In this article we will look at some of the different ways that you might heat your hot tub.
Getting your hot tub to 37deg C.
Most people feel that the ideal temperature for a hot tub or spa is somewhere between 37deg C and 39deg C – which is about the same as your body core temperature.
How hard any heater will have to work to get the spa up to temperature will depend on the ambient air temperature and whether a good thermal cover is fitted. Once a spa is up to temperature it takes very little energy to keep it there especially if its well insulated.
There are basically four different possible methods of achieving that.
- An electrical heater.
- A gas heater.
- Using pump friction.
- Solar heating.
Heating your spa with an electric heater.
Using an electric spa heater is by far the most common method due to its relative simplicity.
An electrical heating element, similar to that which you would find in your emersion heater or kettle, is mounted in a tube. The pump in your spa pushes water through the tube and when the flow sensor indicates that sufficient water is passing over the element, the thermostat or spa control system turns the element on.
In an average family spa the electric heater will raise the temperature by about 5 – 6 degrees an hour, so how long your spa will take to heat up from a re-fill obviously depends on the temperature of the water going in.
Using a gas heater to heat your spa.
Gas heaters are usually only used in commercial situations or where the spa is combined with a swimming pool and the pool is gas heated.
Gas heaters generate a lot of heat and as a result they can heat a spa up very quickly. For that reason gas heated hot tubs are normally allowed to cool down when not in use rather than being maintained at temperature, as an electrical one would be.
Running costs for a gas-heated spa can be lower than for an electrical installation however the initial costs are much more. Gas heaters are much more expensive to buy and they are large units that need a fair amount of space to be housed as well as pipe work to carry the water between spa and heater.
Pump friction as a heat source.
The pump in your spa generates a certain amount of heat as it runs and if the pump housing is wrapped in tubing that the spa water runs through then it will slowly warm that water up at very little cost.
In practice the amount of heat generated is small and, because the pump needs to be running to produce the heat, it is difficult to control the temperature and balance the water chemistry at the same time.
Any heat produced by a water pump is wasted electrical energy and as such you are likely to find the pumps selected for this sort of installation are far less efficient at their primary task of moving water in the sacrifice to generate ‘waste’ heat for the water.
A solar heated spa sounds like a great idea. Unfortunately a solar thermal system, even in the best conditions, will only produce a relatively small amount of energy.
Solar thermal simply won’t lift the water temperature in your spa to the required point.
Obviously we are all keen to make as much use of renewable energy as possible and there are solar spa covers which will use the sun to gently top up the water temperature and photo voltaic cells could be used to run the spa’s pump under the right conditions.
We hope this article has been of use to you. There are many more articles on this site that will give you information on almost every aspect of your spa or hot tub.