Circuit breaker panel capacity

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Here is a general question, I am planning a project and will eventually get all proper permits but I want some advice to determine if this step is necessary

I am planning to install a steam room in a new bathroom and it requires a

35A, 220V dedicated breaker. My house has a 100A service panel with one 50A to the range, one 35A to the drier and about a dozen 20A wall plug circuits.

The question is: Is it likly that I will need to simultaniously upgrade the service panel to 150A when adding this circuit? What is the rule about the maximum capacity of a service panel?

I know it depends on where I live (CA) etc. I am just looking for direction before I go in for permits and get rejected for omitting something important.

[Travis Jordan]

The service load needs to be calculated per NEC 220-31. Add up the numbers and see what you get.

220-31. Optional Calculation for Additional Loads in Existing Dwelling Unit

For an existing dwelling unit presently being served by an existing

120/240-volt or 208Y/120-

volt, 3-wire service, it shall be permissible to compute load calculations as follows:

Load (kVa) Percent of Load

First 8 kVA of load at 100

Remainder of load at 40

Load calculations shall include lighting at 3 volt-amperes/ft2 (0.093 m2); 1500 volt-amperes for

each 2-wire, small-appliance branch circuit and each laundry branch circuit as specified in

Section 220-16; range or wall-mounted oven and counter-mounted cooking unit; and other

appliances that are permanently connected or fastened in place, at nameplate rating.

If air-conditioning equipment or electric space-heating equipment is to be installed, the following

formula shall be applied to determine if the existing service is of sufficient size.

Air-conditioning equipment* 100%

Central electric space heating* 100%

Less than four separately controlled space-heating units* 100%

First 8 kVA of all other loads 100%

Remainder of all other loads 40%

*Use larger connected load of air conditioning and space heating, but not both.

Other loads shall include the following:

1. 1500 volt-amperes for each 20-ampere appliance circuit

1. Lighting and portable appliances at 3 volt-amperes/ft2 (0.093 m2)

2. Household range or wall-mounted oven and counter-mounted cooking unit

1. All other appliances fastened in place, including four or more separately controlled spaceheating

units, at nameplate rating