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So, what’s your Flow Rate?

Flow Rate Fallacy

This seems to be the question everyone asks, but for the most part, projected flow rates are somewhat meaningless and not a legitimate measure for comparison. Let me explain.

Flow rates have become one of the industry standards for comparing tankless water heaters. Every manufacturer touts their flow rates without regard to the variables you run into in actual installations, so it becomes more of a marketing exercise. It may be a starting point, but hardly the final analysis.

First of all, these are projected flow rates for a brand-new unit out of the box and tested under controlled conditions. What are the baseline criteria for these tests? Are all manufacturers using the same testing methods? As an example, what is the water pressure, inlet water temperature and plumbing specs?

I will give them the benefit of the doubt and assume all things are equal and there is a baseline test criterion.

But then there is reality:

  • Electric tankless water heaters, aside from SioGreen, use electrical resistance metal heating elements which will attract and form lime and mineral scale to one degree or another.

  • Mineral scale insulates the heating element requiring more electricity to heat the water to the same temperature or reduces the flow to maintain temperature.

  • Depending on the hardness of the water supply, water heaters can lose up to 50% of their efficiency in 6-12 months.

  • From day one, the efficiency of the water heater begins to degrade due to mineral scaling.

  • If not maintained, the life of the heating elements can be cut in half.

  • Every manufacturer recommends descaling and flushing these units at least once a year under their regular maintenance schedule. In hard water conditions, this process should be done every 6 months.

  • Every plumber knows this, but only a few tell their customers.

What real value does the initial flow rate test have if you don’t consider what is actually happening inside the heater? Nobody monitors the actual flow rate periodically to track it. The only meaningful comparison is not the initial flow rate claim, but rather the cost to maintain that flow rate over the long term.


“Maintenance Free” is not just a SioGreen slogan. If you want a comparison that has actual value, we should examine the long-term flow rates in a side by side comparison after 1 year…2 years…3 years…without maintenance on either unit! How about 10 years?


For any of the competition's tankless water heaters to maintain the original flow rates, the units must be maintained according to the recommended maintenance schedule. The estimated cost to descale and flush a typical electric tankless water heater is $200.00/yr... every year!


The cost to maintain the performance of the SioGreen Tankless Water Heater is “$0.00”!

Want proof? We guarantee the SioGreen heat exchanger for 10 years. No other company in the world offers a warranty of any kind on their metal heating elements. They vaguely refer to a warranty on the tubes that encase the heating element, but not the element itself.

Maintenance Free Operation - Here's Proof

Not a projection...actual performance.


This heating element was removed for inspection from an early prototype unit installed in 2010 during the R&D period. This array ran 9 hours/day, 365 days/year for over 7 ½ years in a nail salon with no scale, no maintenance, and no loss of efficiency. The only minor issue was a slight discoloration on one tube from insulation. To put that in perspective…

That is 24,638 hours... …or equivalent to over 22 years of use in a typical household.


The new SioGreen Heat Exchangers have been upgraded and improved since 2010 and the SIO 18 Pro Flex will likely be the last water heater the homeowner will ever buy, considering the average homeowner stays in their home for less than 13 years.

So long story short, the current flow rate comparison between all the other electric tankless water heaters using the outdated metal heating element technology is only valid for those outdated water heaters. It is also just a snapshot in time with no long-term accuracy. SioGreen's flow rate projections are good for today and the next 10! So, are the typical industry flow rates a fair comparison?

With SioGreen, there is no comparison!

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