The Free On-line Aquaculture Dictionary

Heating Systems

System Type


Immersion heaters

Electrical immersion heaters (like the one in the tank that probably heats your hot water at home) placed either directly into the tank or part of the system are a good method for heating small tanks and systems where either the water is static, or recirculated to a high degree (which has the effect of keeping the heat in the system). Some immersion heaters are available with their own thermostats, others require a separate controller. When using immersion heaters it is advisable to have three or four smaller units rather than one larger unit. This is because if one of the elements fails there will only be a partial heat loss, which will limit the stress on the fish. It is quite feasible to link all the heaters to the same controller unit.

Immersion heaters are most effective if they are mounted horizontally in a tank rather than vertically. This gives a much better distribution of heat through the water. If heating a large static tank it is often advisable to have a small airstone or pump providing some currents to assist in the heat distribution. In smaller thanks, the currents caused by the hot water rising to the surface is often sufficient. 

Immersion heaters can be difficult to control to an exact temperature setpoint and frequently operate with a hysterises of 2-3oC. This is because the electrical elements take time to heat up when turned on and time to cool down when turned off. A programmable controller can be used to give finer control, but the controller must first be “tuned” to the ramp up and ramp down rates of the element. See controllers for more detail


Usually gas or oil fired, boilers use an ignited fuel to heat an enclosed circuit of water. A heat exchanger is then used to transfer this heat to the farms water supply. See diagram heatx.htm 

Boilers are commonly used where large amount of heating are required. They are very simple systems, with mainly just the burner part of the system requiring any special maintenance. Boilers, when properly maintained are also very reliable. A boiler system is very cost effective for a large flow system, when compared to immersion heaters and are also  easier to control the temperature to a given temperature setpoint.


Large electrical heating systems, which operate either in line in a chamber (which makes them like immersion heaters) or on an enclosed loop with a heat exchanger (like the boilers) are also available. These systems are not usually economically viable compared to boilers, except in some countries where electricity is very cheap.