Comments on: ENERGY STAR Homes Version 3 – Lowering the HERS Index

By: David Butler

David Butler — Wed, 24 Nov 2010 21:32:11 +0000

Lee, AFAIK, volume has no
Lee, AFAIK, volume has no impact on the HERS score with current version and I haven't seen anything indicating that's going to change.

Oh, there is one thing. If you enter infiltration in terms of ACH (bad idea in any case), the program will use the volume you enter to convert to CFM. If the house is tight, even that won't affect the index unless you've select a mechanical ventilation system.

By: Lee Thompson

Lee Thompson — Wed, 24 Nov 2010 20:48:27 +0000

Does the volume enclosed by
Does the volume enclosed by the attic come into these calculations? I have been looking around at homes in the Midland, TX area and most of the older homes have low-peaked roofs, and most of the newer homes have high-peaked roofs. Are there building-science-related pros and cons for attic volume, or is that merely a matter of aesthetics?

By: Allison Bailes

Allison Bailes — Wed, 24 Nov 2010 02:01:49 +0000

David, that 35% must be based
David, that 35% must be based on the ENERGY STAR team's initial look at the impact of the new requirements on energy efficiency. It's averaged over all climate zones, I'm sure, and that may represent the difference between the their 35% and my 27%. Although my sample size is fairly low, the 99% confidence level would be 73±3, not big enough to include their 35%.

ES V3 is actually tied to both the 2009 IECC and the 2006 (or 2004) IECC. The former is referenced in the new guidelines as being the minimum that homes must reach in each area. The latter comes in with the HERS Index, which is based on the HERS Reference Home as defined in the 2006 HERS Standards. The Reference Home is based on the 2004/2006 IECC.

I've posted my article in a few places on LinkedIn and Home Energy Pros with the hope of getting input from people in other climate zones.

By: David Butler

David Butler — Wed, 24 Nov 2010 01:12:54 +0000

Allison, the following is
Allison, the following is from the ES 2011 FAQ dated April 2009.

"The proposed performance path provides the opportunity to more accurately associate the ENERGY STAR 2011 threshold with homes... that are roughly equivalent to homes 35 percent more efficient than the 2006 IECC."

Does this mean ES v3 is pegged to the 2006 IECC? And what about the 35% number? This appears inconsistent with the index targets (pre-SAF) you came up with.