What Size Generator for a Hot Tub?
A 9,500W portable with 240V output, if you insist on full operation: a 240V tub's 5,500W heater plus its pumps runs about 7,000 watts. The sane outage plan is much smaller: run only the circulation pump for freeze protection (about 1,500W at 120V on many tubs) and let the water coast; a covered tub holds heat for a day or two.
Wattage by type
| Hot tub type | Running | Starting |
|---|---|---|
| Freeze-protect: circ pump only | 300 to 1,500 W | 600 to 3,000 W |
| 120V plug-and-play tub (heater + pump) | 1,500 W | 3,000 W |
| 240V tub, pumps only, heater off | 1,500 to 3,000 W | 3,000 to 6,000 W |
| 240V tub, heater + pump (planning number) | 7,000 W | 8,500 W |
What it takes with company
Same engine as the wattage picker: running total plus the single biggest start spike, then the smallest class that carries it with 20% headroom.
| Load list | Running | Peak | Buy |
|---|---|---|---|
| 240V tub, everything on | 7,000 W | 8,500 W | 9,500W portable |
| Pumps only, heater locked out | 2,000 W | 4,000 W | 3,500W portable |
| Freeze protection + the house basics | 3,200 W | 4,750 W | 5,000W portable |
The details that change the answer
Heating water with a portable generator is the most expensive heat in this catalog: the 5.5kW heater plus a pump loads even a 9,500W unit past its comfort zone, burns roughly a gallon and a half of gas an hour doing it, and raises the water a few degrees for the trouble. If the tub must truly run during outages, that's a load for the standby-generator conversation, not the portable aisle.
What a portable does brilliantly is keep the tub alive. The failure mode that costs four figures is freezing: water in the pumps, heater tube, and plumbing splits things when it hardens. Freeze protection needs only circulation, and circulation is a 1,500W-class load that shares a 5,000W portable with the whole storm-basics list. Most 240V tubs will run their circ pump if you power just that circuit; plug-and-play 120V tubs make it even simpler. A covered, full tub also buys a lot of time passively, 24 to 48 hours before the water even approaches risk in most climates.
Questions people ask
Can a generator run a hot tub heater?
A 240V tub heater plus pump wants about 7,000 running watts, a 9,500W-class portable with an L14-30 outlet and an electrician-wired inlet, since tubs are hardwired with a GFCI disconnect. It works; it also burns more than a gallon of gas per hour. For outage purposes almost everyone is better served running pumps only and keeping the cover on.
How do I keep a hot tub from freezing in a power outage?
Circulation, not heat. Moving water resists freezing, and the pump’s own waste heat helps; 1,500W or so covers it on most tubs. Under 24 hours with a good cover, do nothing. For multi-day cold-snap outages with no generator at all, drain the tub per the manual; a drained tub is annoyed, a frozen one is totaled.