Dear sir; I am replacing my 1956 heater that is still functional and adding air to the house, being told by a/c heating people I need a sub panel. Have had electricians come out telling me I have 100amp panel and one guys says the main shut to shut off whole panel maybe in attic or in a wall covered up? They say it has a split panel with a 50amp that shuts half off which covers pretty much of all in the house. The circuit breakers are bulldog push matic type and there are several empty places in the panel. If you would like pictures I can send. If I counted right there are 19 breakers. From top to bottom ii position #1 & 2 are 4(1ea) 20amp Had P2020 on side. #3 & 4 50amp (1ea) cat#31150 on side. #5&6,#7&8 (1ea) 30amp cat#31230, #9&10 (1ea) 50amp cat same as other, #11 (1ea) 15amp cat # 3115,#12 (1ea)20amp cat#31120,#13(1ea)20amp, #14 (1ea)15amp,#15&16 (1ea)20amp,#17(1ea) 20amp, #18 (1ea) 15amp, #19 (1ea)15amp #20 Blank. If you assist me I would appreciate it.

What is the question you have?

What does this mean?

one guys says the main shut to shut off whole panel maybe in attic or in a wall covered up?

I highly suggest the panel be changed out, considering the age of the entire service, everything needs to be changed.

A load study needs to be done to size the size, a 100 amp may be enough, or a 200 amp may be needed.

You have a "split panel", top and bottom 50 amp CB should shut off each half.

Pictures are always welcome.

You should SERIOUSLY consider upgrading your 100 amp service to a 200 amp. Not knowing what your loads are but guessing by the size of the breakers that your panel may be taxed already. Adding air conditioning may be enough to overload the panel. Have a qualified electrician do a load calculation for you. I'd be surprised if what you have is adequate. What devices are on the 50 and 30 amp breakers?

Missouri, keep in mind, two of the 50 amp breakers are the Mains.