New BA3 Water Heater

The current water heater is 12 gallons, 120V, 1500W element. The space is narrow: 20" with a 15" opening. The closet is about 35" deep and we could go 8' tall if we reconfigure the shelf. There is 240V power on the exterior wall, so it shouldn't be too hard to bring it inside. The current Whirlpool water heater has no TPM--we probably want to route a PVC pipe outside.

Conventional

Casey found AO Smith ENT-40 40-gal 4500W. It is ~$360, 18" diameter and 60.25" high (Tall).

Tankless

If we have 240V, we can consider tankless. We have a 50A circuit breaker, so we're limited to 12kW. The First Hour rating of the conventional 40-gal unit is 53 gallons.

The EEMax HomeAdvantage II might serve our needs. It only draws 33A, meaning 8kW. EEMax has models that require multiple circuits, up to 36kW. It seems more like a point-of-use heater, though, so that you get instant hot water at a sink.

I don't think we can combine a conventional and a point-of-use tankless on the same circuit.

I think we gave up tankless because it needs major amounts of electricity.

On average, an 8.2-minute shower uses 2.1 gallons per minute. (Source: https://www.home-water-works.org/indoor-use/showers).

Gas

Another option to consider is that we can run natural gas from the basement over to the bathroom. We certainly have the gas capacity. That definitely requires a licensed plumber and a building permit, but then we would have more options, such as this Rinnai Gas Tankless Water Heater. We could install it outside, so the gas line wouldn't have to enter the house, and we would have only plumbing inside the closet. We might want to replace the shower stall with a larger one (although drain position would have to stay the same).