What heater size for a 33 gallon long tank?
48 × 13 × 13 in · freshwater planning
33 gallon long · heater wattage
The working
33 nominal gal × 3 W/gal = 99 W for a mild rise; × 5 = 165 W for a larger rise. At a 10°F rise the rounded choice is 1 × 100 W.
| Temperature rise | Estimated W | Common units / installed W |
|---|---|---|
| 5°F | 99 | 1 × 100 / 100 |
| 10°F | 99 | 1 × 100 / 100 |
| 12°F | 132 | 1 × 150 / 150 |
| 15°F | 165 | 1 × 200 / 200 |
| 20°F | 165 | 1 × 200 / 200 |
First decisions for this medium setup
Before choosing power for 33 gallons, decide where the unit fits with the filter intake and substrate. A horizontal or diagonal installation requires explicit manufacturer permission. During a water change, the waterline can expose the upper part of a vertically mounted heater; unplug it and observe the maker’s cooling instructions.
33 gallon long equipment and layout plan
A low, extended rectangle puts more of the layout along a horizontal swimming lane. The 48 × 13-inch base has an aspect ratio of 3.69:1. A lid or light must span roughly 48 inches; measure rim openings and bracket adjustment before ordering.
| Room-to-target rise | Calculated need | One-unit option | Two-unit option |
|---|---|---|---|
| 10°F | 99 W | 100 W | 50 + 50 W |
| 15°F | 165 W | 200 W | 100 + 100 W |
| 20°F | 165 W | 200 W | 100 + 100 W |
One correctly sized unit keeps installation simple. Two smaller thermostatic units spread heat, but do not make a stuck-on thermostat safe; check temperature independently. The 48-inch span determines how far heat must circulate; the 13-inch height also limits vertical mounting clearance.
Moving up from the 30 gallon changes watts of calculated demand at a 20°F rise from 150 to 165: an increase of 10%. Budget for the larger requirement rather than reusing the smaller plan unchanged.
Assumptions and limits
These bands (3 W/gal up to 10°F, 4 between 10 and 15°F, 5 at 15–20°F) are estimates, not manufacturer guarantees. Covers, drafts and evaporation matter. For rises above 20°F, use the maker’s sizing chart. Split heating above 55 gallons; verify temperature with a separate thermometer. Unplug heaters before exposing them during maintenance.
Adjust measurements with the heater wattage calculator
Questions before you buy
What dimensions does this 33 gallon long calculation use?
It uses a rounded 48 × 13 × 13 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the heater wattage estimate for a 33 gallon long tank?
99–165 W planning range
Equipment to check
Compare adjustable aquarium heater. Check dimensions, capacity and product instructions before buying.
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