What is the Best Water Heater for a Spa or Hot Tub?

What Types of Spa Water Heaters are Available?

There is a wide range of spa and hot tub water heaters available on the market, the new and the traditional from wood-fired to electric heat pumps. We’ll break down how each type works and its pros and cons.

Wood-fired Water Heaters

Wood-fired water heaters are an antiquated technology, reserved for DIY and off-grid hot tubs. In their simplest form, they are a wood fire lit under a hot tub, though this has been surpassed by flow-through systems where cold water enters at the bottom of a series of heat exchange tubes and flows out the top as it is heated. The limitations of wood-fired water heaters are that they are slower than most other options, cannot heat the water as well and are much harder to regulate. Generally, a wood-fired hot tub needs to be lit several hours before intended use and then stoked and kept lit until the water comes up to temperature. This also limits the size of the hot tubs that they can be used on to smaller volume tubs.

Electric Element-type Water Heaters

Electrically powered element-type water heaters for spas are a very common option. These systems use electricity to heat an element that is submerged in water. In their most common configuration, these heaters have a slow but constant flow of water flow through them during their heating cycles, pumping in cold water from the spa and allowing the hot water to flow back out.

One of the main reasons that element-type water heaters are common is that they are relatively cheap to purchase and do not add excessively to the cost of a new spa. They are also often built into the spa, for example, spas offered by Sapphire Spas come with PowerSmart variable output water heaters integral to the spa design. This means there is no pipework leaving the spa to go to an external heater, providing for simple operation and a sleek, mess-free look. Our PowerSmart variable output water heaters can be operated in a smart mode that is compatible with home smart meters, this means that they can be programmed to do most of their heating during off-peak times when electricity is cheaper.

The variable output is important too, some electric water heaters only work at one power level and if they cannot draw enough current they shut off. When a spa is in use with all of the pumps and blowers operating, this means some models will shut down. But with a PowerSmart variable output water heater, you can be sure your spa will stay at the temperature you set it as the heaters won’t just cut out leaving you in the cold.

Gas Water Heaters

Gas water heating is an outdated option for heating your spa water. These designs are not dissimilar to on-demand domestic hot water services. It is usually necessary to set the temperature on a gas heater on the external gas unit itself as they aren't typically integrated with the spa topside control touchpad.

While they are available in Australia, gas-fired hot water heaters for spas and hot tubs are most common in the United States where propane for home heating is much more common. Gas water heaters are capable of heating your spa water slightly faster than electric options, but this ends up costing more than maintaining a stable temperature with an external electric heat & cool pump (described below).

Heat-pump Water Heaters

At the top of the list and universally recognized as the best water heating option is heat-pump solutions. You have probably already encountered a heat pump in your home, although in a domestic heating situation. ‘Heat pumps’ are colloquially known as reverse cycle air conditioners or ‘split systems’, but the operating principle is the same whether heating air or water. While heat pumps are electrically powered, they work in a very different way from an element-type heater.

Heat pumps get their name, not from the fact that water moves through them, the term ‘heat pump’ refers to the way that they transfer heat energy from one area to another. The system doesn’t actually generate any heat itself, but rather captures the ambient heat energy in the air and concentrates it into the water (in effect, ‘pumping’ the heat from one medium to another). In fact, heat pumps are so efficient at capturing the warmth and transferring it into water (or air in the case of a reverse cycle air conditioner) that for every 1.1kW of electricity used to operate them they typically deliver 5.5kW of warmth. This is why they are so energy efficient to operate, which makes their higher upfront cost appear negligible when compare to other options. As an added bonus, heat pumps can also be used in reverse, effectively sucking the excess heat out of your water when you want to cool it down on a hot summer day.

Which is Best?

As with many things, there is not a definitive ‘best’ option, it depends on your needs. If you have an off-grid cabin with a small 2-person hot tub then the ability to turn off and forget about a wood-fired tub could be ideal, though this is unlikely for most people.

As a rule, the choice will come down to one of two. The cheap up-front, but more expensive to run electric element heater. Or the more expensive to purchase, but much more efficient heat-pump style. Both can be set up to run at off-peak times when working with smart meters. Both provide a wide range of temperature control and can hold the temperature stable during use. If you have a smaller spa and you don’t use your spa very often then an element-type heater is fine. However, if you have a larger spa, use your spa frequently and/or want the ability to cool your spa down in summer, just as much as warming it in winter then a heat pump is hard to pass by.

Conclusion

If you are looking to get into a spa of your own then Sapphire Spas is the place to go. With more than 40 locations across Australia, there is a retail partner near you. We choose all of our partners and distributors with care, to make sure that they will offer you the same level of expertise and care that we do ourselves. Find your nearest Sapphire Spas retailer now or contact us to request a callback and find the perfect spa for your needs.