What size breaker for a hot tub?
Short answer: A 240 V hot tub that draws 40 A with the heater and jets on is sized at 125% for a long-running load: 50 A, so a 50 A GFCI breaker on 8 AWG copper THWN-2 in conduit. A spa drawing 32 A needs 40 A; a swim spa drawing 48 A needs 60 A. A 120 V plug-and-play tub runs on a 15 A or 20 A GFCI circuit.
Breaker and wire by spa current
The number that decides the breaker is the total current on the spa's nameplate or in its installation manual, not the heater wattage alone. We size at 125% of that current, the same way NEC 422.13 treats a storage water heater, because a spa heater can run for hours on a cold night:
| Spa | Nameplate current | 125% | Breaker | Copper THWN-2, 75 °C | Copper NM-B |
|---|---|---|---|---|---|
| 120 V plug-and-play, 1 kW heater | 12 A at 120 V | 15 | 15 A | 14 AWG | 14 AWG |
| 120 V convertible, heater and pump together | 16 A at 120 V | 20 | 20 A | 12 AWG | 12 AWG |
| 240 V, 5.5 kW heater and circulation pump | 24 A at 240 V | 30 | 30 A | 10 AWG | 10 AWG |
| 240 V, heater plus one jet pump | 32 A at 240 V | 40 | 40 A | 8 AWG | 8 AWG |
| 240 V, heater plus two pumps or a blower | 40 A at 240 V | 50 | 50 A | 8 AWG | 6 AWG |
| Swim spa or tub with two heaters | 48 A at 240 V | 60 | 60 A | 6 AWG | 4 AWG |
Rating80% (continuous load)AllowedNot allowed: over 80%Over the rating
If the manual lists a breaker size, that is the size to install: the spa was tested and listed with it, and the inspector will check against it. Never put a bigger breaker on a spa than the manual allows.
Why 50 A is the size you see most
A 5.5 kW heater alone draws 22.9 A at 240 V. Add a two-speed jet pump on high and a blower or a second pump, and a typical 240 V tub lands near 40 A, which the 125% rule turns into 50 A: exactly a 50 A breaker. Many spa control packs can also be set up for a smaller circuit by locking the heater out while the jets run on high, which brings the draw down to the 24 or 32 A rows above. The manual shows which setting matches which breaker; the trade-off is that the water cools a little while you use the jets.
Unlike a water heater, most 240 V spas also need a neutral, because the controls, lights and some pumps run at 120 V. That means four wires to the tub: two hots, a neutral and an equipment ground. The ground for a 50 A circuit is 10 AWG copper.
Long runs from the panel
A hot tub often sits at the far end of a yard. The table shows voltage drop at a steady 40 A, 240 V, on the minimum 8 AWG copper and the smallest size that keeps it at 3% or less:
| One-way distance | Drop on 8 AWG | Size for ≤3% | Drop |
|---|---|---|---|
| 25 ft | 0.6% | 8 AWG | 0.6% |
| 50 ft | 1.3% | 8 AWG | 1.3% |
| 100 ft | 2.5% | 8 AWG | 2.5% |
| 150 ft | 3.8% | 6 AWG | 2.5% |
| 200 ft | 5.1% | 4 AWG | 2.1% |
From about 150 feet, 6 AWG keeps the heater and pump motors at full voltage. If you upsize the hot conductors for voltage drop, NEC 250.122(B) requires the equipment ground to grow in the same proportion. Run the numbers for your distance in the voltage drop calculator.
What the heater costs to run
The heater is most of a hot tub's electricity use, and how many hours it runs depends on the cover, the weather and how often the tub is used. At the U.S. average of 18.19¢/kWh (January–July 2026, EIA), 30 days a month:
| Heater | Per hour | 2 h/day | 4 h/day | 6 h/day |
|---|---|---|---|---|
| 4.0 kW heater | $0.73 | $43.66 | $87.31 | $130.97 |
| 5.5 kW heater | $1.00 | $60.03 | $120.05 | $180.08 |
Winter is when those hours climb, and a tight, thick cover saves more than anything else. Check your state's rate on the electricity prices by state pages, or plug your own hours into the appliance cost calculator.
For the same 125% rule applied to a tank heater, see what size breaker for a water heater; every standard rating is listed in standard breaker sizes.
Safety. A hot tub needs GFCI protection and a disconnect within sight of the tub, at least 5 feet away from it, usually a small "spa panel" with a GFCI breaker. NM-B cable is only for dry locations, so the outdoor run is wire in conduit. Water and 240 V are an unforgiving mix: have a licensed electrician install it, with a permit.