Replacing a heater downtown is usually constrained by where the old one is and how you get the new one there.
Access first, model second
Attic installations reached by pull-down stairs, closets sized for a narrower tank, and staircases that will not take a full-size unit. Sometimes the honest answer is a different form factor rather than a like-for-like swap. That is a site visit question, not a phone quote.
Tankless suits the peninsula
Soft water means less scaling risk than the outer suburbs, and the space saving genuinely matters in a house with no spare square footage. Provided the gas supply and venting can be brought up to the load, tankless is often the better answer downtown — which is not what we would say in Summerville.
Bring the installation up to code
Expansion tank, correct pan and drain routing, proper venting, and seismic-free but secure mounting. Older downtown installs frequently lack the pan and drain, which is the single most consequential omission in an attic.
Permits
Replacement is permitted work. Unpermitted installations regularly surface during a peninsula property sale and hold up closing.