Have you considered a larger water heater, then 2 in tandem? Seems like 2 would take up too much space. Another option is indirect storage tank if you have a hot water boiler. It taps off your boiler and is useful for large demand such as your spa. www.crownboiler.com will give you some insight.

Well, this is a brand new house, the water heater has been turned on for 2 weeks and I am just thinking that for $200, (cost of another LP Gas water heater) I couldn't go wrong. versus removing it and having one I can't use. Space is no problem.

Some questions I have are: Can I use the same flue? just Y in a new line. Parallel or series?

Thanks

I have two LP 40 Gal water heaters on one flue you want to make sure you have at least a 5 " flue though.
Mine both have a shut off valve on the Hot & Cold side in case one has trouble I still have hot water. Personaly I would not run one water heater into the next even though tat is possible but run them into the main hot water line on there own (I think this is referred to Parallel. If you have the room, Go do it. I love having 80 Gal of Hot water I havent run out yet on a family of 5 with a supersize tub, 2-showers, dishwasher and wash machine. have a Merry Christmas!
Mike<><

Thanks