18-29-503.1.1 Shut-off valves
Shutoff valves for water heaters or heated water storage tanks may be installed on the inlet side only.
I inspect in around 80 separate communities in Lake and Cook counties (northern Illinois), most if not all prohibit a valve on the outlet side of a WH.
Chicago AHJ don't count. They're in a world all their own when it comes to codes.
2 wks ago I installed a 120 gal HW storage tank, valved both lines. Today I wrapped up a bank project, again I used 2 valves. Both projects passed inspections and each job was in a different state.
About the only time I see or use one valve is on residential work- trying to save a buck on materials.
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