Equipment
Aquarium heater
Heater watts from tank gallons and how cold the room actually is.
Dual heaters (failover)
Use the coldest temperature your room actually reaches overnight in winter — not a comfortable daytime average.
Results
Recommended
150W
Temp lift
10°F
Rule of thumb
3.5W/gal
Shop sizes
150 / 200W
Typical tropical setup in a heated home. Prefer a heater with an accurate thermostat and a digital thermometer to verify.
How to use this
- Enter true water volume (substrate and decor displace water — use our Tank Volume tool if unsure).
- Set the temperature you want for your livestock (most tropical community fish: 76–78°F).
- Enter the coldest ambient temperature the room reaches, then choose single or dual heaters.
- Buy a heater at or slightly above the recommendation; place a separate thermometer away from the heater.
Sizing basis
- ΔT = target − room (°F)
- ≈2.5–6.5 W/gal depending on ΔT (larger lift → more watts)
- Dual mode sizes each heater ~60% of the single-heater total
Tropical tank, heated home (78°F target, room 68°F)
A 10°F lift uses 3.5 W/gal, then we round up to a stock wattage. If the room hits 60°F at night, run the calculator — a 20 long jumps from 75W to 150W.
| Tank | Minimum watts | Usual buy |
|---|---|---|
| 10 gallon | 50 W | 50 W, or 2× 25 W |
| 20 long | 75 W | 75–100 W |
| 29 gallon | 125 W | 150 W |
| 40 breeder | 150 W | 150–200 W |
| 55 gallon | 200 W | 200–250 W, or dual 150 W |
Worth knowing
- Fully submersible heaters should sit horizontally near filter outflow for even heat.
- A heater guard protects fish (and the glass tube) in cichlid or large-fish tanks.
- Controllers that sit inline with the heater add a second thermostat layer against stuck-on failures.
Usual mistakes
- Sizing for summer room temps, then freezing livestock in winter.
- One giant heater with no backup in an expensive display tank.
- Trusting the heater dial alone — always verify with an independent thermometer.
See also: Tank Volume · Water Change · Filter Flow