Within the past few years I had our older breaker panel, 1971, and sub-panel, 1981 (that was installed when pool was built, by previous owners, but other things coming off it too) replaced with a much larger panel. Utility company also up-sized our transformer, for free

. Out here each house has its own transformer before entering the house. Anyway the electrician, my favorite, informed me that the old sub-panel addition was way out of code.
So make sure it is "to code".
"Favorite" electrician informed me that city would replace transformer for free especially since the old one was sized for 1971. We have a lot of transformers "blow" out here with trees and extreme winds and occasional high up tree fires. Used to be when we lost electric out this way, at least once a month but usually more often, it could take elec. co. up to 24 hours to find and fix it. Since they've built some multi-million $$ homes out here (our three houses, around a common area, at end of dead end road, surrounded by protected parks and habitats is the "ghetto" area out here :lol: ) they've totally replaced all old service coming from sub-station, so it's only out every few months, usually blinks a few times during storms, and when it goes out they can get it fixed in a few hours, usually.
BTW.... I mainly had the new panel installed when we replaced a large tank water heater with two 220v, on-demand heaters installed in parallel. They each surge to 13 kw when they first come on and caused many things to dim when they came on. (We don't have gas or sewer out here.) And, yes, we did have to run much heavier wiring, in individual rigid conduits, to each heater, but luckily around ceiling of garage so virtually unnoticeable. The standard wiring for a 220v tank water heater is smaller than required for the 220v on-demand heaters. And, no, I wouldn't recommend large, electric on-demand
whole-house heaters, as they weren't able to keep an even temperature supply to bathrooms on second level. Gas is a different story though; they work great. Electric worked great for downstairs bathroom, though, and only need one. Other one, now services courtyard/greenhouse and for washing dogs outside. Kitchen and laundry are on separate heater.
Interestingly enough, I'm going to have to add a new sub-panel soon, for more feed to our living area. It's going to have to run from panel around 1 1/2 sides of house through even more rigid conduit. Running that stuff, and attaching to brick wall, is pretty costly if you have an electrician do it.
BTW... we can't run wiring inside our house in virtually all the downstairs (the upgraded and additional communication lines to our living area and office also had to be run outside) nor underground much, so plan ahead :!: :!:
AND PLAN FOR MUCH MORE THAN YOU CAN EVER IMAGINE NEEDING.