin fitting that lets cooling water into the boat. Bronze or composite, below the heeled waterline.
- SeacockThe valve on the through-hull. The one part of the system that can sink the boat.
- Overboard dischargeThe hull fitting above the waterline where the warmed cooling water leaves. Your health check.
- DuctingThe insulated flexible tube carrying cooled air from the unit to the grilles.
- Return airThe path air takes back to the unit, and the grille it passes through. It should be larger than the supply.
- EvaporatorThe cold coil that cabin air passes over. Where the cooling and the dehumidification actually happen.
- CondenserWhere the refrigerant sheds its heat into the seawater. The marine equivalent of the box outside a house.
Marine Air Conditioning How it works
- Reverse cycleA unit that can run backwards to heat the cabin, taking warmth from the seawater instead of dumping heat into it.
Marine Air Conditioning Legal
- ARCtickThe Australian licence anyone handling refrigerant must hold. Ask your installer to show you theirs.
- AS/NZS 3004.2The Australian standard covering electrical installations on boats. Fixed 240 V work is an electrician’s job.
Marine Air Conditioning Power
- Soft startElectronics that limit compressor start-up current so an inverter or small generator can cope.
- Variable speedA compressor that slows down instead of switching off — quieter, and far kinder to a battery bank.
- Duty cycleThe proportion of time the compressor actually runs once the cabin is at temperature.
- Short cyclingA compressor switching on and off too frequently, usually because the unit is oversized for the space.
Marine Air Conditioning Refrigerants
- R410A and R32The refrigerants in current marine units. R410A is standard; newer designs are moving to R32.
Marine Air Conditioning System types
- Self-containedCompressor, evaporator and fan in one box, ducted to grilles. One unit per zone.
- Split systemCompressor in one place — engine room or lazarette — and an air handler in the cabin, joined by refrigerant lines.
- Chilled waterA chiller cools a loop of fresh water; fan-coil units in each cabin draw from the loop.