1050sqft house is currently running on 100 amp service with all electric: furnace, water heater, stove, etc. going to convert attached garage into master bed/bath plus additional room. Garage is 12x24. Do I need to have converted to 200 or will 100 be plenty for that size of house?

What electrical devices will you be planning for the addition? Heating? Hot water? How will you heat the bathroom. Code today is a minimum 100 amps and in looking at total electric loads you have you may be stretching if you add more circuitry.

What electrical devices will you be planning for the addition? Heating? Hot water? How will you heat the bathroom. Code today is a minimum 100 amps and in looking at total electric loads you have you may be stretching if you add more circuitry.

Will branch off CA/Furnace to heat additional rooms. The house also has a well so the pump is ran off service. So there will be the CA/Furnace, water heater, softner, well pump, stove, washer, dryer, and the normal outlets and lighting.

Personally I would upgrade. You will be increasing the square footage by 35% .Just with that alone at 3 watts per sq. ft equals 40 amps for general circuitry, not counting kitchen, heater, well, stove etc. I will have to assume this is an older house. Do you know what the utility supply is? Capable of 200 AMPS or will they need to run a new service?

Personally I would upgrade. You will be increasing the square footage by 35% .Just with that alone at 3 watts per sq. ft equals 40 amps for general circuitry, not counting kitchen, heater, well, stove etc. I will have to assume this is an older house. Do you know what the utility supply is? Capable of 200 AMPS or will they need to run a new service?

Built in 1952, don't know what supply is yet. Just a house I'm looking to purchase and wanting to figure out necessary updates for addition.

Yea, I guessed older. Does it have 2 or 3 prong wiring? I would bid low enough to cover the cost of upgrade-varies but figure $4000 +/-.