Natural gas hot tub vs electric


Looking for a hot tub but not sure which heating system to choose? With modern improvements in both natural gas and electric heating systems, it can be hard to work out which has the edge.

The fact is it's not as simple as one being better than the other. Gas heaters and their electric counterparts have very distinct characteristics and are suitable for different types of hot tubs as a result.

Read on for a run-down on the pros and cons of each type of hot tub heater. You'll soon be able to tell whether an electric or gas-heated hot tub is the right choice for you.



Hot Tub Heaters Explained


Gas Heaters

Although there are two different gases used in gas hot tub heaters, propane and natural gas (a mix of alkanes but primarily methane), both operate on the same principle. Propane gas tends to be slightly more expensive but produces around twice the heat energy per unit volume (measured in British Thermal Units) as natural gas. This means you use less gas overall and gas from a propane tank generally work

Gas-fired heaters operate by circulating the water over a gas flame and back into the hot tub. 

Gas Heaters

Temperature sensors in the hot tub cut off the gas when the water has reached the desired temperature and reactivates the gas heating element using spark ignition when the water temperature falls back out of range.

Gas spa heaters are always mounted outside the spa cabinet due to the requirements for a constant supply of fresh air and the safe removal of carbon monoxide exhaust fumes.


Electric Heaters

Electric Heaters

Electric hot tub heaters use a heating element with high electrical resistance to transfer thermal energy to the hot tub water. They are also often called flow-thru heaters, as the water flows through a stainless steel tube containing the electric heating element. In addition to temperature sensors to control the heating element, pressure switches ensure a steady water flow.

Being smaller than gas spa heaters and not relying on combustion, electric heating systems can be installed inside the cabinet on most hot tubs. The relative simplicity of electric spa heaters also offers some benefits in terms of reduced maintenance costs.



Factors to Consider


Heating Power

Gas spa heaters have an advantage over electric heaters in terms of speed and heat output (BTUs). For anyone who needs quick heating, or are trying to operate especially large hot tubs (over 700 gallons) or swim spas, gas heat will give the best heat gain.

Even an 11kW electric heater can take hours to increase the overall hot tub water temperature by a few degrees in cold weather, whereas a gas hot tub can achieve the same effect in minutes.

This is also important for open-air spas and wooden hot tubs which tend to have poor insulation. It's much harder to keep wooden spas and other models which suffer from significant heat loss up to temperature using electric spa heaters than with propane gas.

However, for designs that don't suffer from so much heat loss (smaller portable spas with good insulating covers or inground spas), the energy efficiency of an electric hot tub heater is probably more important than the higher output from gas heat.


Initial Cost

Electric spa heaters cost significantly less to buy than gas heaters, which can exceed $1000 compared to only $100-300 for an electric heater. The relatively low initial cost of an electric hot tub heater is also compounded by potential differences in installation cost.

Getting an underground gas line connected from the hot tub heater to either a mains natural gas meter or a tank at another part of the property can be very expensive, depending on the distance involved. If you're operating your gas heater using a natural gas or propane tank kept near the spa, a flexible gas line may suffice. However, you should still get a certified gas contractor to check the gas line is secure and the heater is properly installed.


Operating Costs

The relative operating costs of gas or electric spa heaters depend on your location. The cost of gas has come down over the years but, for customers living somewhere relatively warm e.g. Southern California, and using either in-ground spas or well-insulated portable hot tubs, the energy efficiency of electric heat is still likely to work out cheaper.

In colder climates requiring more heating, or for less efficient hot tubs, the thermal efficiency of gas hot tub heaters will mean they don't have to be run for as long. This could mean lower overall running costs.

In addition, some areas simply have higher electricity costs than others, which can tip the balance in favor of gas heaters. It's important to check your electricity tariff, as customers paying over $0.25/kW often find the saving from using gas outweighs the initial cost of buying and installing a gas heater.



Potential Hazards


Gas Hot Tub Heaters

Whether attached to a mains gas line or a propane tank, you're still dealing with highly flammable gas.

Gas leaks, whilst very rare in professionally installed systems, can be especially hazardous since any spark or naked flame nearby can cause a gas explosion. 

In the case of wooden hot tubs, for which gas heaters are the most popular choice, a fire resulting from a gas leak can potentially ignite the hot tub frame itself.

Gas Hot Tub Heaters

The more insidious danger resulting from a gas heater is the carbon monoxide exhaust emissions. Carbon monoxide is odorless and colorless, but highly toxic. Proper installation and inspection by a certified gas contractor will help to ensure the exhaust system is suitably routed and ventilated to prevent your gas spa heater from posing a significant carbon monoxide risk.


Electric Spa Heaters

Although electric spa heaters don't use an open flame or flammable materials, there is a risk of electric shock if the system is damaged or misused. As there is water involved and most hot tubs and swim spas operate on a high-powered 220V system, the consequences of such a shock can be serious.

However, most modern electric hot tubs are fitted with a Ground Circuit Fault Interruptor (GCFI) which will cut the power in a few milliseconds if a potentially hazardous fault is detected, protecting the user. If your portable spa is supplied without a GCFI, the electrician who installs the hot tub will be able to fit one at the point of connection.



Final Thoughts

For the majority of users, the lower purchase and installation cost, energy efficiency, and low maintenance requirements of an electric hot tub make this option preferable to using a gas spa heater.

That said, if you need the extra BTUs offered by gas heat for any of the reasons mentioned in this article (large hot tubs, poor insulation, or cold climate), the added power of a gas heater will allow you to get the best use out of your hot tub.

If you're still thinking about whether to buy a gas or electric hot tub, why not get some information on the specifications and pricing of hot tub brands in your area. Filling out the form below allows your preferences to be passed on to the most reputable local dealers, so you'll receive their very best quotes regardless of whether the model you choose features a gas or electric heater.



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About The Author

Meredith Kiley

Full-time staff writer at wyllz.com and stay-at-home mom.