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.

AutoTracer wrote:
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.

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

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

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

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

units, at nameplate rating