Marine Air Conditioning

Marine Air Conditioning adequately sized has great advantages. Air conditioning not only cools the boat, but dehumidifies and if you have reverse cycle you can also provide heat in cooler times. Dry boats are not only more comfortable, the onboard systems like it too, and you will be rewarded with less corrosion.

Mermaid M5 air conditioner

If you do not have the power needed for air conditioning you should see the article about boat shades and ventilation. Even if you have air conditioning putting shade over hatches will help the air conditioner work more efficiently. I have seen an A/C thermostat inside a cabin which was in direct sunlight for a few hours per day. That raised the temperature a lot in that place and hence the A/C ran a lot longer than needed.

Air conditioners range from the very simple to the very complicated. The simplest are plug and play portable units that just need power. More complicated fully installed units require power, a dedicated space, ducting, sea water through hulls and discharges. However, the advent of the self contained AC system has made DIY installation easier.

Marine AC

Marine Air conditioning is different from most land Air conditioning because it uses water cooling rather than air cooling. The abundance of water and lack of space makes this preferable.


  • Refrigerant types 110Volt & 12Volt; produces dry cool air
  • Evaporative types 12Volt; produce cool air like an ocean breeze.

Refrigerant air conditioning uses the principle of evaporating and condensing a refrigerant, just like a refrigeration system. Marine air conditioning uses a closed loop with a high and low pressure side. On the high pressure side, refrigerant gas temperature rises rapidly, due to the compressor, it is then cooled and turned into a liquid by the condenser. The warm liquid passes into the low pressure side and evaporates back into a gas via the evaporator. The evaporator needs energy in the form of heat to do this. The heat in question is the heat in the room you wish to cool, hence the room gets cooler. The compressor and all the parts in this closed loop system uses quite a bit of energy so a good source of power is needed.

Evaporative air conditioners use another method, evaporative cooling, from water or ice. Cool air from the water or ice is blown via a fan, to cool down a small area. 110Volt powered air conditioning is available in these systems.

Refrigerant Air conditioning

Split systems are separate condenser units and fans connected by long runs of tube. The long runs of tube the biggest disadvantage of this system and needing a professional to charge the system with refrigerant. Advantages; quieter as compressor is not in living space, and less room is required

Self-contained units contain the condenser, evaporator and fan in one unit and can be installed in the space you are cooling. The typical self-contained unit needs only a 5/8″ non-insulated raw water supply for cooling the condenser. Advantages: easy for DIY installation. These self contained units are the most popular for recreational boaters. The complete units are only a few inches larger that the evaporators of the split systems and the fan coils of the chiller systems.

Chiller systems commonly found on larger yachts and ships, the chiller unit which is typically placed in the engine room, and fan coils placed throughout the boat where needed. The chiller makes cold water that is constantly pumped in a closed loop throughout the numerous fan coils of the vessel.

Carry on portable unit A portable unit placed over a overhead hatch and powered by shore power. These are like the window units seen in houses. Advantages; no need to take up space below and plug into the shore.

110V Boat Air Conditioners

There are two distinct types of Refrigerant Air Conditioning System for marine use.

  • Direct Expansion Systems
  • Tempered Water or Chiller systems

Direct Expansion systems are available as Self-Contained or Split Systems and are more common on mid-range boats. While the Chillers are designed for larger yachts

Direct Expansion Self Contained

Mermaid M5 air conditioner

Self-Contained refrigerant 110V AC units. These self-contained systems are the most popular for recreational vessels and can run on AC power, shore power or generator. These units range from 5,000 BTU up to 30,000 BTU.

For small boats the M5 5,200 BTU air conditioner from Mermaid packs all the features of a large unit into a small tapered footprint. The taper lets you install the unit under a V berth and with the rotatable blower you can easily attach ducting to circulate air around the cabin.

At 15 inches by 11.5 by 11.5 the M5 is one of the smallest on the market.

This unit will run off the Honda 1001i portable 1,000 watt generator, while in cool mode. Another alternative if you have the batteries is to use an inverter. According to Mermaid a 1,800 watt inverter can handle the unit with 450 amp hours of battery. That is a lot of weight, but you will be cool and it will be quiet.

Chilled water Systems

Cruisair MTD

The Cruisair MTD series is designed for installation flexibility, reliability, maximum performance, and easy accessibility for maintenance. Chiller units are generally housed in the machinery space and pipes run to each of the air handlers.

Cold water is made in the chiller and run through the pipes and through the air handlers. This is a more complicated system to install, but for larger vessels makes sense.

Portable Air Conditioner

portable cruiseair

Living on a small boat for even a weekend in the summer is going to be warm. For small boats a carry on air conditioner that fits over your cabins deck hatch can make life much easier. The unit runs off normal dock marina shore power. The hatch needs to be larger than 12 by 12 inches for the unit to fit.

Types of Refrigerant Air conditioning


12v refrigerant systems; these systems have all the basic parts of the 110Volt systems. The system comprises; self-contained 12V unit, thru hulls and discharges, power, installation and ducting. They come into their own on small boats without the space for a generator.

12 V Evaporative coolers are completely self-contained and do not need any sea water for cooling. These are the simplest systems.

12 Volt DC Air Conditioners

The advantage of 12v DC is that you can use your battery system and not need shore power or a generator, great if you are lying at anchor in a small boat. Many small boats do not possess AC power, plus they have small spaces, perfect for DC air con. Still the problem is draining batteries so monitoring is a must. It would be best to have a battery bank just for the air conditioning separate from starter batteries. 110Volt refrigerant air con requires large start up loads, DC systems do not have this high startup load.

12 V air conditioning is limited to small units, due to the power required.

For a small cuddy cabin of around 200cu ft a 3,000 BTU air conditioner will suffice (200 * 15). Power to this device for 8 hours you will need 3 group 27 batteries (or similar combination) totaling 270-315 amp hours. If you run the engine and have a large alternator you can boost power to the batteries. If you are running the AC and your batteries are getting down to 60% discharge, you can run the engine.

A 12Volt system like the ones below can cost in the $2,300 – $2,900 range, including the unit and pump. You need to add a water inlet and discharge, plus DC power to the inverter.

12Volt Refrigerant Air Conditioner

DC Cuddy; 120v with dc module.

DC cuddy 12 Volt AC

This small A/C 12V powered unit can fit under a v berth. Ideal for small cabin cruiser or sailboat for the occasional stay overnight. This small unit can make small boats comfortable where a traditional AC unit would be too big. 12V power and produces 3,500BTU. The unit is powered by 3- 100 amp AGM batteries and run time is approx. 8 hours between battery charges.A 12Volt system like the ones below can cost in the $2,300 – $2,900 range, including the unit and pump. You need to add a water inlet and discharge, plus DC power to the inverter.

If you have a small powerboat say 20-25 foot with a small interior a DC air conditioner works. The engine is operating when you are away from shore and so the alternator (check the alternator output) is beefing up the batteries, so for a night at anchor the DC air con can do its work. Check your battery bank for the required capacity.

MightyKool M400 Evaporative Coolers

MightyKool M400 Evaporative Coolers

An evaporative cooler (wet air cooler) is a device that cools air through the simple evaporation of water. Evaporative coolers are simple much cheaper and do not need thru hulls or any complicated installation.

MightKool M400 is a Self-Contained, Cooling System integrated into the lid of an Igloo ice chest. You can add enough ice to the ice container of the M400 to have air conditioning up to five hours. If you are using water the M400 will operate much longer. The two vents can be moved to direct cool air in different directions and there is hosing you can also add to give it more reach.

MightyKool will not cool an entire room, but is designed to be a personal cooler, making the immediate surrounding area around comfortable. MightyKool is an evaporative air conditioner, so it is not so effective in very humid areas. .

MightyKool, is a 12v evaporative air conditioner made by Swampy Cooling Systems who have been making 12 volt portable cooling systems since 1989. The M400 costs $949 inc shipping, less if ordered online.


Fill up your cooler with ice and turn it into an air conditioner for your boat and boating activities. KoolerAire can be used below deck, or on deck. The KoolerAire fits a 25 qt Igloo or a 28 qt Coleman. The power comes from a car type cigarette adapter. While the ice is cooling your drinks it can keep you cool at the same time. $40 retail 16 1/4 X 9 X 1 1/4 . The fan sucks the cool air from the cooler and spreads it around.

The koolerAire

Turn your cooler into a 12 volt air conditioner! With KoolerAire space saving design air conditioning has become more portable than ever before! Boat Misters

Its attractive compact profile, whisper quiet fan, and low power consumption makes KoolerAire the economical alternative to 12 volt, portable air conditioners costing hundreds of dollars!

Boat Misters

When its hot outside any way of cooling down is worth looking at. Misting is based on the theory of Evaporative Cooling which is the scientific principal of Thermal Dynamics. Water is forced through the specially designed misting nozzles, and a fog of ultra fine water droplets with an average size of 50 microns or less. Installation

Comfort Zone Boat Misting System

The new Comfort Zone Boat Misting System attaches to the boats Bimini or T-Top and emits a cooling mist that reduces on-deck temperatures by up to 30 degrees. The unique mid-pressure pump delivers 150 psi of misting power at the rate of about one gallon of fresh water per hour while only drawing one amp. The system can be used on existing Bimini and T-Tops or designed-in by the boat manufacturer as an integrated system.