A chiller that is too small never gets the tank down to temperature. It runs all day, wears out early and still loses to a hot afternoon. One that is far too big costs more than the job needs.
This calculator works out the cooling your tank needs. Enter the water volume, how hot the water gets, where you want it, and what your pumps and lights add. It gives you a minimum cooling rating in watts and lists the chillers that cover it.
Aquarium chiller size calculator
How the calculator works
Two things set the cooling you need.
The first is the water. One litre takes 1.163 watt hours of cooling to drop by one degree. A 200 litre tank that has to come down 6 °C holds about 1,400 watt hours of heat to remove.
The second is your equipment, which keeps adding heat while the chiller works. A pump inside the tank turns all of its wattage into heat in the water. A pump outside the tank adds far less, about a fifth. LED lights add about a quarter of their wattage, and T5, metal halide or power compact lights about 60 percent. Those shares come from a hobby source (a reef calculator citing BeanAnimal’s ReefCentral article), not from a chiller maker, so read them as good estimates.
The calculator asks for the water to come down within 8 hours. That is my own planning target, not a Teco figure. A chiller cools at its rated watts minus the heat your equipment keeps adding, so:
Chiller rating needed = equipment heat + (litres × 1.163 × degrees to drop ÷ 8)
Reading the result
The result is a minimum. It leaves out heat that comes through the glass and water lost to evaporation, and both climb on a hot afternoon with sun on the tank. If your tank sits in a warm room, take the next size up.
Two worked examples:
| Tank | Water | Equipment | Heat from equipment | Rating needed | Chiller |
|---|---|---|---|---|---|
| 200 L freshwater | 32 °C down to 26 °C | 100 W internal pump, 60 W LED | 115 W | 290 W | Teco TK 500, about 3.9 hours |
| 600 L reef with sump | 33 °C down to 26 °C | two 40 W powerheads, 120 W return pump outside, 250 W LED | about 167 W | 780 W | Teco TK 2000, about 6.9 hours |
What the Teco ratings mean for a real tank
Model names and litre figures hint at tank size. Watts are the number that counts.
| Model | Cooling rating |
|---|---|
| Teco TK 500 | 470 W |
| Teco TK 1000 | 660 W |
| Teco TK 2000 | 870 W |
| Teco TK 3000 | 1,730 W |
| Teco TK 3000 with heater | 1,730 W, with a heater built in |
The TK 500, TK 1000 and TK 2000 figures are from Teco’s data sheet for the 230 V / 50 Hz units, measured at a 30 °C room and 25 °C water. For the TK 3000 the table uses 1,730 W, worked out from Teco’s catalogue test at the same 30 °C room and 25 °C water (720 W of power at a coefficient of performance of 2.4). One Teco sheet lists 2,200 W for it under a different test condition, so I went with the lower figure. Teco’s own pull-down tables for the TK 500 and TK 1000 assume a light heat load of about 0.5 watts per litre. A reef tank with big pumps and strong lights carries more than that, so go by the watts, since the litre label can mislead.
The TK 500, TK 1000 and TK 2000 want 500 to 800 litres an hour through them, and the TK 3000 wants 3,000 to 4,000, so check your pump can supply that before you buy.
Common questions
Why does the calculator ask for pump and light wattage? Because that heat arrives all day. A chiller rated only for the water in the tank cools it once and then falls behind.
What if my room is hotter than 30 °C? The chiller’s rating drops as the room warms, so choose a size above the number the calculator gives. A well-sized chiller switches on and off instead of running flat out.
Do I still need a heater? Yes, in winter. A chiller only cools. The heater wattage calculator sizes that side.
Related calculators
- Water volume calculator for tank and sump, to get the litres figure used above
- Pump flow guide, since pump wattage adds heat
- All aquarium calculators
- Aquarium chillers
