Will plumbing a hot water heater backwards affect its efficiency?

I have a 30 gallon, natural gas water heater and seem to run out of hot water rather quickly. Taking a shower the water starts to go cold after only about 10 minutes. After looking at the water heater one day i noticed that the pipes are switched around. The cold water goes in where the hot water should come out,... show more I have a 30 gallon, natural gas water heater and seem to run out of hot water rather quickly. Taking a shower the water starts to go cold after only about 10 minutes. After looking at the water heater one day i noticed that the pipes are switched around. The cold water goes in where the hot water should come out, and vice versa. I recently purchased this home, so this was done before i bought the house. The water heater has the paperwork and sales reciept with it and it is only 5years old. So i don't think that it would be filled up with hard water and lime deposits already.
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