Need to look into heater heating area for possible home expansion

I am still a bit up in the air on my house remodeling plans. Rather I want to install a second bath to have a two bedroom two bath house, or stick with three bedrooms and one bath. I need to do a little investigating and see if the heater I have can heat two more rooms added onto this house, if so then the ideal solution for me would be to build a pair of bedrooms off the front or end of the house, with a second bathroom and then convert the current bath into a master bath with a his and her bath vanity and build the laundry room into the back of the new second bath to make room where the laundry room is now for a storage closet and walk-in pantry.