What Wattage Aquarium Heater Do You Need, and How Much Filter Flow? Guidelines and Calculations for a 60 cm Tank

The heater guide: about 1 W per litre for a 10 °C difference

Heater wattage depends on how much water you’re heating and how many degrees you need to raise it. A commonly used guide is about 1 W per litre of water when the difference between room and water temperature is 10 °C. For a 15 °C difference it’s 1.5 W and for 20 °C it’s 2 W, increasing in proportion to the difference.

• Required watts = real water volume (L) × temperature difference (°C) ÷ 10
• Without a lid, heat escapes more easily from the surface, so allow about 1.3 times as much
• Don’t choose exactly the calculated value; pick the nearest commercially available wattage at or above it
• In large tanks needing more than 150 W, splitting it between two heaters means the water won’t cool suddenly if one fails

The water volume to use here is the real volume, not one based on the outside dimensions. For a standard 60 cm tank, calculate with about 51.5 L with 4 cm of Oiso gravel, not the 64.8 L from its outside dimensions. How to work out the volume is explained in your tank’s real water volume.

Heater chart by tank size and room temperature

For a target water temperature of 25 °C, this chart shows the wattage needed for each winter room temperature and the heater to choose (calculated with the water volume for 4 cm of Oiso gravel and a lid). Tank sizes are standard Japanese sizes.

For a standard 60 cm tank, you need about 52 W at a room temperature of 15 °C and about 77 W even at 10 °C, so one 80 W heater is enough. If the heating is turned off and the room drops to near 5 °C, you need about 103 W, so 120 W is the guide. If in doubt, go one size up and set the water temperature with the thermostat. Even if the wattage is on the high side, the thermostat stops the water getting too hot.

Filter flow: turn the tank’s water over 5–10 times an hour

Think of a filter’s strength in terms of how many times per hour it can filter the tank’s water (the turnover). A common guide is 5–10 times an hour. For a standard 60 cm tank (about 51.5 L), that’s about 258–515 L per hour, or about 4.3–8.6 L per minute.

• The flow on the box is the maximum with no hoses or media. In use it drops by 20–30%, so choose from the middle to the top of the range
• Some pumps give different flow on 50 Hz and 60 Hz mains power (in Japan, east and west differ). Check the figure for where you live
• Goldfish and planted tanks need more flow; betta, fry and medaka need gentler flow
• A canister filter holds more media as well as moving water, so it keeps water more stable than a hang-on filter with the same flow

Estimating a heater’s electricity cost

A heater doesn’t draw power all the time; it switches on only when the water drops below the set temperature. Electricity cost is “W ÷ 1000 × hours switched on × price per kWh”. At Japan’s guideline price of 31 yen/kWh, the cost for an 80 W heater by daily hours switched on is as follows.

Multiply the kWh by your own electricity price to get the cost where you live. How long the heater runs varies a lot with room temperature and whether there’s a lid. Just covering the tank to cut heat loss from the surface and moving it away from a window shortens the running time. Comparing it with heating appliances is covered in comparing heater electricity costs, and the formula itself in how to calculate electricity costs.

Using a heater safely

• Unplug it before lowering the water for a water change. If a heater runs out of the water, it can overheat and crack or scorch things around it
• Place the heater where the water flow hits it, not buried in the substrate. Where the water moves, the whole tank stays at an even temperature
• Choose one with a guard so fish can’t touch it and get burned, especially in tanks with fish that cling to surfaces, such as plecos
• Put in a separate thermometer and check every day that the temperature matches the setting. You’ll notice a faulty heater sooner
• Heaters wear out. Many manufacturers recommend replacing them every 1–2 years, so check yours in autumn to be ready for winter

In summer the opposite can happen and the water gets too hot; above 30 °C, many fish are under strain. As well as unplugging the heater, plan other measures such as opening the lid, using a cooling fan or running the room’s air conditioning.

FAQ

What wattage heater does a 60 cm tank need?

To keep a standard 60 cm tank (real water volume about 51.5 L) at 25 °C, you need about 52 W at a room temperature of 15 °C and about 77 W at 10 °C, so 80 W is the guide. If the room drops to near 5 °C, choose 120 W.

Is a heater with too much wattage a problem?

If a thermostat controls the water temperature, a large heater won’t make the water too hot. But if it fails and won’t switch off, the effect is bigger, so avoid ones that are far too large, and in big tanks it’s safer to split the wattage between two heaters.

How much filter flow do I need?

A flow that turns the tank’s water over 5–10 times an hour is the guide. For a standard 60 cm tank, that’s about 258–515 L per hour. The figure on the box is the maximum and drops by 20–30% in use, so choose from the middle to the top of the range.

How much does an aquarium heater cost to run per month?

An 80 W heater switched on for 12 hours a day uses 0.96 kWh a day, about 28.8 kWh a month. At 31 yen/kWh that’s about 30 yen a day and about 893 yen a month. The actual running time varies with room temperature and whether there’s a lid.