OK, blood. I'll try to describe it more. Keep in mind that I didn't design or build this thing. I've had it explained to me a few times though.
I don't think the tankless water heater was 1500 bucks. 1500 is the total cost with the circuitry stuff also.
First, the tankless water heater was made for natural gas so they switched over to propane use. Not sure how that was done.
The tankless water heater puts out pretty much boiling water on demand. How the temp is adjusted is by how much cold water is added to it. So there is a temp sensor somewhere in the line.
For our system, the increments go by 5 for a bit, then 20. So you can have 120, 125, 130, 135, 140, then 160, 180. It might go to 200 but we have never gone that far. We use the 120° for our pressure washer and stuff like soaking bottles. We preheat our mash tun with 150° (we can't use super hot water or it will deform the plastic cooler mash tun). Now to get lets say we need 175 water for mashing we have to do a little combining. Say 4 gallons @ 180 then a gallon @ 160...or something like that. It's not that big of deal since you just open a control panel and push the arrow button up or down to change temp.
The water does have to be completely off before you can make the change though.
Overall, it takes less than 5 min to get strike water. That's including hooking up the water hose, propane hose, turning on valves, control panel, filling up water.
I can't give any details on the control panel though. The guy at the club that built it is an electrical engineer at Intel.