Originally posted by @Alex P.:
You need to have your electrician do a load demand calculation on the apartments to see if your service is adequate. No one on here is going to be able to give you accurate information without a lot more info. It's not as simple as just adding up appliances.
It actually is as simple as adding up built-in/permanent appliances (nameplate KW) and just knowing the sq footage of the apartments. It's the optional demand load calculation method (2014 NEC).
How many KW is the the baseboard heaters?
Assuming 600 sq ft apartments:
Lighting 1,800
Small Appliance 3,000
Refrigerator 1,400
Microwave 1,400
Stove 12,000
Heat 5,000 (assumed)
(A/C not calculated since smaller than heat)
(Assuming no disposals, exhaust fans, or other built in appliances.)
Total: 24,600 x 16 = 393,600
Your demand factor would be 39% for 16 apartments.
393,600 x .39 = 153,504
153,504/ (assumed single phase 3 wire 240v service)= 639.6 amps not including your building meter. Note if you have 3 phase service this number will be lower.
You can calculate the buildings meter separately. Demand factor will differ.
This also assumes only one service run per apartment.
Just because you are upgrading the main panel from 60 to 100 amps does not mean you will be using more power.