House As a System

What is the House as a System concept?

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.

Where do I start to reduce drafts and improve my home?

The first step to reducing drafts is to identify the air leakage areas throughout your home. Although you might feel drafts and see air leakage areas around windows and doors on the main floor, in most homes, the most significant air leaks are often found in the attic/top floor and basement/lowest floor and are often hidden. This is due to the stack effect: In a heated home, less dense warm air rises and expands, creating a higher-pressure area near the top of the house. As cold air pushes into the lower portions of your home it forces the lighter, warm air up and out through leaks at the top.

In general, the priorities for air sealing are:

  1. Large holes regardless of location (plumbing or electrical penetrations, ductwork through unconditioned spaces, large gaps under doors, masonry chimney chaseways)
  2. Smaller holes on top floor ceiling/attic (pot lights, ceiling penetrations around fixtures, attic hatch, attic knee walls, service shafts, etc.)
  3. Smaller holes on the bottom floor (hose bib penetrations, cracks on exterior and foundation walls, basement doors, electrical boxes, gas lines or oil fill pipes that go through exterior walls, etc)
  4. Smaller holes on main floors (windows, doors, top and bottom of baseboards, fireplace dampers, electrical outlets, switches)

For a more in depth air sealing analysis of your home, you can have an EnerGuide Home Evaluation performed on your home to find any obvious or hidden drafts that need sealing. A program-qualified energy advisor will come to your home, perform a blower door fan test/depressurization test and look for air leaks. The advisor will also use the data from the depressurization test and calculate the air leakage rate for your home. The Renovation Upgrade Report provided by the energy advisor will include a prioritized list of draftproofing measures for your home.

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

What are the priority areas for insulation?

Insulation works like a giant sleeping bag. It wraps the house in a layer of material that slows the rate at which heat is lost to the outdoors.

  • The priorities for adding insulation to your home will depend on the pre-existing insulation levels in your home.
  • If there are areas of your home that are not insulated (for example your main floor or basement walls) this would generally be the priority place to start.
  • There may also be under-insulated areas in your home which would benefit from adding insulation. See How do I know if I have enough insulation in my attic.

For more information on priority areas to insulate in your home, visit BC Hydro, have an EnerGuide Home Evaluation with a Program Qualified Energy Advisor or speak with a professional insulation contractor. Check the Better Business Bureau for reputable contractors in your area. See our Hiring a Contractor FAQ section for more information.

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

How do I know if my heating and/or cooling system is properly sized for my home?

To ensure optimal energy performance and comfort for your home, it’s important to install appropriately sized equipment that will heat and/or cool your home sufficiently. Keep in mind that newly retrofitted homes may have smaller heating and cooling needs than they did prior to upgrades and renovations, particularly if you are making changes to your building envelope such as draftproofing and upgrading insulation.

If you are in the market for a new heating system be sure to ask your heating system contractor to explain how the system they are selling is appropriately sized for your home.

Here are some signs to indicate that your heating and/or cooling system may not properly sized for your home:

  • Interior Temperatures Not Maintained: If you find that some spaces in your home are not comfortably heated or cooled, your existing system might be too small to support your home’s heating or cooling demands. If you find that comfortable temperatures are difficult to maintain, you should also check your home’s air ducting or hydronic piping system to ensure that that the distribution system is balanced and that your ducts or pipes are insulated, sealed and properly connected.
  • Heating or Cooling System Short Cycles: If your heating or cooling system turns on and off frequently, it may be too large for your home. Although some people may think that bigger is better, an oversized heating or cooling system will be less energy efficient and may reduce the overall comfort of your home. The frequent on/off short cycles can also put more stress on the system’s components and shorten its lifespan.

For more information, visit the Canada Mortgage and Housing Corporation.

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

Why is it important to select the right windows for my home?

When selecting windows for your home, it is important to consider how different glazing options will affect both the energy performance and thermal comfort of your home. A window’s ability to block or admit incoming solar energy is measured by its solar heat gain coefficient (SHGC). Solar gain from windows can be to the benefit or detriment of a home’s comfort depending on factors such as climate, window orientation, and the amount of window shade/ cover. In colder climates, high solar gain can be beneficial and reduce the heating load for your home, whereas in a warm climate, high solar gain can cause overheating.

Overheating caused by solar gain from windows can lead to decreased comfort and increased energy demand on your cooling systems. To avoid this problem, windows facing south, west and east, susceptible to high solar heat gain may benefit from low-SHGC windows. Windows facing north that receive minimal sun exposure, or other windows that experience significant shade/cover, may benefit from high-SHGC windows.

Talk to your window installer to help choose the best windows for the comfort of your home.

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