Relationships behind the scenes.

Your house is a big system, made up of smaller systems.

Think of it like a car. If the transmission isn't working properly, your engine will not work well either. If your tires are low, you will lose fuel efficiency, and so on.

In a house, the major component parts include:

  • Building envelope (roof, walls, windows, doors and foundation)
  • Mechanical systems (heating and cooling systems, ventilation system, and exhaust fans, humidifiers and dehumidifiers etc.)
  • Occupants (number of people, their lifestyle, how the house is operated and lived in)
  • External environment (climate)

Each system can influence the performance of the whole house.


  • An airtight building envelope will affect how efficiently the furnace operates
  • By programming thermostats to control comfort, occupants can improve energy efficiency

Learn more about house-as-a-system design from the United States Department of Energy.