I agree with what has been said about parallel however I think series may be more efficient as far as energy usage. I piped mine in series manly because the house only had one heater when I bought it and I added the second and it was easier to pipe that way. I put the new heater in front of the 10 year old heater so the new one is doing most of the work.
10 years or older time to change. Playin with the lottery


at for not having enough hot water
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