I currently have an older 125amp QO square D panel with 16 total spaces. I'm trying to update some of the electrical in my house and have some overloaded circuits that I'm now separating and dedicating certain appliances. I don't have a lot of space in my current panel to re-feed some circuits or expand. Few things to note: My calculated total load for my home is approximately 63 amps (Assuming I calculated that properly). I have roughly 1600 SQ ft and all gas appliances. Vast majority of said appliances are less than 10 years old and of higher efficiency. I did base my calculations using the nameplate value on all my main appliances.
I want to add AC this coming spring/summer. Otherwise I don't plan on adding more to the home pending I win the debate to not get a hot tub.
Tandem breakers are not much of an option since it's difficult to find them in the older QO style. Home Depot has them but with a "hook" for the point of attachment and that is not compatible. Furthermore, updating some things to code for GFCI or AFCI requires those to be breakers and not outlets since they would be inaccessible.
Ideally, I would prefer to upgrade the main service panel for one with a main disconnect and significantly more spaces at the very least and running a sub panel to my attached garage for convenience. Upgrading the panel with everything going on right now doesn't seem ideal plus wrestling whether or not to just do a service upgrade at that point and have peace of mind that I will have more than enough room for expansion if needed.
With all that being said. Can I place a 125amp sub panel with my existing 125amp main service panel? Feels weird that the sub panel would be the same amperge rating and having more spaces. Otherwise, I'm wondering if I can use a 125amp rated panel with 100amp breaker and #3 Cu wire to get the more circuit spaces. Also, would anyone recommend if I should place the AC circuit on the main or sub panel?
Looking forward to any advice. Sorry to be long wimded.
***Note: sub panel would be on the same wall as the main panel and very close to one another. The additon of AC would be on the exterior of that same wall right by the service entrance.