Reef Aquarium Heaters & Chillers: 2026 Complete Guide
A stuck heater is the #1 way reef tanks kill themselves. A missing chiller is the #2 way. This guide covers how to size heating and cooling for reef stability at 25–26 °C (77–79 °F), why redundancy is non-negotiable, and how to pick between titanium, quartz, and inline options that actually last.
1. Target Temperature & Why Stability Matters
Coral reefs in nature run between 24 and 28 °C (75–82 °F) depending on latitude. Home aquariums target the middle of that band: 25–26 °C (77–79 °F).
More important than the exact number is stability. A tank running steady at 27 °C will outperform a tank swinging 25–27 °C every 24 hours. Coral metabolism, alkalinity uptake, and zooxanthellae photosynthesis all shift with temperature. Rapid swings stress the coral more than a slightly-warm-but-stable environment.
Rule of thumb tolerances:
- Excellent: ±0.3 °C variation across 24 hours
- Acceptable: ±0.6 °C
- Stressful: ±1.0 °C or more — SPS will show it in 2–4 weeks
- Dangerous: ±1.5 °C plus — tissue browning, RTN, bleaching
2. Heater Sizing: The 3–5 W/Gal Rule
Rough rule: 3–5 watts per gallon of total tank + sump volume. Warmer rooms shift toward 3 W/gal; cooler rooms toward 5 W/gal.
Example: A 90-gallon display + 30-gallon sump in a normal-temperature US home wants 120 gal × 4 W/gal = 480 W total. Two 250 W heaters split the load = 500 W, plenty of headroom.
Undersize on purpose. A heater that's too small runs continuously and rarely reaches an overshoot condition. An oversized heater cycles rapidly and, when it fails stuck-on, cooks the tank faster. Two smaller heaters in parallel is always better than one big one.
3. Heater Types: Titanium, Quartz, Inline
Titanium (the reef standard)
Titanium heating element in a titanium tube. Salt-water safe, effectively unbreakable in reef conditions. Requires an external controller (thermostat) because titanium heaters typically ship without one. Higher upfront cost, longest lifespan (8–15 years reported).
Quartz Glass (the freshwater legacy)
Glass tube with a nichrome heating coil inside. Ships with an integrated thermostat (turns off when target reached). Cheap ($20–$40), reliable if handled carefully.
Downside: glass tube can crack from thermal shock (empty running, sudden cold water top-off) — and a crack means live electricity in your tank. Use ONLY submersible-rated quartz heaters, unplug before doing water changes.
Inline Heaters (the invisible option)
Cylindrical heater plumbed inline with the return pump line. Water flows through it continuously. Nothing in the display or sump; heaters hide in the plumbing.
Best for: rimless / bare-bottom show tanks where visible heaters spoil the aesthetic. Downside: if the return pump fails, water in the heater tube boils. Wire the heater to shut off when the return pump does.
4. The Four Heater Brands That Matter
Cobalt Aquatics Neo-Therm
The reef community's default recommendation. Shatter-resistant polymer body (not glass), integrated thermostat, LED display. Reliable, mid-priced, ships in 25 W to 400 W sizes. 3-year warranty.
Finnex Titanium Heaters
The go-to titanium option. Bare titanium tube requires an external controller (Finnex sells the HC-810M controller separately for ~$50, or use your reef controller). Bulletproof reliability.
Eheim Jager
The freshwater legacy that migrated to reef. Quartz glass with integrated thermostat, decades of reputation, precise temperature calibration. Cheap ($25–$45) but glass = risk of thermal shock. Popular on nano tanks where a full titanium build is overkill.
Aquamaxx Titanium
Alternative to Finnex titanium at a similar price point. Same "requires external controller" model. Choose based on availability.
5. Redundancy: Why You Need Two Heaters
Every experienced reefer has a "boiled tank" story. Modern heaters do fail stuck-on. Even the best brands.
The universal solution: two heaters, both undersized, split across two circuits.
- Buy two heaters sized at half your total load each (e.g., two 250 W for a 500 W target).
- Plug each into a separate outlet strip, ideally on separate breakers if possible.
- Set BOTH thermostats to your target temperature (e.g., 26 °C).
- Add a redundant temperature safety rule on your reef controller: if tank temp > 27 °C for >5 min, cut power to BOTH heater outlets. See the reef controllers guide for exact wiring.
- Add a mechanical thermostat (Ranco ETC-111000, $40) as a third layer. It sits inline before the heater outlets and cuts power at 28 °C regardless of what the controller is doing.
If any one layer fails, the other two catch the problem. This is the difference between "my heater failed" (annoying, no livestock lost) and "my heater failed" (heartbreaking, $3,000 in dead livestock).
6. Chillers: When You Actually Need One
Most reefers overestimate their chiller needs. The equipment in your tank — return pump, powerheads, skimmer, LEDs — produces waste heat. In a room-temperature environment, that waste heat alone can push the tank 2–3 °C above ambient.
You need a chiller if:
- Your ambient room temperature exceeds 27 °C (81 °F) for more than a few weeks per year
- Your equipment heat load consistently pushes the tank above 28 °C
- You're in the tropics (Thailand, Singapore, Indonesia, Vietnam), the American Southwest, or an un-air-conditioned building
You probably don't need a chiller if:
- Your home is air-conditioned to 20–24 °C year-round
- Your equipment heat load pushes the tank max 2–3 °C above room temp
- Cheap fixes work: a clip-on cooling fan blowing across the sump surface can drop temp 1–2 °C via evaporative cooling. Costs $15. Increases ATO consumption.
The order of operations for cooling problems is: fix the source first (LEDs too close, sump enclosed, no ventilation), then evaporative cooling (fan), then chiller. Buying a chiller for a problem that could be solved by a $15 fan is a common mistake.
7. Chiller Sizing & Brands
Chillers are rated in BTU/hr or horsepower. Manufacturers publish sizing charts, but a general rule:
- Nano (10–30 gal): 1/10 HP chiller
- Mid-size (30–90 gal): 1/4 HP
- Large (90–180 gal): 1/3 to 1/2 HP
- Show (180+ gal): 1/2 to 1 HP
The three brands worth knowing:
JBJ Arctica
The affordable-yet-solid choice. 1/10 HP through 1 HP models. Titanium heat exchanger, good reliability, 2-year warranty. Loud — place in a utility room or under-cabinet with ventilation.
Hailea HS Series (Ultra Titanium)
Popular in Southeast Asia (widely stocked in Thailand). Titanium exchanger, quieter than JBJ, wider capacity range. HS-28A covers 60–90g tanks; HS-52A covers up to 200g.
TECO SeaChill
Italian-made, quieter operation, premium construction. Priced 30–50% above JBJ. Best if noise matters (living room installations).
8. Comparison Tables
Heaters
| Model | Type | Sizes (W) | Price (USD) |
|---|---|---|---|
| Cobalt Neo-Therm | Polymer body + integrated stat | 25–400 | $40–$90 |
| Finnex Titanium | Titanium (no stat) | 100–800 | $45–$130 |
| Finnex HC-810M controller | External stat for Ti heaters | n/a | $50 |
| Eheim Jager | Quartz glass + integrated stat | 25–300 | $25–$60 |
| Aquamaxx Titanium | Titanium (no stat) | 100–500 | $40–$110 |
Chillers
| Model | Capacity | Tank size | Price (USD) |
|---|---|---|---|
| JBJ Arctica DBM-150 | 1/10 HP | 20–50 gal | $450 |
| JBJ Arctica DBE-250 | 1/4 HP | 50–90 gal | $700 |
| JBJ Arctica DBE-500 | 1/2 HP | 90–180 gal | $1,050 |
| Hailea HS-28A | ~1/6 HP | 60–90 gal | $450 |
| Hailea HS-52A | ~1/3 HP | 100–200 gal | $700 |
| Hailea HS-66A (popular in Thailand) | ~1/2 HP | 150–300 gal | $850 |
| TECO TC-15 | 1/3 HP | 80–180 gal | $1,050 |
9. Seven Common Mistakes
- Running a single heater. Two undersized heaters >> one big heater. Non-negotiable on any tank holding more than $500 of livestock.
- Trusting the heater's built-in thermostat. The thermostat inside the heater is a mechanical component that fails stuck-on. Always run an external controller as a second layer.
- Skipping the mechanical thermostat backup. A $40 Ranco ETC-111000 wired between wall and heater outlet strip is the last line of defense when your reef controller reboots at 3 AM with the heater on.
- Placing heaters in the display. Fish burn themselves against exposed heaters. Sump only.
- Chiller in an enclosed cabinet. Chillers dump heat — they need airflow. An enclosed cabinet traps the heat and causes short-cycling. Ventilate the cabinet or move the chiller.
- Chiller drop pump too small. Chillers need a specific flow rate (usually 300–600 GPH). Undersized flow makes the chiller short-cycle and fail early.
- No temperature probe redundancy. Your reef controller's temp probe is a single point of failure. Add a second probe (analog thermometer, cheap floating thermometer, or second controller probe) for cross-verification.
10. Our Picks by Tank Size & Climate
Nano (10–30 gal), temperate climate
Single Eheim Jager 100 W ($30) with quartz stat. Nano tanks don't have room for two heaters and their small volume responds fast to thermal issues — wire it through a reef controller for safety.
Mid-size (30–120 gal), temperate climate
Two Cobalt Neo-Therm 150 W ($100 pair) plus a Ranco ETC-111000 mechanical thermostat backup ($40). Skip chiller unless equipment heat pushes above 28 °C consistently.
Mid-size (30–120 gal), tropical climate
Heaters: two Cobalt Neo-Therm 100 W ($90 pair) — they'll rarely run but you need them for AC failure. Chiller: Hailea HS-28A ($450) if your tank consistently sits at 28+ °C without help.
Large (120–250 gal), temperate climate
Heaters: two Finnex Titanium 400 W ($200 pair) + Finnex HC-810M controller ($50). Chiller: JBJ Arctica DBE-250 ($700) if room ambient exceeds 25 °C in summer.
Show tank (250+ gal), any climate
Heaters: two Finnex Titanium 800 W ($260 pair) + Apex or GHL controlling both. Chiller: TECO TC-15 or JBJ Arctica DBE-500 ($1,000+). Always. Show tanks have too much equipment heat to skip this.