Reading an EnerGuide label for a home

What is an EnerGuide rating?

The rating comes from a standard model that a licensed energy advisor runs after inspecting and testing the house. It estimates how much energy the building would use under standard operating conditions: a fixed temperature setpoint, standard hot water use and standard occupancy. Your own bills will differ because your habits are not standard.

That separation is a feature. It rates the house, not the occupants, so two different families in identical houses get the same number.

How do you read gigajoules per year?

A gigajoule (GJ) is a unit of energy. Convert it with this relationship: 1 GJ is roughly 278 kWh. A house rated at 100 GJ a year is modelled to use roughly 27,800 kWh of energy for heating, cooling, ventilation and hot water, counting all fuels together. Lower is better.

Older labels and some reports also show a 0 to 100 score where higher is better. Check which scale the document uses before comparing two homes, because the direction is opposite.

What does the rating include?

• Space heating and cooling, including the efficiency of the equipment.
• Water heating.
• Ventilation, including any heat recovery ventilator.
• Often a base allowance for lights and appliances, depending on the version of the scheme.

Fuel type is part of the picture. Heat from a heat pump counts as electricity used, and gas heating counts as gas used, all converted to the same unit. A house can therefore improve its number by switching equipment, even without touching the walls.

A worked comparison of two houses

Take two houses of the same size. House A is rated at 130 GJ a year and House B at 90 GJ. The gap of 40 GJ is roughly 11,100 kWh of modelled energy each year. If a unit of energy costs a given amount in your region, multiply that gap by the local price to see the yearly difference, using current rates from your own bills. Because the model assumes standard use, the real gap for a particular family could be smaller or larger.

The comparison is sound only if both ratings come from the same version of the scheme and cover the same fuels, which is worth asking about.

A final caution: a rating belongs to the house as it stood on the evaluation day. After a renovation, a new furnace or a new addition, the old number no longer applies, and a fresh evaluation is the only way to update it.

How is it used to compare homes and plan upgrades?

Buyers use a rating to compare two listings of the same size. Owners use a before and after pair to see what a retrofit achieved. The home energy audit is how you get the first number, and the report lists the upgrade steps and their modelled effect.

Size matters. A large house can show a higher total even if it is well built, so some reports also give a figure per square metre. When comparing homes of different sizes, look for that normalised value or ask the advisor to explain it.

The label can also be a stepping stone for certification, such as R-2000 or ENERGY STAR new homes, which use their own technical requirements and verification.

Limits of the rating

The number is a model. It does not track weather, lifestyle, extra freezers, a hot tub or a home office. It also does not reflect solar generation in the way a utility bill would, so a house with panels needs careful reading of how the report treats them. At Drake Landing, the question was answered by measurement rather than a model: the performance results page lists the monitored solar fraction, which reached 100 percent in the 2015-16 heating season for the 52 homes.

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