When a home is built using the house-as-a-system method, all parts of the home are built to work together. When upgrades such as installing insulation are completed on a home, this can cause changes or problems to occur within the home. Upgrades to an existing home can cause it to become more air tight, which in turn may require changes to the home's mechanical systems. Also, adding additional insulation may reduce the heat loss from the home enough to affect the size of the HVAC system.