Excess flow valve

I've finally installed this excess flow valve "at the appliance" (the tankless water heater)... merely to satisfy the building inspector who requested it.
It's hardly the correct size. I couldn't find one that's right. Nobody sells it. I don't think anybody makes it for such a small tankless water heater. The Bosch 1600H draws a maximum of 117 KBTU/hr through a 3/4" NPT pipe. The mismatch is either the shutoff capacity or the physical pipe size.

An excess flow valve is a device designed to shut off the flow of natural gas automatically in the event the gas service line is broken. It's best when rated to shut flow approximately 50% greater than the anticipated normal flow.

At a cost of $95, this unit closes at 300 KBTU/hr -- but it's 3/4" pipe.