Heater size for a 29 gallon tank
A 29-gallon is 18 inches tall on a 30 × 12 inch footprint and holds about 25 gallons of real water. A 100 W heater covers most rooms.
Watts needed by room temperature
For 78 °F (25.6 °C) water in a lidded glass tank holding 25.1 gallons of real water:
| Coldest room | Lift | Heat needed | Buy | One heater | Two heaters |
|---|---|---|---|---|---|
| 73 °F (22.8 °C) | 5 °F (2.8 °C) | 38 W | 50 W | 50 W | 2 × 25 W |
| 68 °F (20.0 °C) | 10 °F (5.6 °C) | 75 W | 100 W | 100 W | 2 × 50 W |
| 63 °F (17.2 °C) | 15 °F (8.3 °C) | 113 W | 150 W | 150 W | 2 × 75 W |
| 58 °F (14.4 °C) | 20 °F (11.1 °C) | 150 W | 200 W | 200 W | 2 × 100 W |
"Buy" is the calculator's recommendation: the heat needed rounded up to a common heater size (10, 25, 50, 75, 100, 150, 200, 250, 300 W). For an open top add about 25%; for acrylic take off about 15% — or use the calculator above with your own temperatures.
One heater or two?
One 100 W heater covers a 10 °F lift. A two-heater setup would be 2 × 50 W — worth considering for long tanks, valuable fish or as a backup if one heater fails.
If a heater's thermostat sticks on, the worst case (every watt going into the water, none lost to the room) is a rise of about 1.6 °F per hour with one 100 W heater, or 0.8 °F per hour with one 50 W heater of a pair. Real tanks lose heat, so the rise is slower, but it shows why an oversized heater is riskier in a small tank. An external controller cuts power if the water passes your set point.
29 gallons in liters, and the real water
| Tank | Outside dimensions | Rated | Real water |
|---|---|---|---|
| 29 gallon | 30 × 12 × 18 in (76.2 × 30.5 × 45.7 cm) | 28.1 gal (106 L) | 25.1 gal (95 L) |
29 US gallons is 109.8 liters (24.1 imperial gallons). Real water is inside the glass, filled 1 inch below the rim; the heater rule above uses it.
Heating a tall 29
The 29-gallon is the 20 long's footprint with 6 more inches of height, so its heat loss comes mainly through tall glass walls. Two things follow:
- Place it low and in the flow. Warm water rises; a heater near the surface can leave the bottom a degree or two cooler where corydoras live. Mount it low, diagonally, beside the filter intake or under the outflow.
- Size up for an open top. Many keepers run 29s without a lid for plants; evaporation from 360 square inches of surface adds about a quarter to the heat needed.
The common 3–5 W per gallon rule would suggest roughly 90–145 W; the calculated value for a 10 °F lift lands at the low end of that range, which matches typical recommendations of about 100 W for a lidded 29.
How the numbers are worked out
watts = real gallons × lift (°F) × 0.3, about 0.14 W per liter per °C, for a lidded glass tank. For a 10 °F lift that is 3 W per gallon — the low end of the familiar 3–5 W per gallon rule of thumb, which is commonly quoted for heating up to about 10 °F above the room with a lid. That rule would put a 29 gallon tank at 87–145 W. Use the coldest overnight temperature, not the daytime average, and go one size up for drafty rooms. Read the heater size guide for placement and safety.
More about this size: 29 gallon. Other sizes: 3 gal, 5 gal, 10 gal, 20 gal, 40 gal, 55 gal, 75 gal · full chart.
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FAQ
How many watts per gallon does a 29 gallon tank need?
About 3.0 W per gallon of real water to hold 78 °F in a 68 °F room (0.3 W per gallon per °F of lift), which rounds up to 100 W. In a 58 °F room it rises to 200 W.
Is 100 W enough for a 29-gallon tank?
Yes for a lidded tank in a room about 10 °F below the water. For a room 15 °F colder or an open top, use 150 W.
Should I use two heaters in a 29-gallon?
It is optional. Two 50 W heaters give redundancy if one fails, but one 100 W heater with a thermometer is the usual setup at this size.
How many liters is a 29 gallon tank?
29 US gallons is 109.8 liters. Filled about an inch below the rim, the tank holds about 25.1 gallons (95 L) of real water, which is what the heater has to warm.