Energy Vanguard Blog

When I first became a HERS rater and went to the RESNET conference in 2004, I got to talk with David Lee, who was the head of the ENERGY STAR homes program at the time. Because I was puzzled by the paradox large homes with energy efficiency certifications, I asked him, How can a 15 thousand square foot house even be considered for the ENERGY STAR program? I’ve long been bothered by the focus on energy efficiency at the expense of energy conservation.

The standard answer that Mr. Lee and others have given to my question is that large homes are going to be built anyway, and allowing them to qualify for the ENERGY STAR label ends up helping them use less energy than they would otherwise. Yeah, that may be true, but it still bothered me that large homes didn’t even have to do anything extra to make up for all the extra kilowatt-hours they used just because of the extra size.

Now, in Version 3 of the ENERGY STAR new homes program, that changes. If you’ve read any of my other ENERGY STAR articles here in the blog, you may remember that large houses get penalized in the program starting with Version 2.5 (which is in effect for all houses permitted as of 1 April 2011 and finished before 1 January 2012).

The threshold for determining whether a home gets penalized or not is whether its conditioned floor area is greater than the floor area of what ENERGY STAR calls the Benchmark Home. As you can see in the table below, many new homes will be penalized. For example, any 3 bedroom home that has more than 2200 square feet of conditioned floor area has to pay the large home penalty.

The way this gets implemented is through the Size Adjustment Factor, a number less than 1 for homes larger than the Benchmark Home and equal to 1 otherwise. If a home that’s going for the ENERGY STAR label is larger than the Benchmark Home, the HERS Index target gets multiplied by the Size Adjustment Factor. The equation to calculate the Size Adjustment Factor is:

For example, a 4 bedroom that has 5000 square feet of conditioned floor area would have a Size Adjustment Factor of:

If the HERS Index of the ENERGY STAR Reference Design is, say, 70, the HERS Index target for the rated home would be 70 x 0.865 = 61. What this means is that if the rated home were 2800 square feet or less, it would need a HERS Index of 70 to qualify. Because the home is larger, however, it needs to get an Index of 61, or about 13% more efficient than the smaller home.

This is good! I like the large home penalty because now ENERGY STAR is acknowledging that not only is the kilowatt-hour per square foot energy efficiency of a house important, but so is the total number of kilowatt-hours that result from the extra square feet in large houses.

If you're a HERS rater, you can get the scoop on all the changes by taking one of our ENERGY STAR Version 3 classes. Click the button below to find out more and check our class schedule.

Photo of Gilbert Mansion by andrew_j_w from Flickr.com, used under Creative Commons license.