My house is poorly insulated but retains much more heat. Its not uncommon to be 30 or more degrees warmer inside than out without any other heat sourses .The main reason is a south facing enclosed solar porch that generates a tremendous amount of heat. Its easily controlled with a whole house fan if it gets too hot but i like to save it for overnight when the sunporch stops generating heat. ANy avarage house will be 10 or more degrees warmer than outside temps due to Body heat and appliances like your refrigerator and dryer if its vented internally and cookin stove.