Choosing a Boat AC Unit: Types, Tips & What to Know
If you’ve spent any time on a boat during a warm spell, you’ll know how quickly cabins can become uncomfortably hot—especially when moored in a sheltered marina with little breeze. Whether you’re planning longer coastal trips, liveaboard cruising, or just want more comfort during summer weekends, installing a boat AC unit can make a big difference.
In this guide, you’ll learn what types of boat air conditioners are available, and the key factors you’ll need to weigh up before choosing the right unit for your vessel.
Why Consider an Air Conditioning Unit for Your Boat?
Long summer days on the water are what boating is all about, but when the cabin turns into a sauna, the experience quickly loses its charm. A well-chosen AC unit for boat keeps the interior cool and comfortable, especially overnight when stuffy air can disrupt your sleep.
But there’s more to it than just temperature. Good air conditioning also helps manage humidity, which protects soft furnishings, timber trim, and electronics from mould, mildew and corrosion.
Some systems even double as dehumidifiers, running in dry mode during winter to prevent condensation and damp when your boat is closed up. That’s useful not only for comfort but for preserving your investment in the long run.
Types of Boat Air Conditioning Units
A boat air conditioner can be as small as a self-contained shoebox or as complex as a ship-wide chilled-water plant. Most of them are fixed marine systems that use water from the sea or lake to cool air consistently, but their methods differ. You’ll find plug-and-play portable AC units as well. Let’s take a closer look:
Self-Contained Units
Self-contained units combine everything—compressor, water-cooled condenser, evaporator, and blower—into one compact package. These typically install under a berth or inside a locker near the area they’ll be cooling.
Because plumbing and electrics are housed together, installation is relatively straightforward and affordable. You don’t need to run long refrigerant lines or complex ducting, which makes this type ideal for smaller boats up to around 12 metres.
Pros:
Lowest purchase and fitting cost
Easy to maintain or replace individually
Some models offer reverse-cycle heating for cooler months
Cons:
All the noise from the compressor stays inside the cabin
Limited to cooling nearby spaces—performance drops over long duct runs
Split Systems
Split systems separate the compressor and condenser from the air handler (which sits in the cabin). The noisy components go in an engine room or lazarette, while the cabin gets a quieter unit that handles cooling. They are connected by insulated copper pipes that carry compressed refrigerant.
This setup is perfect for mid-sized boats (12–24 m) with multiple cabins, offering quieter operation and the ability to control each space independently.
Pros:
Quieter cabins thanks to remote compressor
Flexible zoned cooling across different rooms
Typically more energy-efficient than self-contained systems
Cons:
More complex and expensive to install
Requires a qualified technician for refrigerant lines
Efficiency can suffer if installation isn’t carefully planned
Chilled Water Systems
Chilled water systems are typically used on larger yachts (20+ m) and commercial craft. A central chiller cools a loop of freshwater that runs throughout the boat to individual air handlers in each room. These systems are scalable and ideal for complex, multi-zone setups.
Pros:
Scalable for larger vessels
Extremely quiet operation in cabins (only a small fan and coil locally)
Unlimited zoning and fine-grained digital control; handlers can be shut down in unused rooms without affecting the rest of the boat.
Lower electrical load per unit when managed properly
Cons:
Highest upfront and installation cost
Takes up more space and requires professional design
Maintenance is more involved due to water chemistry and pump systems
Portable AC Units
Portable AC units bundle the compressor, evaporator and condenser into a single box and vent hot air through a flexible hose led out of a hatch or portlight. Their plug-and-play nature removes the need to cut through bulkheads or fit seawater pumps, making them popular on charter boats and with owners who can’t modify the hull.
Because installation is as simple as parking the unit on the cabin sole and running the duct topside, you can move it between cabins—or take it home for winter use. Many now accept shore-power, 12/24 V sockets or an onboard battery pack, so you’re not tied to a marina pedestal.
Pros:
No installation required—truly portable
Can be moved between cabins or even taken home
Ideal for small boats, short trips, or temporary use
Runs off battery, mains or solar power
Cons:
Less efficient than built-in systems
Limited to cooling small spaces
Feel like plug-and-play cooling is for you? The EcoFlow WAVE 3 Portable Air Conditioner is one of the best portable AC units for boat. It packs 6,100 BTU of cooling and 6,800 BTU of reverse-cycle heating in a compact 15.6 kg chassis, enough for most fore cabins or saloons up to about 10 m³.
A 1 kWh LFP add-on battery gives two to eight hours of cordless operation, perfect for quiet nights at anchor. Shore mains, vehicle sockets or up to 400W of solar can recharge the pack, letting you harvest energy underway or alongside.
Wi-Fi/Bluetooth app control, R290 refrigerant with a lower global-warming potential, IPX4 splash protection and a measured 44–58 dB sound rating round out a spec list tailored to marine use.
EcoFlow WAVE 3 Portable Air Conditioner
Factors to Consider When Choosing a Boat AC Unit
Choosing the right AC unit is about finding a system that suits your boat, cruising habits, and onboard power setup, without turning installation or maintenance into a headache. Here are the key factors to weigh up before making your decision:
Cabin Size and Cooling Capacity
Cooling power is measured in BTU per hour, and the right size depends on the volume of your cabin. As a general rule, you’ll need around 100–135 BTU per cubic metre, adjusted for warmer climates or cabins with large windows.
For example, a 3×3×2 m cabin in the UK might need 6,000 BTU, while the same space in the Med may call for closer to 8,000 BTU.
Power Supply and Electrical Load
Your boat’s electrical system must handle both the steady running load and the higher start-up surge. Many marinas supply 230 V at 16 or 32 amps—so if your AC unit draws 12 amps, there’s still room for other devices. If you’re relying on a generator or battery bank, look for systems with soft-start or inverter-driven compressors to reduce power spikes.
Energy Efficiency
A higher Energy Efficiency Ratio (EER or SEER) means your AC uses less power to deliver the same cooling. That’s a major plus for boats on limited shore power or when running off a generator. Features like variable-speed compressors and well-insulated ducting can make a big difference to your fuel bill and noise levels.
Heating and Seasonal Use
Many marine AC units are reverse-cycle, meaning they can also heat the cabin when water temperatures are above 4°C—handy for early spring or autumn cruising. If you don’t need heating, a cooling-only unit is simpler and more cost-effective.
Space and Installation
Before you buy, double-check your available space. A compact self-contained unit might tuck neatly under a berth, but split and chilled-water systems need more room for compressors, pumps, ducting or piping. Make sure there’s space for airflow, servicing, and filter changes without tearing the interior apart.
Noise and Vibration
All systems make some noise—especially self-contained units, where the compressor is inside the cabin. These can easily run above 60 dB. Remote compressors or chilled-water setups can bring that down to below 30 dB in the cabin, especially with proper insulation and low-speed fans. For quiet overnight use, low noise should be a priority.
Humidity Control and Condensation
Good AC not only cools—it helps manage humidity, too. That’s important for preventing mould, damp, and damage to woodwork or electronics. Make sure condensate drains properly or install a removal pump if needed. Easy-to-clean filters and accessible seawater strainers also help with long-term upkeep.
Maintenance and Service Access
Like most marine systems, AC needs regular attention: checking pumps, strainers, and anodes, as well as flushing coils and cleaning ducts. Choose a unit with accessible components and available spare parts, ideally from a brand with UK-based support.
Budget and Long-Term Value
Finally, think beyond the initial price. A cheaper unit may suit a day boat perfectly, but on a cruiser with multiple cabins, a split or chilled-water system could offer quieter performance, more comfort, and even help with resale value later on.
Conclusion
A well-chosen boat AC unit can transform your time on the water. It keeps your space comfortable, reduces mould and moisture, and lets you enjoy the boating season without dreading hot, stuffy cabins.
By understanding how each type works and what factors matter most—like boat size, power availability, and installation needs—you’ll be better equipped to make a choice that fits both your vessel and your budget. Take the time to plan properly, and you’ll be rewarded with cooler days, better sleep, and a much more enjoyable experience afloat.
FAQs
Is there AC on boats?
Yes, many boats—especially larger yachts and cruisers—are equipped with air conditioning systems. These range from small, self‑contained units to more complex setups like split AC or chilled‑water systems. Even modest vessels often feature compact marine AC units that combine compressor, condenser and evaporator in one box.
Water from the sea cools the condenser, while a fan blows chilled air into the cabin. There are also portable ACs for boats plugged into shore power or run via an inverter from onboard batteries. The key is matching the unit size to cabin volume for effective cooling.
Does a boat use AC or DC?
Boats typically have both AC and DC systems: DC (direct current) comes from 12V or 24V battery banks and powers lights, instruments and pumps. AC (alternating current) usually arrives from shore power (when docked) or a generator and runs larger appliances like air conditioning or refrigerators.
Traditional marine AC units run directly on AC. However, there’s increasing availability of DC‑powered marine air conditioners (12V or 24V), which can run quietly and efficiently from batteries without needing an inverter.
Do water AC units work?
Yes, marine “water‑cooled” AC systems are the norm and work very well. These systems use seawater (or lake/river water) to absorb heat from the AC’s condenser via a heat exchanger, then discharge it overboard.
They’re reliable, efficient and generally quieter inside the cabin because the noisy heat exchanger is outside or below decks. For larger vessels, chilled‑water systems circulate cooled freshwater through air handlers in different cabins—a highly effective and flexible solution. As long as the sea‑water pump is working properly, these systems keep cabins comfortably cool.