Generally, an average-sized home of this size will require approximately 100-120 BTUs per square foot in order to achieve comfortable temperatures throughout all its rooms. There are various factors which can influence the necessary boiler size, such as whether or not your home has thick insulation and if additional appliances (such as a hot tub) require heating as well. To determine the exact BTU boiler needed for a 2000 sq ft house, it is best to consult an experienced HVAC professional. They can evaluate your specific needs and make sure your family will receive adequate heat in an efficient manner.