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SioGreen Tankless Water Heaters in Cold Climates?
Northeast Wisconsin Case Study - April 2023
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We recently completed a test installation in Northeast Wisconsin to determine if the SIO 18 Pro/Pro Flex would perform adequately in a colder climate. Here are the results:

Situation: The customer frequently would run out of hot water when the 5 family members (Mom and Dad, 2 teenage daughters and 1 young son) would take back-to-back showers after camping weekends. He has a 50 gallon gas tank heater and would add cold water to the hot water to extend the volume of heated water.

Solution: We recommended a test to determine if we could supply enough preheated water to the gas tank heater to provide a continuous flow of hot water. A SIO 18 Pro was installed to boost the temperature of the water entering the gas tank water heater rather than cold water requiring recovery time.

Results: The incoming water temperature was approximately 50 degrees. (The average winter ground water temp in Wisconsin is 45 degrees) The tank heater was set at 115 – 120 degrees. The SIO 18 Pro was also set at 115 degrees... a 65 degree rise.

Cold Weater Hot Water Boost
Cold Water Inlet Temp

Test 1: A single shower with a 1.5 GPM low flow shower head was turned on and ran for 45 minutes. (67.5 Gallons) The water continued to flow at 104 degrees with some cold water added to the flow to achieve a comfortable temperature. In this test, the gas tank heater did come on occasionally to maintain the temperature. There was no noticeable reduction in the flow rate.

Test 2: The temperature on the SIO 18 Pro was increased to 120 degrees and the test was run again. This time the shower ran for 60 minutes (90 Gallons) and the gas heater never came on. Also, the gas heater did not go into recovery mode to reheat any water.   

Test 3: Two showers were turned on simultaneously and run for 45 minutes. (135 Gallons) There was no noticeable reduction in flow and the hot water temperature remained at 104 degrees. Again, the gas heater never came on during the test. Click here and expand to full screen to see the test video.















Conclusion: The SIO 18 Pro performed without any issues. The goal was to provide a continuous flow of hot water for extended periods and mitigating the energy costs by eliminating the gas heater's recovery time. (In all cases, the amount of water used exceeded the capacity of the tank and would have required additional time to recover.) While there may still be minimal gas usage in standby mode, even that can be mitigated with a thermostatically controlled recirculation pump.


These goals were successfully achieved and demonstrated the viability of the SIO 18 Pro as a booster unit to existing tank heaters, providing a continuous flow of hot water for extended periods at a reduced operating cost in colder climates. The SIO 18 Pro only runs when hot water is in demand. This may not qualify as a scientific test but the customer is thrilled, and we all know who pays the bills.

In addition, these units are MAINTENANCE FREE…no scaling and no annual flush.

Actual Shower Temp Boosted
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