A refrigerator does not produce cold but removes heat. An effective means of getting rid of this heat is critical for the refrigerator's performance and energy consumption. Isotherm refrigeration systems use either air or seawater to remove heat.

Air-cooling is a traditional way of removing heat with a condenser where air is blown through by a fan. It is important that the compressor compartment is ventilated, so that cold air enters from below and hot air is allowed to escape above. The lower in the boat the compressor is installed the more "help" it gets from the outside water.

Although heat always rises if left to the laws of nature, the Isotherm SP unit uses the natural movement of the hull to draw heat down and out through a special fitting in the galley sink drain hose.

As this hose is not restricted by pumps or non-return valves, the flow inside is completely free. Each movement of the water surrounding the boat produces a similar change of the water level inside the hose

Isotherm Magnum is designed especially for vessels where refrigeration requirements are exceptionally large or for extended sailing in tropical waters. Isotherm Magnum uses the surrounding water, always appreciably cooler than the air inside the boat, to increase cooling efficiency.

All Magnum models are fitted with integral seawater pumps for circulating the cooling water through the cooling section of the refrigerator compressor. The pump is quiet, self-priming, withstands being run dry and is self-aerating. The highly efficient heat exchanger is manufactured in a corrosion-resistant copper-nickel alloy and fitted with a zinc anode. Seawater systems are unmatched in efficiency and offer increased cooling capacity.