How to Work Out What Your Hot Tub Costs to Run on Your Own Tariff
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Your hot tub’s running cost comes down to a simple equation: kilowatt-hours per day equals heater wattage multiplied by daily run hours divided by 1,000; daily cost equals kWh multiplied by your unit rate. Most guides skip the runtime measurement, leaving you with unreliable averages. This article shows how to measure it properly.
The formula works for any tariff. You need your heater’s power rating in kilowatts, your electricity unit rate, and how many hours your heater actually runs daily.
Why Running Costs Vary So Much
Two identical-looking tubs can produce electricity bills that are twice as far apart. The sticker price tells you almost nothing about running costs.
Three factors interact to determine what you’ll pay:
Heater power — measured in kilowatts (kW). A more powerful heater doesn’t always mean better performance—it can indicate the tub loses heat quickly and needs extra power to compensate.
Insulation quality — this creates the biggest cost differences. A well-insulated acrylic tub with a rigid shell retains heat efficiently. An inflatable with soft-sided walls and a basic cover loses heat much faster, potentially doubling your daily running cost in colder months.
Weather and usage — ambient temperature and how often you use the tub significantly impact runtime. A cold October night forces the heater to work harder than a mild July evening. Frequent lid opening, leaving the cover off overnight, or running jets without heat all increase runtime.
Most cost guides overlook these variables, giving you numbers that don’t match your situation.
The Honest Calculation Method
You’ll need three numbers from your specific setup:
- Your heater’s power rating in kilowatts (kW) — check the manufacturer’s spec sheet or unit label
- Your electricity unit rate in pence per kilowatt-hour (p/kWh) — from your latest bill or the Ofgem price cap if you’re on a standard tariff
- Your heater’s daily runtime in hours — this is the critical variable that varies by season and conditions
The calculation is straightforward:
Daily cost = Heater kW × Runtime hours × Unit rate
Example: a 1.5 kW heater running 4 hours daily at 30p/kWh costs 1.5 × 4 × 0.30 = £1.80 per day. Monthly, that’s approximately £54. But runtime changes with weather—it could be 8 hours in winter or just 2 in summer.
The safest way to measure runtime is using your smart meter’s display. Note readings at the same time daily for a week of normal use, then compare with a week when the tub is off. The difference divided by days and heater rating gives your average runtime. Don’t use plug-in energy monitors unless your manual specifically allows them—many inflatable tub makers require direct wall socket connection for safety.
Real-World Cost Estimates
These figures illustrate potential ranges under specific conditions—your actual costs will differ based on your setup and usage.
- Standard insulated hot tub (used 2–4 times weekly, 38°C, good cover): approximately £2.20–£3 daily
- Highly efficient models: around £1.00–£1.30 daily at 27.69p/kWh—adjust for your tariff
- Inflatable hot tub: can reach £5 daily in colder months due to less effective insulation
- Lay-Z-Spa models: £0.60–£1.70 daily, varying significantly by model and season
- Lay-Z-Spa ThermaCore with a thermal cover (paid link): as low as 50p daily according to customer reports, but only with good cover condition and mild weather
The wide range shows why generic monthly figures are unreliable—your specific situation determines where you fall within it.
How Design Choices Impact Running Costs
If you’re buying new or looking to reduce current costs, understanding these factors matters.
Heater power alone can be misleading. A high-kilowatt rating sometimes indicates poor insulation—the tub loses heat quickly, requiring more power to maintain temperature. You pay for this inefficiency every time the heater runs.
Insulation quality is the real cost-saver. Rigid acrylic shells with proper insulation hold heat far better than inflatable PVC walls. The cover is equally important—a worn, compressed, or ill-fitting cover significantly increases heat loss.
Practical steps to reduce costs:
- Check cover condition first—compressed foam or poor seals are major heat leaks
- Use a thermal blanket if your tub supports one—adds insulation without replacing the cover
- Keep filters clean—clogged filters reduce water flow, making the heater work harder
- Maintain proper water level—exposed heating elements work less efficiently
Proper maintenance can make a substantial difference in runtime between seasons, potentially halving your costs in warmer months.
Common Questions About Running Costs
How much does season affect costs?
Running costs are significantly lower in summer. Warmer ambient temperatures mean the heater works less to maintain temperature. The runtime difference between summer and winter can be substantial.
Should I get a special electricity tariff?
While Economy 7 and some smart tariffs offer lower night rates, most hot tub heaters run throughout the day to maintain temperature. Unless you can schedule heating exclusively during off-peak hours, the savings may be limited.
Can I reduce costs without buying a new tub?
Yes—several low-cost measures help. Ensuring a tight-fitting cover, using a thermal blanket, keeping filters clean, and minimizing lid-open time can all reduce runtime. These habits cost little but deliver noticeable savings.
Cost Comparison Table
| Hot Tub Type | Daily Cost Range | Key Factor |
|---|---|---|
| Standard Insulated | £2.20–£3.00 | Rigid shell and foam insulation |
| Most Efficient Models | £1.00–£1.30 | High insulation quality |
| Inflatable | Up to £5.00 | Soft-sided walls and cover condition |
| Lay-Z-Spa (Standard) | £0.60–£1.70 | Variable by model and season |
| Lay-Z-Spa ThermaCore | As low as £0.50 | thermal cover (paid link) and mild weather |
Figures assume a unit rate of 27.69p/kWh and usage of 2–4 times weekly at 38°C.
Applying Your Calculation
The numbers you calculate using this method become the foundation for bigger decisions. Specifically, they’re the essential input for assessing whether keeping your tub running through winter makes financial sense. Our winter running guide shows exactly how to apply your personalised cost figures to that seasonal decision.
Beyond electricity, remember that chemicals, filter replacements, and water changes contribute to total ownership costs. Proper water care reduces frequency of drains and refills, trimming overall expenses.
Get the free hot tub water checklist to manage these additional costs effectively.
Further Reading
Is It Worth Running an Inflatable Hot Tub Through a UK Winter? applies your calculated running costs to the seasonal decision.
Sources & Further Reading
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Note: The figures provided are estimates based on typical usage. Your actual costs will vary depending on your specific setup, local conditions, and usage patterns.