How many spare breaker slots do you have. If you have 2 you can install a 2 pole 30 amp breaker and run #10/3 cable for the WH. If you have the spare slots don't concern yourself with a load calculation. Your panel is designed to hold as many breakers that it will accept.
If you do not have any spare breakers you can use tandem breakers to free up some space. You must be sure your panel will accept tandems and how many! 100 amp services are not always to small. In fact it may be just right for your house.
If you do not have any spare breakers you can use tandem breakers to free up some space. You must be sure your panel will accept tandems and how many! 100 amp services are not always to small. In fact it may be just right for your house.
