The honest answer: it depends on how often you soak. Soak three or more times a week? Leave it on — the savings from cycling are trivial and the convenience isn’t. Soak once or twice a week? A setback between soaks saves real money. Away for a week? Turn it off. Anyone giving you a one-word answer to this question is skipping the physics, so let’s do the physics first — it takes two minutes and it settles the argument underneath every forum thread on the subject.
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The physics nobody mentions
Your hot tub loses heat to its surroundings at a rate proportional to the temperature difference between the water and the air. 104°F water in 50°F air bleeds heat fast; 80°F water in 50°F air bleeds it slowly. This is basic heat transfer, and it has an unavoidable consequence that the “always leave it on” crowd never addresses:
Turning the heater off always saves energy. Every hour the water sits cooler than your set temperature, it loses less heat than it would have at full temperature, which means less total heat to replace later. There is no thermodynamic trick where maintaining 104°F around the clock uses less energy than letting it cool and reheating. The engineers on eng-tips who’ve run the numbers are unambiguous about this.
So why does almost everyone — manufacturers included — tell you to leave it on? Because the question was never purely about physics. It’s about three practical costs that the physics doesn’t capture:
- Reheat time. An inflatable heats at roughly 2–3°F per hour. From cold to 104°F is 8–24 hours depending on starting temperature and insulation. Turning it off means planning your soaks a day ahead.
- Water quality. Heater off usually means pump off, which means no filtration and no circulation. Still, unfiltered spa water grows bacteria and biofilm fast — owners report cloudy water within days. The “savings” can evaporate into an early drain-and-refill.
- Heater cycling wear. Real but minor: heating elements and relays have finite cycle lives. Constant on/off cycling wears them marginally faster than steady operation. It’s a factor, not a deciding one.
MSpa’s official position — that it’s “kinder to your electric bill to maintain temperature than heat from scratch” — is best read as advice about convenience and water quality, not physics. And notably, Bestway’s own blog undercuts the simplistic version: their “5 Do’s & Don’ts” advises using the power-saving timer rather than running the heater pump continuously. The manufacturer disagrees with the absolutists.
The real answer: decide by soak frequency
Here’s the framework. Find your row:
Soak 3+ times a week → leave it on at temperature
You’re a daily or near-daily soaker. The energy you’d save by cycling is small — the tub barely cools between sessions — and the cost is spontaneity plus water-quality risk. Leave it at your soaking temperature, keep the cover discipline tight, and spend your efficiency effort on insulation instead (see below). This is most committed owners, and for them “leave it on” is correct — just not for the reasons usually given.
Soak 1–2 times a week → setback between soaks
This is where the money is. Drop the set temperature to around 88°F between soaks and boost it back up the morning of a soak day. The tub stays warm enough to keep water circulating and chemistry stable, but the reduced temperature difference cuts heat loss substantially during the 4–5 idle days. One careful owner (lee.org, who measured his actual consumption) found that even three days of reduced heating took that long to show up meaningfully on the bill — which tells you the savings are real but require the full idle stretch to matter. Don’t micro-manage it daily; set the setback and leave it.
Away a week or more → off entirely
Turn it off. The freeze-protection thermostat (which kicks in around 36°F on most models) still guards the plumbing in mild climates even with the heater off — it runs the pump just enough to prevent freezing. In hard-freeze climates, “off” should mean drained and stored, not just switched off; see our winter-use guide for the full decision.
The hidden bill: what “off” does to your water
The cost people forget: a tub with no circulation is a tub growing things. Without filtration, body oils, lotions, and the normal contaminant load sit stagnant. Owners who switch off for a week commonly return to cloudy water, biofilm on the shell, and a filter that needs deep-cleaning — sometimes a full drain and refill. Price that refill (water + chemicals + your time + the reheat energy) against the electricity you saved, and short off-periods often lose.
The rule of thumb: off for a day or two with circulation running is fine; off for a week with everything dead is a water-quality gamble. If your model lets you run the pump on a timer without the heater, that’s the middle path — circulation without the heating bill.
What actually moves the needle (ranked)
Forget the on/off debate for a moment. These beat it, in order of impact:
- Insulation under and on the water. An EVA foam base mat plus a floating thermal blanket attacks the two biggest heat-loss paths (ground conduction and surface evaporation). The lee.org case is instructive: about $50 of foam board insulation cut roughly 2 kWh per day — around $200 a year at $0.50/kWh. Few upgrades in this hobby pay back that fast.
- Cover discipline. Cover on whenever you’re not in it. Every minute uncovered at 104°F is money evaporating — literally. A waterlogged or ill-fitting cover undermines everything else; our covers guide covers when replacement pays for itself.
- Wind protection. Wind strips heat from the walls far faster than still air. A screen or fence on the windward side is free efficiency.
- Off-peak timing. If your electricity tariff has off-peak hours, a timer plug scheduling heating cycles overnight cuts cost without cutting comfort. This is what Bestway’s power-saving timer is for — use it.
- The on/off decision. Yes — fifth. After the four above, the residual savings from cycling are modest. Do the big things first.
The math, shown honestly
A typical inflatable runs a ~1.3 kW heater. Suppose it runs a 30% duty cycle to maintain temperature in mild weather — that’s about 0.4 kW average, or roughly 9.6 kWh per day. At $0.30/kWh, that’s about $2.90/day just to idle.
Now the setback case: dropping to 88°F between soaks might cut the duty cycle roughly in half during idle days (the exact figure depends on insulation, wind, and ambient — these are transparent assumptions, not measurements). Over 4 idle days a week, that’s on the order of $5–6/week saved — real money over a year, roughly $250–300, if your tariff and climate match the assumptions.
Don’t take our arithmetic as your bill. Plug your own rate, your own tariff structure, and your own soak pattern into the 5-year running-cost calculator — it has an on-vs-cycle scenario built for exactly this question — and see what your numbers say. Then sanity-check the annual picture in the ownership planner.
FAQ
Does turning it off damage the pump?
Cycling wear is real but minor compared to the heater element’s own lifespan. Pumps are built to cycle; what kills them is running dry, freezing, or chronic overheating — not being switched off. Don’t let wear fears override the math.
What about economy mode?
If your model has an eco or timer mode, it’s the manufacturer’s answer to this exact question — scheduled heating windows instead of continuous operation. Use it; it’s the setback strategy with a button.
I’m going on holiday for two weeks in summer. Off or on?
Off, with the chemistry balanced before you leave and the cover secured. Two weeks of idle heating for zero soaks is pure waste. Shock it when you return, test before soaking. In winter, the answer differs — see the winter-use guide.
Does it matter for hard-shell tubs?
The physics is identical; the numbers are kinder. Better insulation means lower duty cycles, which means the on/off decision matters less. This site covers inflatables, where the decision matters most.
The bottom line
The forums will keep arguing “always on” versus “always off” forever, because both camps are half right. The physics says off saves energy — always. Practicality says the savings only matter at low soak frequencies, and water quality punishes careless cycling. So: daily soaker, leave it on and insulate instead. Weekend soaker, set back between soaks. Away for a while, switch it off. That’s the whole answer, and it’s the one the simplistic takes skip.
Fold the decision into your routine via the maintenance schedule, and if winter is what prompted the question, read the winter-use guide next — cold changes every number on this page.
