Hey Dana,
Not sure I fully understand that setup but the 50Gal didn't have much issue unless multiple showers were going for longer than 15 mins so a 75 that Terry recommended seems to e a good fit in my novice judgement.
The last question I have for you guys is the plumber I am working with is recommending a free air High-Efficiency 75Gal Rheem vs a Combustion air model, do you guys have a preference? The PVC for intake and Out is already set up from the current water heater.
Thanks again.
Bnick
A modulating condensing all-stainless HTP Phoenix PH100-80 (100KBTU/hr burner, 80 gallons) can sustain a continuous 24/7 full-flow shower with margin, and will outlast any glass-lined 75 gallon water heater by at least 2x in a residential application.
If the 50 gallon was almost cutting it and big enough to fill the tubs, the Phoenix PH100-55 (100KBTU/hr x 55 gallons) would be a better choice. It's the same burner to support but with only 55 gallons of buffering capacity. Even though it's nore than twice as expensive as a glass lined 75 gallon water heater, it's "worth it"- you'd only pay for the installation once every 25+ years instead of every decade .
The Phoenix Light Duty PH76-50 (only light duty in terms of commercial water heater burner size) has a 76K burner. The Westinghouse branded version of the 50 gallon version runs about 2 grand at Home Depot, but your plumber might be able to beat that price on the HTP labeled version buying direct from HTP (they're located in MA.) It's twice the burner output of a typical 50 gallon standalone, all stainless just like it's bigger-burner siblings. If your old water heater almost cuts it, the 76K burner can squeak out a single shower forever, but not with as much margin for other simultaneous uses as a 100K burner.
Or, you can save that money and go with a standard 50-55 gallon standalone, and apply the savings toward a drainwater heat recovery heat exchanger.
A drainwater heat exchanger takes heat out of the water flowing down the drain and puts it into the incoming water stream. That incoming water stream is feeding both the water heater AND the cold side of the shower mixer with much warmer water than what's coming in at the street, so it takes slower sip of hot water from the 120F+ tank to deliver 105F water at the shower head, and the water heater has to put less heat in to keep up. With a 4" x 48" or larger heat exchanger a standard 50 gallon tank with a standard 36-40KBTU/hr burner can support an almost continuous 2gpm shower most seasons at CT incoming water temperatures. From a showering perspective it's like doubling the size of the burner, but a burner that burns no fuel.
There is some pressure drop from the flow through the heat exchanger, and they're not all equal. For almost a decade
Renewability's Power Pipe series (available in the US, but you can also buy direct from the manufacturer), but more recently
EcoDrain's V1000 series completely at their lunch on both recovery efficiency and low pressure drop at high flow. A 4" x 48" V1000 returns 57% of the heat back to the incoming water stream at a standard 2.5 gpm flow rate (part of the Canadian standard test conditions) a bit more at lower flow, a bit less at higher flow. (The 4" x 72" returns fully 2/3 of the heat back, well worth it if it fits.) By comparison a 4" x 48" PowerPipe returns 49.8% which is still pretty good compared to the other competitors in this market. (I have about 10 years of service on a 4" x 48" PowerPipe in my house in MA and am totally satisfied with it's performance). As they grow taller the performance difference between those series becomes more pronounced.
But it'll increase the "apparent capacity" of the tank in showering mode by more than 1.5x (more than 2x with a 4" x 72" V1000), but does
nothing for tub filling capacity, since the drain isn't flowing when the tub is being filled. But if a 50 gallon tank fills your tubs, this would be a better overall investment than a bigger tank with a bigger burner.
For a 4" x 48" or 4" x 60" expect to pay about a grand for the unit. If you have room for a taller one the marginal upcharge is worth it- the tallest that fits is the "right" one. If it saves you a grand on water heater by letting you stick with a 50 gallon tank it's pretty much paying for itself up front, but in families that primarily shower it'll also pay for itself (installation included) in under a decade at CT's higher than national average retail natural gas rates.
