How To Pick the Right Tankless Water Heater

This video started off as a review of the RETEX-13 tankless water heater, but it became a buying guide. Turns out that 220V tankless water heaters add about one degree Fahrenheit when water flows through at 1.5 gallons per minute.

The simple formula for determining which to buy based on amps is desired shower temperature minus groundwater temperature on coldest winter day. In my case, the bride wants 110°F showers and the coldest winter groundwater in my town is 60°F, so I need a 50amp solution or better.

I had unnaturally good results with EcoSmart 8 tankless water heaters in the past, but it turns out that I was artificially restricting the flow by using 3/8" hoses under the kitchen sink. The temperature rise is inversely proportional to the flow rate and my EcoSmart 8 tankless water heaters were adding 50°F instead of the realistic 34°F based on wattage.

The takeaway for me is to use 11kw or 13kw tankless water heaters going forward despite the success of the EcoSmart 8 in the past. The Rheem, EEMAX and EcoSmart 11kw and 13kw tankless water heaters cost about the same as the 8kw versions and eliminate the risk of callbacks based on too little temperature rise.