For an interior room to be considered as living space, there must be some form of “Permanent Heat”. The heating source must be capable of maintaining 68 degrees F at 3 feet above the floor and 2 feet from the walls. As we sleep on beds, that is how the 3 foot above the floor rule was figured out. 2 feet from exterior walls is because all winter snows can make the windows cold as ice. And this rule currently does not apply to Hawaii. And portable heaters are not allowed as a permanent heat source. IRC 303.9