The EnerGuide Rating System changed from a 0-100 scale to Gigajoules per year back in 2016. There are a lot of houses out there with these ratings labels on them, and a lot of industry people still refer to the zero to one hundred scale in conversation, because it was an easy shorthand for us.
Under the old system a rating of 100 represents a house that is airtight, well insulated, sufficiently ventilated and requires no purchased energy, while an old leaky house with no insulation would come in somewhere under 50.
Why did it change? A few reasons.
First, as we’ve all been brought up through schools that graded us on a percentage basis, we’re conditioned to think that 75 percent is a decent grade, and therefore, we don’t really need to work harder to get to an 80, which was the equivalent of an R2000 house under the old system.
Hard to Scale Up
Second, moving past 80 was really, really hard, as each point was worth something along the lines of thirty-five hundred to five thousand gigajoules of energy used over the course of a year. The higher up the scale, the tougher it got to level up.
It was easy to get a house from say 65 to 75 with relatively inexpensive measures like air sealing, insulation blown into empty walls, boosting attic insulation, swapping out old heating equipment for higher efficiency new units. But then, that pesky building science and unintended consequences kick in when the house gets tighter and better insulated and then you need to add more complex and expensive measures like controlled mechanical ventilation and make up air for combustion appliances and, and...
We’re talking mainly about retrofits, but new construction was not much different in terms of the measures required to move up the scale. Getting to 100 was nearly impossible, and very, very expensive.
Third, what does it mean to improve from a 65 to a 75 under this point system? It’s not as simple as oh, that’s a 10 percent reduction in energy use! A one-point improvement on the old rating scale could represent a 3 to a 5 percent reduction in energy consumption.
Fourth, once we got on the path to Net Zero Energy in housing, it was confusing to have a rating of 100 for a house that essentially had zero energy costs.
More Gigajoules, More Energy Use
Now, it’s much more user friendly: the higher the gigajoule per year number, the less efficient the home is. The closer to zero the gigajoule per year measurement is, the more efficient the house is. Homes that produce more energy than they use have a rating of zero.
Why gigajoules? A gigajoule is a unit of measurement for energy that doesn’t care about the fuel source – electricity, natural gas, oil, propane or wood. BTUs, kilowatt hours and other measurements are converted, and now we’re comparing apples to apples, because the energy use rating is fuel neutral.
The gigajoule per year system also gives a better understanding of the impact of energy conservation measures. If your EnerGuide rating goes down from 100 GJ/year to 90 GJ/year – that’s a 10% improvement.
What didn’t change is the fact that EnerGuide ratings don’t reflect your actual energy use, because of occupant behaviour. The rating is based on standardized usage regimes for thermostats, hot water usage, and lighting/appliance loads under standardized occupancy. This means the rating reflects how much energy is required to heat and cool the house under standard conditions, as opposed to how an individual household might use energy. There’s also an Energy Intensity Unit that is also on the label, showing gigajoules per meter squared. This allows homebuyers to compare the relative energy costs of different houses they are considering.
So gigajoules per year it is.