Water Heater supply and return reversed

Can anybody tell me definitively what is wrong with plumbing a water heater backwards (cold supply into hot outlet and hot outlet coming out of cold supply port)? I’ve only seen it a couple times. In both cases the sellers had no idea it was wrong and said they had no problems with their hot water. I still wrote it up as a major concern that should be remedied. But why exactly is it so bad?


It will work but usually operates at a decreased efficiency (40 gal. will work like a 20-30 gal)
Personally, I wouldn’t classify that as a major concern.


Thanks for the reply. I told my clients (hope I was right) that the internal piping took the cold water supply down to the bottom of the tank and the hot return came off the top (since heat rises); thus, when piped backwards, there would be less hot water, it would take longer to heat the water, and the energy consumption ($$$gas bill$$$) would be considerably more than the manufacturer intended.

BTW, I’m gonna be in Surprise for the next 10 months for Operation Jump Start. If you need any weekend help with inspections, please gimmee a call.

Thanks again,
(406) 468-4095

anytime. yes, you were correct about the way the hot/cold water mix when the lines are reversed. thanks for the offer of support.