Marine Refrigeration Systems

Isotherm has a complete range of easy to install ice box conversion kits for sail and power boats

Isotherm COMPACT Marine Refrigeration Systems


Isotherm COMPACT Marine Refrigeration Systems are designed to provide reliable cooling and low power consumption for ice box conversion from 2 to 21 cubic feet.  Isotherm has the largest range of refrigeration and freezer conversion kits and makes it easy to select the proper system for your boat.

Isotherm ice box conversion kits come complete with compressor, evaporator, thermostat, mounting bracket or plate, and are fully charged with quick-connect, self-sealing valves for easy installation. 

Isotherm Marine Refrigeration Systems are available with your choice of flat evaporator plates which can be bent to fit any ice box, "O" shaped evaporators which make convenient freezer sections while cooling the remainder of the box, or stainless steel holding plate ASU systems.  

Isotherm Marine Refrigeration Systems are available as air cooled or water cooled by either the patented SP thru-hull or the Magnum water pump.


Isotherm makes fridge selection easy!

The following illustration shows part numbers and benefits of the Isotherm solutions for a typical 7 foot refrigerator ice box conversion project:

AIR COOLED:  Benefits include lower price, easy to install (no water supply or thru-hull).  Considerations: Ventilation is the key to proper performance of the air cooled system.  Be sure to install the compressor in a dry location with a path for warm air to rise up and out at the top of the compartment and a path for cool air to enter at the bottom of the compartment. With this, a natural convection will be created for efficient operation of the system.

“O” evaporators provide a space to keep frozen goods and make ice.  “O” evaporators come complete with a door to make a freezer compartment like one would find in a cabinet refrigerator.  Flat evaporators provide more surface area creating more even temperatures in the fridge.  Flat evaporators can be bent at any point were the refrigerant channels are straight (not in checkerboard areas).  A bending tool is included with all flat evaporators which is a wood dowel with a notch which provides a radius to push the evaporator around for the perfect bend. Evaporators are recommended to be installed high in the box as cold fills a box like water fills a bucket.  The evaporator can be installed in any orientation.


Compact "2501", Large O-evap. (10.7 x 15 x 5.5), Click-on Bracket & Lid, Air Cooled, 7 cu.ft fridge or 2.3 cu. ft. freezer



Compact "2016", Large flat-evap (7.5 x 47.2), Click-on Bracket, Air Cooled, 7 cu.ft. fridge or 2.3 cu. ft. freezer


SP WATER COOLED:  Benefits include freedom from ventilation issues, maximum efficiency.  Considerations: installing the thru-hull requires boat out of water.



SP "2551" Water Cooled, Large O-evap (10.7 x 15 x 5.5), Click-on Bracket & Lid, 7 cu.ft fridge or 2.3 cu.ft. freezer



SP "2554" Water Cooled, Large flat-evap (7.5 x 47.5), Click-on Bracket, 7 cu.ft. fridge or 2.3 cu.ft. freezer


MAGNUM WATER COOLED:  Benefits include maximum cooling capacity for volumes up to 21 cubic feet, freedom from ventilation issues.  Considerations: water supply from thru-hull like an air conditioner uses. Each pump.  Some boaters will use water from boat’s fresh water tank by installing supply and return barbs screwed into the sides of the tanks.  This eliminates issues with micro-filtering and electrolysis in salt water.  Does not appreciably change the temperature of the water.



Magnum "2505" Water Pump Cooled, Large O-evap (10.7 x 15 x 5.5), Mounting Plate & Lid,  7 cu.ft. fridge or 2.3 cu. ft. freezer



Magnum "2512" Water Pump Cooled, Large flat-evap (7.5 x 47.5), Mounting Plate, 7 cu.ft. fridge or 2.3 cu.ft. freezer


ASU HOLDING PLATE:  Benefits include maximum battery savings under typical cruising conditions where a ‘surplus’ supply of voltage is available from solar panels or when an engine is running.  During these times, the compressor runs at maximum speed to chill the plate quickly which then acts like an artificial block of ice.  When on battery alone, the compressor runs at slow speed and the cold in the holding plate is used first to keep the box at temperature.  Considerations: cost is higher due to advanced electronics and stainless steel holding plate.



ASU "3701" Air Cooled, Refrigeration Unit, Medium holding plate 7 cu.ft. fridge



ASU "3751" SP-Water Cooled, Refrigeration Unit, Medium holding plate for 7 cu.ft. fridge



ASU "4201" Magnum Sea Water Cooled, Refrigeration Unit, Medium holding plate for 7 cu.ft. fridge


ISOHERM SMART ENERGY CONTROL (ISEC):  Based on the ASU technology, the ISEC monitors available voltage and runs the compressor at high speeds when there is a ‘surplus’ (13+ volts) of voltage.  The ISEC has a temperature sensor probe and reduces the operating temperature in the fridge (this ‘delta’ can be adjusted via the knob ‘potentiometer’ and the dip switches that can be set for the purpose (fridge or freezer) and volume.   The ISEC is an affordable method to simulate the effects of ASU by storing the cold in the food and beverages vs. a holding plate.  When on regular battery (12 volts), the ISEC runs the compressor at slow speed and allows the temperatures to rise to normal fridge temperatures, thus saving battery usage.  NOTE: The ISEC module only fits on the DC only Danfoss/SeCOP module.

Here’s a link to a video showing how to install the ISEC in an Isotherm Cruise Elegance cabinet fridge:  

All Isotherm systems are backed by a 5-year limited warranty on the compressor, two years on all other parts, and come complete with mounting bracket for compressor, thermostat, pre-charged evaporators/plates, and 6 feet of refrigerant line (extensions of 1,2, and 3 meters are available).  Isotherm makes it simple to shop for the system best suited for your boat and cruising style by recommending a volume for fridge and/or freezer with choice of air, water SP, and water Magnum (pump) cooling.

Here is a link to a post from an Isotherm ASU SP owner and his experience installing and using the system: