Result
100 watts
For a 10 deg F temperature rise, start around 100 watts.
- Temperature rise
- 10 deg F
- Recommended heater
- 100 W
When to use two heaters
Large tanks often do better with two smaller heaters placed apart. That can improve heat distribution and add redundancy.
Watch real tank temperature
Room drafts, lids, flow, and heater placement affect real performance. Use a thermometer after setup.
Formula and assumptions
This calculator uses the inputs above to turn a practical planning question into a usable estimate. The result should be treated as a starting point, because product ratings, room conditions, material waste, and real-world use can vary.
Example calculation
Example inputs: Tank volume: 20 gallons; Room temperature: 68 deg F; Target water temperature: 78 deg F. With those values, the calculator returns 100 watts. For a 10 deg F temperature rise, start around 100 watts.
Common planning mistakes
Avoid using rough guesses for every input, forgetting waste or safety margin, and treating the estimate as a guaranteed final number. Measure the space, round up when buying materials or equipment, and compare the result with product labels or project instructions.
FAQs
Aquarium Heater Size Calculator questions
Can a heater be too powerful?
A thermostat controls normal operation, but extreme oversizing can heat too quickly if something fails.
Should I size for winter room temperature?
Yes. Use the coolest normal room temperature the aquarium will experience.