09/10/2026
Saw this in class today over here at Rinnai’s home office.
What you’re looking at is a portion of a heat exchanger inside of a tankless water heater. Water passes through these “tubes” and is heated as it does so.
Notice the white build up? This is scale, which develops overtime and is found in the water. The openings on the left have been cleaned so that you can see what size they should be compared to what the scale has restricted it down to.
This amount of scale formed within only 2 years! When it builds up like this, it impacts both the flow rate the tankless unit is able to handle as well as the efficiency at which it operates.
Granted, this specific heat exchanger came off of a unit in Texas, where the water tends to be much harder than what we have locally. While this is a useful visual example of why manufactures (and plumbers) recommend you routinely have your heaters descaled, I’m sharing this because I thought it was fascinating to see. I wouldn’t look at this and be fearful that your 2 old tankless is built up to this magnitude with our local water.
By the way, scale impacts tank style heaters as well. It isn’t something which only affects tankless systems.
