Although separate from each other – your insulation, heating and cooling system, windows, doors, ventilation, and exterior walls, foundation and siding make your house operate as a multi-component system, where all the components are interactive. Because your house operates as a multi-component system – sometimes energy retrofits to one component of your home can affect other components of your home in unintended ways.

Before starting to improve the efficiency of your home with one retrofit, it is a good idea to get advice to ensure that your investment in home energy improvements meets your expectations and that you will not be causing new issues while resolving old ones.  Planning your retrofits within a house-as-a-system approach will also allow you to create a long-term home energy improvement plan and will provide guidance on the recommended order in which to complete energy retrofits.

House-As-A-System Cause and Effect Example

Reducing air leakage by completing air sealing or installing new windows provides more comfort to the occupants and protects the envelope from moisture damage. However, reducing air leakage also increases humidity levels inside the house since less water vapour can escape through your old windows or cracks that have been sealed. This humidity can cause condensation on windows, resulting in the potential for mould growth and damage from accumulating moisture. To reduce humidity levels, moisture and condensation a home may now need more and better mechanical ventilation. The lesson here is that a change to one component of the house can have an immediate effect on another component. Many small changes over time can also affect the balance of the system.

House-As-A-System Considerations with Common Upgrades

Windows & Doors

Well-constructed and installed high efficiency windows can provide year-round savings and comfort by reducing heat loss reflecting heat back to its source. This keeps your home cooler in the summer and warmer in the winter, while also eliminating drafts through window openings.

  • House-As-A-System Considerations:
    • Reducing air leakage through new windows may require the installation of additional, or better ventilation to manage humidity and moisture within the home.
    • Installing new windows in an under-insulated home may not significantly reduce energy bills or improve home comfort.
    • For more information, check out our Windows and Doors FAQs

Heating & Air Conditioning

A well installed high efficiency heating and cooling system can reduce dollars spent on utility bills, shrink your environmental footprint, keep fresh clean air circulating through your home while maintaining an even, comfortable temperature.

  • House-As-A-System Considerations:
    • Installing a high efficiency heating and cooling system in your home before addressing air leakage issues or upgrading your insulation may result in the installation of an oversized heating system that does not provide the energy savings or comfort you would expect from your investment in a new system.
    • For more information, check out our Heating and Cooling Systems FAQs and Water Heating Systems FAQs


Well-installed insulation keeps the heat in your home, can reduce air leakage and drafts, stops your heating or cooling system from working overtime and can provide year round comfort with less costly energy bills.

  • House-As-A-System Considerations:
    • Like other energy efficiency products, insulation needs to be correctly installed to function effectively.
    • Before insulating, air sealing may need to be completed on penetrations into walls and attics to prevent moisture from damaging new insulation.
    • If pre-existing attic insulation that is being topped up is wet, mouldy or contains vermiculite it needs to be removed before new insulation can be added.
    • If you discover rats or mice (rodents) in your insulation, it is important to eliminate the problem before adding more insulation
    • For more information, check out our Insulation FAQs

Mechanical Ventilation

Well installed and properly sized high efficiency ventilation systems provide good air circulation and controlled humidity levels. This results in a more comfortable, cleaner, and fresher home.

  • House-As-A-System Considerations
    • An air tight home with insufficient ventilation may have issues with indoor air quality, high levels of humidity, and insufficient air circulation for a healthy home.
    • A home with too much ventilation may be uncomfortable and be costly to keep warm in the winter.
    • For more information, check out our Draftproofing FAQs and Ventilation FAQs

Did you see a building science or energy efficiency term you did not understand? Check out our glossary.