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California Energy Commission (CEC)

The maximum energy consumption in standby use was set by the CEC to be:

Q = 5 W x V^2/3

with V = volume in US gallons at 15.6°C (60F) ambient and 38.9°C (102F) spa water temperature.

A mid sized spa holding 355 US gallons or 1344 liters of water (such as our test spa) would qualify with a standby energy consumption of max. 250 W!

According to this equation spa mfg might be tempted to quote higher volumes than the existing spa shell volume in order to pass this energy consumption criteria.

For German average ambient temperature of 8°C the standby energy consumption can be linearly interpolated to be about 337 W (with a reasonable accuracy).

Several tests on energy consumption have been carried out under different test conditions. Please find below some of our test findings:

HotSpring presents own tested energy calculations for their SOVEREIGN model on their web site as well as an online energy calculator.

The SOVEREIGN is quoted with an energy consumption of 186 kWh/m at 60°F (complies with CEC) and 220 kWh/m at 45°F (= 8°C, Casper or Germany) average ambient temperature including 6 days a week usage.

For CEC conditions the 186 kWh/m represent a wattage of 258 W, however, including spa usage! This figure demonstrates that the SOVEREIGN's energy efficiency is significantly better than the CEC standard!

For estimation the spa's standby energy you may want to deduct approx 3 kWh¹⁾ per spa usage which brings it down to approx. 154 W standby wattage.

¹⁾ estimated heat loss when using the spa for 30 minutes with operating jet pump for 15 min.

Alberta Research Council Inc carried out thermal performance tests for eight different spa models in 2005. All spas were examined under steady state conditions at spa temperatures of approx 40°C and ambient temperatures of  +20°C (room temperature) and -13°C (freezer temperature).

The best energy results showed the models from HotSpring (Vanguard) and ArcticSpas (Kodiak). The Vanguard required 135 at W and 410 W for ambient temperatures of +20°C and -13°C respectively. Other spa models consumed up to three times the energy and even more!

The complete test report can be downloaded at the ArcticSpas' website.

These figures suggest a spa specific efficiency rating or U-value for the HS Vanguard between 7.1 W/K (at 21°C) and 7.6 W/K (at -13°C).

Accounting for an average annual temperature in Germany of 8°C the best energy saving spa models calculate an average heat loss of 226 W¹⁾, hence, 5.4 kWh/d or 163 kWh/m or 1980 kWh/a in standby mode. Multiplied with the updated power rate²⁾ gives an estimation of the standby costs.

¹⁾ calculated from 7.3 W/k x (39°C - 8°C)

²⁾ energy rate currently 0.22 €/kWh in Germany

ArcticSpas recently published an insulation comparison between their spa and a competitor spa. Their published thermographic images show the spas' heat loss.

It has to be noted that the comparing pictures seem to be taken with at least two different camera settings and also showing a different color scheme. Important ambient and spa water temperatures are not stated. Therefore, the two different thermo pics do not allow a thermal comparison of the two spas.

To be noted: The company was located in Northern Ireland and went out of business recently (in case you wonder that the above stated link is offline).

Armstark Germany still advertises for their SundanceSpas with an energy test report performed by the TUV Süd (Germany). The report states that the energy data presented are based on a rough calculation!

It also has to be noted that

• Energy rates of 0.14 €/kWh are still applied for the calculation of the spa's energy costs while the average rate in 2008 is currently 0.20 €/kWh (in Germany)!
• The test model Caprio has been out of production since 2006, however, the test data was produced in  August 2006.
• Whereas the Caprio came with a 88 W circulation pump, the latest models employ a 24/7 170 W circulation pump which alone consumes 4.1 kWh/d or 0.82 €/d just for circulating the water!
• Test temperatures were set to unusual values, such as an ambient temperature of 10°C and a spa temperature of 37°C only! (according to CEC standards spa temperature should be at 39°C)
• Spa usage was restricted to only 30 min, 3 times/wk, with jet pump on for 20 min.

Although these test pattern seems to be out of a standard, HotSpring contracted the German TUV Süd to test their models Jetsetter and Aria under the exact same test conditions.

The spa comparison between HotSpring and SundenceSpas can be found at www.demodomo.de/spa-vergleich.htm.

Sauna Pool and Ambiente published in 03/2005 a test of eight spa models. The best energy consumption again showed a HotSpring spa (here Envoy) with an steady state energy consumption of 4.4 kWh/day at 6.3°C ambient and 37°C water temperature.

From these figures a spa specific efficiency or "U-value "of 6.0 W/K can be derived for the HS Envoy model.

The data stated above are taken from published reports and sources and do not necessarily reflect our own test results!