A few weeks ago I was a the old Green flash brewery in Vista CA, and noticed two large commercial tankless water heaters on the wall. I did a little reading on pro-brewer and saw that there are a few small breweries that use two tankless water heater, or a tank water heater and a tankless heater to reach their strike and sparge temps.
Here at my house I use my tankless heater to fill my HLT with water at its max output 140. Now that I am looking to get my 20gallon system up and running, I have been thinking of trying to find another tankless water heater to install in line to take the 140º out put of the first and raise it to 170-180 to handle the mash and strike temp right away, and avoid the time to heat the water in the HLT.
Now, I think most household tankless heaters have a temperature sensor that limits their max output. As well new tankless heaters can be quite expensive. I have been looking on CL and ebay and have seen some as low as 150, so that would be do able.
I want to put this out to the HBT group to see if any one has experience with doing this or just enough knowledge of tankless heaters to let me know if it can be done with a residential tankless heater. BTW I have access to NG and 220VAC where my brewery is set up.