Hot water in bathrooms

Had an odd situation today. Inspected an old 1950 house converted to a hair salon now being sold to my client for an office. It had a conventional 40 gallon hot water tank used for the hair washing stations. The only bathroom is a 1/2 bath and due to a tight crawlspace someone installed a small BOSCH tankless hot water heater in the wall just for the bathroom sink. The water flow at the sink appeared to be low and the hot water never exceeded 85-87 degrees with the hot water faucet fully open. First thought was the tankless heater was not functioning properly. Agents bickering back and forth as usual so I went back after a plumber said the water heater was functional. I got the model number and it turns out this BOSCH tankless water heater comes in 9 different versions. So happens this is the only 110-120 volt heater all the others are listed as 208 to 240 volt system with different amp ratings. The chart listed the heater I was dealing with was capable of raising the water temperature 28 degrees at a flow rate of 0.75 gallons per minute. Checking the IRC there is no minimum temperature, however the IRC’s definition of hot water states it must be at least 110 degrees. The IRC also states the minimum, flow rate for a bathroom sink is 0.8 gallons per minute. I went to my kitchen sink at home with a quart measuring cup and calculated the flowrate based on the flow rate I saw during the inspection. Turns out the IRC 0.8 gallons per minute minimum is not very much. Putting all this information together we have a tankless water heater that is producing the correct amount of heat for the sink’s flow rate based on 60 degree city water. However since the IRC definition for hot water is 110 degrees this bathroom basically has no hot water. It’s out of my hands, I am letting the agents fight it out.


sounds like that machine is doing what it was designed to do…apparently they picked the wrong machine…


Good info, thanks for sharing.