1. Electricity Costs: 

The main expense is electricity, which is used to heat the water and power the pumps and jets.

The average monthly cost of electricity for a hot tub can range from £10 to £40, but can also range from £40 to £100 per month, if you live in a colder area where the heater needs to work harder.

The difference is mainly due to the quality and integrity of the hot tub insualtion.

Always make sure that you get running cost quotes in writing from the seller that are specific to your intended usage (where you're going to install your hot tub and when and how often you're going to use your hot tub).

2. Frequency and Duration of Use:

Frequent use can increase costs since maintaining the water temperature requires more energy.

Conversely, consistent moderate use can be more economical due to the reduced need for reheating. 

When in the hot tub water is around 38°C (100–102°F), with the cover removed, and if the ambient air temperature is below 12°C (53°F), the temperature of the hot tub water will reduce while in use, and therfore require energy to reheat. 

3. Temperature Settings:

Running the hot tub with higher temperatures will increase heating costs. Keeping the hot tub at a slightly lower temperature - for example: 38°C (100°F)  instead of 40°C (100°F) can save energy.

Advanced control panels, and customised fitration, circulation and heating setting will also help reduce energy costs. Some hot tub controls can be controlled via a smart phone.

4. Insulation and Covers:

Well-insulated hot tubs and effective covers can dramatically reduce heat loss when not in use. Minimising heat loss translates directly into energy cost savings.

Effective hot tub insualtion can reduce your running costs to around £10 per week through the winter months - this test was carried out for 28 days through temperatures ranging from 10C to 15C (50F-59F) on a hot tub with Triple Insulation (which is a combination of Partial Foam Insulation on the shell, Reflective Insulation on the inside of the cabinet and Thermal Wrap) and with a 5 inch vinyl cover.

Note: weekly hot tub running costs can be as low as £5 per week, when ambient outdoor temperatures are in excess of 23C (77F).

5. Water Care and General Mainenance:

You'll need chemicals to keep the water clean and balanced, including chlorine, bromine, and pH adjusters, which can add to the cost.

Better hot tubs have advanced systems that reduce the amount of time and money that you will have to spend on maintaining clean hot tub water.

Regular maintenance, such as replacing filters and maintaining the cover, ensures energy efficiency but also comes with a cost.