Abstract
The existing calculation method for heat gains and building energy balance, which has been approved in Latvian legislation, uses approximately 70 equations and formulas to calculate heat gains. By carrying out a study on apartment building heat gains it was concluded that these heat gains for different types of buildings are located in relatively narrow range. This means that it is possible to simplify heat gain calculation method while making buildings energy balance. By using standard ISO 13790:2008 a simplified calculation method which describes heat gains in typical apartment buildings in Latvia was developed. This calculation method consists of one equation.