In anticipation of joining two families that will total 4 teenagers and two working professionals, we are renovating our 1 1/2 story cape and will be adding at least one full bath and a new laundry room as well as bedrooms. Currently we have a 2 year old 50 gallon natural gas water heater is not providing enough hot water for our needs on busy mornings when 6 people have to shower in a short period of time. So, I would like to add a second water heater. For various reasons I would prefer not to install at tankless heater in the new bathroom. There is no plan for a hot tub at this time. My question is: if I add a second 50 gallon heater, should they be connected in series, or in parallel? If I add a new, smaller heater, should they definitely be in series. If in parallel, should it be reverse return?

Don't worry, a plumbing design consultant and plumber will be involved, but I want to be knowledgable about the situation.