Three heaters worth buying for a betta tank. One preset, two adjustable. All priced $20 to $40. Affiliate disclosure at our affiliate disclosure. Temperature targets follow the Merck Veterinary Manual aquarium-fish reference.
Quick recommendations
| Heater | Wattage | Type | ~Price | Best for | Buy |
|---|---|---|---|---|---|
| Fluval P25 | 25W | Preset 76–78°F | $25 | Default 5-gallon | Amazon |
| Eheim Jager 25W | 25W | Adjustable | $35 | Breeders, wild keepers | Amazon |
| Cobalt Neo-Therm 25W | 25W | Adjustable | $40 | Flat-shape preference | Amazon |
1. Fluval P25 preset
The default. Preset to 76–78 °F. No user adjustment needed. Built-in thermostat. LED status indicator. Shatterproof polymer casing, not glass.
Pros:
- Set-and-forget.
- Reliable thermostat across years of use.
- Compact; rated for tanks up to 6 gallons.
- Shatterproof polymer casing.
Cons:
- No adjustment. Holds 76–78 °F, not a user-selectable point.
- Single point of failure (if it fails on, it overheats).
Use with a thermometer as sanity check.
Check price on Amazon Affiliate link. See our disclosure.
2. Eheim Jager 25W adjustable
German build quality. Adjustable from 65 °F to 93 °F. Used by most serious aquarists.
Pros:
- Adjustable range useful for breeders and wild species.
- Decade-long reliability track record.
- Recalibration possible.
Cons:
- Larger than preset options.
- Adjustable means potential for misadjustment.
- Slightly higher price.
Check price on Amazon Affiliate link. See our disclosure.
3. Cobalt Neo-Therm 25W adjustable
Flat rectangular shape vs. cylindrical.
Pros:
- Flat shape fits nano tanks better.
- Adjustable.
- Shatter-resistant.
Cons:
- Priciest of the three.
- Less track record than Eheim.
Check price on Amazon Affiliate link. See our disclosure.
What wattage for what tank
- 2-5 gallon: 25W.
- 5-10 gallon: 25W or 50W (25W runs more often in 10 gal; 50W cycles less).
- 10-20 gallon: 50W.
- 20-40 gallon: 100W.
Use a larger heater than you need if your room temperature fluctuates (basement, garage conversion). Smaller heater in a stable warm room.
What to avoid
Sub-$10 Amazon unbranded heaters. Thermostats fail. Multiple reported cases of stuck-on heaters cooking tanks.
Suction-cup-only mounts that come loose in soft water. Check daily during first week of use.
Heaters rated for larger tanks than you have. An oversized heater with a weak thermostat overshoots in a small tank.
Heaters without a thermostat at all. Aquarium “heating elements” without feedback control should be illegal for indoor pet use.
Installation best practices
- Place heater horizontally near the filter outflow for even distribution.
- Submerge fully. Verify waterline above “MIN” marking.
- Let equilibrate 30 minutes before turning on.
- Verify temperature with an independent thermometer for the first week.
- Replace every 3-5 years regardless of apparent function. Thermostats degrade.
The temperature target
Pet betta: 77-80 °F (25-26.5 °C). Preset at 78 is the sweet spot.
Breeding: 80-82 °F (27-28 °C).
Wild species: 75-78 °F (24-25.5 °C). Some highland species lower.
The thermometer is not optional
A $3 stick-on thermometer or glass thermometer is insurance against heater failure. Check it whenever you check the tank. Noticeable drift from setpoint is the early warning of a failing heater.
Budget backup
If budget forces a cheaper option, the Hygger 25W adjustable titanium heater (~$19–22) is the best sub-$25 choice in 2026. It is adjustable, not preset. Set it to 78 °F, verify with a thermometer on day one, and check weekly. Slightly less reliable than the Fluval P25, but acceptable with vigilant monitoring. Not recommended as first choice; recommended if $25 isn’t in the budget.
Check Hygger 25W heater on Amazon Affiliate link. See our disclosure.
The warm-room alternative (almost never)
Some hobbyists keep tanks in rooms stable at 26 °C year-round and skip heaters. Only viable if:
- Room thermostat holds within 1 °C.
- HVAC failure doesn’t drop the room below 23 °C ever.
- Summer AC doesn’t cool the room below 23 °C.
For most settings, dedicate a heater to each tank. Don’t rely on room temperature control.
Heaters are the cheapest piece of essential betta gear. Buy once, buy well, replace on schedule. A $25 heater across a 4-year fish life is $6 per year. Budget for it.
Related on this site
- Betta Tank Setup: A 5-Gallon Minimum Build, Step by Step
- Best 5-Gallon Betta Tanks in 2026
- Best Betta Pellets in 2026: Four That Don’t Embarrass Themselves
- Best Live Plants for Betta Tanks in 2026
- Betta Buyer’s Guide: What NOT to Buy
Frequently asked
- Do bettas really need a heater?
- Yes. Sub-24 Celsius water suppresses betta immunity and invites fin rot, columnaris, and other cold-opportunistic diseases. Unless your room is a stable 26 Celsius year-round, heat the tank.
- Preset or adjustable?
- Preset (78 F) is simpler and safer. Adjustable is useful if you breed (need 27-28 C) or keep wild species (need lower). Preset is the correct default for pet-keepers.
- What size wattage?
- Rule of thumb: 5 watts per gallon. 5-gallon tank needs 25 watts. 10 gallons needs 50. Undersized heaters run constantly and fail early.
- Why not the cheap 10 dollar heaters?
- They fail stuck-on at abnormally high rates. A stuck-on heater cooks the fish. Spend 25 dollars for a heater that has a reliable thermostat.