Condensing Tankless Water Heater Maximum Exhaust Temperature

Let's crank the heater up to 11 and see how hot the exhaust stack gets.

Had the bathroom shower and kitchen sink on full flow plus the utility sink. Water temperature set to the maximum 140°F − 60°C and had the tankless heater limiting the water flow a bit to maintain the set output temperature.

With the inlet water temperature at 73°F − 23°C and water flow at a minimum, this should be the worst case for exhaust gas temperature. This is because the exhaust gas is cooled by the incoming cold water flow. Had I rum up to the rate 6.6 GPM flow rate (with a lower outlet temperature) or had tested in the winter with colder water temperature, the exhaust gas would be cooled even more. So the 132°F − 55.5°C reading should be as hot as this would ever get and it's safely under the 140°F − 60°C temperature rating of the PVC venting material. I did reach up and touch the vent pipe. It was warm to the touch, but neither it nor the steel fitting it plugged into were too hot to touch.

More to come...
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Intro/Outro:
Louisiana Fairytale by Austin Rogers
https://web.archive.org/web/20170402222425/http://drfiddle.com/show_tune.php?id=94