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Energy Star ratings numbers?

Last Post 28 Oct 2008 10:43 AM by macomber. 3 Replies.

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Brock

Advanced Member

Posts:599

27 Oct 2008 08:51 PM
We just got our home energy star rating back (full blower door test and a bunch of other stuff). They said it was good, but I have no idea how it compares to other homes. Our "HERS" index rating number is 46 (said it had to be below 100) and our heating energy intensity is .84999999. Again they said that is good, but I don't know where that really falls. Is the .849999 number a BTU / sq ft? at some given temp? I saw our heat calcs, but I either didn't get a copy or lost them. I thought I remember a number around 1.5, but I could be way off.

Green Bay, WI. - 4 ton horizontal goethermal, 16k gallon indoor pool, 3kw solar PV setup, 2 ton air to air HP, 3400 sq ft

macomber

New Member

Posts:3

27 Oct 2008 11:21 PM
If one knows the rate of consumption of a furnace or boiler (Btu/hr), then by measuring the time it is operated over a given period in which outside temperature is tracked, it is possible to produce a simple but useful weather-adjusted index of consumption, Btu per heating degree-day (Btu/HDD). This is calculated by the elapsed time multiplied by the firing rate of the furnace (or boiler), all divided by the heating degree-days for the appropriate reference temperature over the same period. Dividing by the heated area gives the heating energy intensity (Btu/ft²-HDD). A HERS index is used to compare a "code" home to your home. A rating of 100 means your home used energy on par with an identical house that was built just to code. Your home uses 46% of the energy it would have used if it had been built to code. FYI, an Energy Star rating requires a HERS index of 80-85...way to go!