# Should We Change the HERS Reference Home’s Energy Code?

The HERS Index is a number that gives you a measure of how energy efficient a home is. We can debate how relevant that number is or how accurate is the energy model it’s based on, but the fact is that it’s being used. The 2015 International Energy Conservation Code (IECC) includes a compliance path based on the HERS Index, which they call the Energy Rating Index (ERI). Here in my state, Georgia Power has been educating home buyers on the HERS Index since they created their EarthCents program a couple of years ago. But the HERS Index is based on the 2006 IECC. Is that a problem?

The HERS Index is a number that gives you a measure of how energy efficient a home is. We can debate how relevant that number is or how accurate is the energy model it’s based on, but the fact is that it’s being used. The 2015 International Energy Conservation Code (IECC) includes a compliance path based on the HERS Index, which they call the Energy Rating Index (ERI). Here in my state, Georgia Power has been educating home buyers on the HERS Index since they created their EarthCents program a couple of years ago. But the HERS Index is based on the 2006 IECC. Is that a problem?

### The HERS Index calculation

A while back I wrote an article on the calculations behind the HERS Index, and I showed the equation below:

The important concept contained in that equation is the HERS reference home. What the calculation is doing is comparing the energy use of the home being rated to the energy use of the HERS reference home. The rated home has whatever insulation levels, airtightness, and other efficiency parameters the HERS rater enters (which, unfortunately, aren’t always what’s in the home). The reference home is set up to meet the energy efficiency requirements of the 2006 IECC.

The result is that if the number comes out to be exactly 100 (for a home with no onsite power production and a PEfrac of 1), that means, roughly, that it would meet the 2006 energy code.

### Shouldn’t we update the HERS Reference Home?

But wait! The energy code is updated every three years. Since 2006, we’ve had the 2009 IECC, the 2012 IECC, and now the 2015 IECC. Shouldn’t we update the reference home to use the most recent version of the energy code?

No. If we did update the reference home every time the code changed, we wouldn’t be able to compare the HERS Index of one home to that of a home using a different energy code. And the whole purpose of the HERS Index is to allow us to compare one home to another.

Let me give you an example. We measure weight with respect to the Earth’s gravitational pull, but let’s say Congress passed a bill requiring that everyone born on or after 1 January 2015 had to be weighed according to a pound based on the Moon’s gravity. And those born in 2018 or later would have weights based on the gravity of Venus. In 2021, we’d switch again to pounds based on Jupiter’s gravity.

I weigh 190 pounds. Someone born between 2015 and 2018 who weighed the same (that would be one huge baby!) would be 31.5 pounds. My weight twin born between 2018 and 2021 would weigh 172 pounds, and after 2021 they would 481 pounds.

As you can see, it would be a complete mess and no one would be able to compare weights easily because of all the different references for the pound.

### One thing does change

By keeping the reference home’s energy code set to the 2006 IECC, we can keep comparing the HERS Indices of different homes, but one thing does change: the HERS Index of a home that meets the current code.

A new home meeting the 2006 energy code would have a HERS Index of 100. That’s shown in the scale above where it marks 100 as the Index of a “Standard New Home.” A new home meeting more recent codes would be lower. In Georgia, we’re on the 2009 IECC, and a typical new home just meeting the code would have a HERS Index of about 92. The 2012 and 2015 codes bring it down into the 80s.

So there you have it. Despite the fact that energy codes have improved since 2006, we don’t want to mess with the HERS Reference Home.

Related Articles

Everything You Ever Wanted to Know about the HERS Index

Georgia Power Fills the Void Left by ENERGY STAR

The 2015 Energy Code Will Have a HERS Rating Compliance Path

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#### This Post Has 36 Comments

1. Brett Little says:

Good call!
Good call!

2. John Proctor, P.E. says:

Allison — we are with you on
Allison — we are with you on this, except the scale you see above should be altered. Move the "Standard New Home" and the bold line down to where a standard new home would actually be. Otherwise we are fooling everyone into thinking their home is great and that they don’t need to do anything about it.

3. CK says:

Totally agree with the
Totally agree with the following addition to the scales:&nbsp; <br />An indicator for &nbsp; <br />2006 Standard New Home&nbsp; <br />2009 Standard New Home*&nbsp; <br />2012 Standard New Home#&nbsp; <br />2015 Standard New Home#&nbsp; <br />* Current Legal Requirement in local government codes&nbsp; <br /># Some elements incorporated into current local government codes&nbsp; <br />&nbsp; <br />Codes vary by local government (federal, state, county, parish, etc.)&nbsp; <br />&nbsp; <br />Note: International Energy Conservation Codes are updated every three years and are recommended guidelines unless adopted, in part or whole, by local governments.&nbsp; <br />&nbsp; <br />Now, who bears the cost of creating this guide? I would think it would be a great builder marketing tool.

4. John Proctor says:

Interesting thought by CK. In
Interesting thought by CK. In order to simplify it, I would suggest that the line be where the current IECC code is. For local areas that are behind, it is OK to embarrass them a little.

5. Allison Bailes says:

<b>Brett L.</b>:
<b>Brett L.</b>: Thanks!&nbsp; <br />&nbsp; <br /><b>John P.</b>: I agree. The scale above, though, is the one that comes out of REM/Rate, the energy modeling software used by most HERS raters. It’s definitely time for it to be changed.&nbsp; <br />&nbsp; <br /><b>CK</b>: Even better, let’s just do away with the vague and misleading term, "Standard New Home." Just mark on the scale where the various code-built homes would fall, as you suggest.&nbsp; <br />&nbsp; <br />

6. Roy Crawford says:

I have a different view on
I have a different view on this topic. Why do we need to have a reference home? Why not just use the numerator? I know that people like a scale of 1 to 100, but this is a case where 100 lost its meaning, or at least its usefulness. If you are trying to compare two or more houses, will HERS tell you the relative energy consumption of those houses? Surprisingly to many, the answer is NO.

7. Allison Bailes says:

<b>Roy C.</b>:
<b>Roy C.</b>: Thanks for bringing up that issue. I think it’s a really useful discussion to have. One way to do what you’re talking about is with the Home Heating Index, which is the energy consumption divided by conditioned floor area and also divided by the heating degree days. That doesn’t account for cooling, but you could throw in the cooling degree days, too, although those don’t account for latent cooling.&nbsp; <br />&nbsp; <br />Your final point about not being able to use the HERS Index to compare the energy consumption in one house to that of another is also important. The HERS Index isn’t a miles-per-gallon label, despite some people saying it is.

8. Bao Nguyen-Clearsphere says:

I wonder why dont we make a
I wonder why dont we make a library for reference home, in case some one wanna compare their house to new IECC. that way people have option whether they want to compare their build to new IECC or old IECC

9. Dale Sherman says:

Nice article, Allison. I
Nice article, Allison. I like CK’s idea for updating the HERS Index. Put a PH index on there as well.&nbsp; <br />&nbsp; <br />Can we expect a future article to compare HES, HEY, HHI and HERS? I would think that that older homes would benefit more from using measured HHI, then be converted to HERS for comparison (or vice-versa). &nbsp; <br />Can we get to a single Home Star rating for all homes, or will home buyers, realtors, homeowners, and contractors be stuck with multiple rating systems? Yes, each rating system has its place, but it hinders the bigger picture of promoting common public knowledge of house MPG.

10. Mark Crawford says:

As A certified IECC Inspector
As A certified IECC Inspector and a Hers rater I find A real concern with say just cause a house meets a certain hers number then it meets energy code even tho it’s allowed in the 2015 IECC code. here in the Houston area their has been a on going problem with the city’s thinking. example – they will let any body home owner builder bum on the street do energy compliance form’s then the city doe’s the so called energy code inspections which from my knowledge none of the inspectors are certified. Then I get called in to do pressure testing ductblast blower door. then the city say’s I have to provide certification sticker..Which I won’t when 99% of house don’t meet code because of lighting issues and open wood fire places ext.&nbsp; <br />As was mentioned in your article the input does not always reflect reality.. so in conclusion with out proper inspections I don’t see how paper work alone with out certified inspection’s guarantee’s true compliance. Hers ratings are fine for reference and a good selling point only.

11. Brett Little says:

Good call!
Good call!

12. John Proctor, P.E. says:

Allison — we are with you on
Allison — we are with you on this, except the scale you see above should be altered. Move the “Standard New Home” and the bold line down to where a standard new home would actually be. Otherwise we are fooling everyone into thinking their home is great and that they don’t need to do anything about it.

13. CK says:

Totally agree with the
Totally agree with the following addition to the scales:
An indicator for
2006 Standard New Home
2009 Standard New Home*
2012 Standard New Home#
2015 Standard New Home#
* Current Legal Requirement in local government codes
# Some elements incorporated into current local government codes

Codes vary by local government (federal, state, county, parish, etc.)

Note: International Energy Conservation Codes are updated every three years and are recommended guidelines unless adopted, in part or whole, by local governments.

Now, who bears the cost of creating this guide? I would think it would be a great builder marketing tool.

14. John Proctor says:

Interesting thought by CK. In
Interesting thought by CK. In order to simplify it, I would suggest that the line be where the current IECC code is. For local areas that are behind, it is OK to embarrass them a little.

15. Allison Bailes says:

Brett L.:
Brett L.: Thanks!

John P.: I agree. The scale above, though, is the one that comes out of REM/Rate, the energy modeling software used by most HERS raters. It’s definitely time for it to be changed.

CK: Even better, let’s just do away with the vague and misleading term, “Standard New Home.” Just mark on the scale where the various code-built homes would fall, as you suggest.

16. Roy Crawford says:

I have a different view on
I have a different view on this topic. Why do we need to have a reference home? Why not just use the numerator? I know that people like a scale of 1 to 100, but this is a case where 100 lost its meaning, or at least its usefulness. If you are trying to compare two or more houses, will HERS tell you the relative energy consumption of those houses? Surprisingly to many, the answer is NO.

17. Allison Bailes says:

Roy C.:
Roy C.: Thanks for bringing up that issue. I think it’s a really useful discussion to have. One way to do what you’re talking about is with the Home Heating Index, which is the energy consumption divided by conditioned floor area and also divided by the heating degree days. That doesn’t account for cooling, but you could throw in the cooling degree days, too, although those don’t account for latent cooling.

Your final point about not being able to use the HERS Index to compare the energy consumption in one house to that of another is also important. The HERS Index isn’t a miles-per-gallon label, despite some people saying it is.

18. Bao Nguyen-Clearsphere says:

I wonder why dont we make a
I wonder why dont we make a library for reference home, in case some one wanna compare their house to new IECC. that way people have option whether they want to compare their build to new IECC or old IECC

19. Dale Sherman says:

Nice article, Allison. I
Nice article, Allison. I like CK’s idea for updating the HERS Index. Put a PH index on there as well.

Can we expect a future article to compare HES, HEY, HHI and HERS? I would think that that older homes would benefit more from using measured HHI, then be converted to HERS for comparison (or vice-versa).
Can we get to a single Home Star rating for all homes, or will home buyers, realtors, homeowners, and contractors be stuck with multiple rating systems? Yes, each rating system has its place, but it hinders the bigger picture of promoting common public knowledge of house MPG.

20. Mark Crawford says:

As A certified IECC Inspector
As A certified IECC Inspector and a Hers rater I find A real concern with say just cause a house meets a certain hers number then it meets energy code even tho it’s allowed in the 2015 IECC code. here in the Houston area their has been a on going problem with the city’s thinking. example – they will let any body home owner builder bum on the street do energy compliance form’s then the city doe’s the so called energy code inspections which from my knowledge none of the inspectors are certified. Then I get called in to do pressure testing ductblast blower door. then the city say’s I have to provide certification sticker..Which I won’t when 99% of house don’t meet code because of lighting issues and open wood fire places ext.
As was mentioned in your article the input does not always reflect reality.. so in conclusion with out proper inspections I don’t see how paper work alone with out certified inspection’s guarantee’s true compliance. Hers ratings are fine for reference and a good selling point only.

21. Craig McManus says:

When and where will the 2015
When and where will the 2015 iecc be adopted in AL, GA, or FL?

22. Craig McManus says:

When and where will the 2015
When and where will the 2015 iecc be adopted in AL, GA, or FL?

23. Leigha Dickens says:

Just for fun, I tried to
Just for fun, I tried to figure out what the "average" energy code in US is, and came up with something between 2006 IECC and 2009 IECC. Depending on if you’re optimistic or pessimistic about enforcement, a case could be made that 2006 IECC level efficiency still represents "average" new construction on a national level. &nbsp; <br />&nbsp; <br />To try this I took a a population-weighted average of the current residential energy code in each of the 50 state. This average is dragged down by the fact that there are still some states that have no statewide mandatory residential energy code at all. (I’m looking at you, South Dakota, North Dakota, Missouri, Mississipi, Colorado, Kansas, Wyoming, and Alaska…) If you give those states a "0" you’d get a nonsensical average energy code and that’s probably not a realistic representation of the energy efficiency of new construction in those states, so I gave them values between 1980 and 2006 just depending on very quick research and my personal experience with sending homes to those states. While it is true that some of those states without statewide codes do still have many local jurisdictions enforcing higher codes, and some states with one posted energy code also have local jurisdictions enforcing an even higher energy code, there are also many, many places where enforcement of a supposedly mandatory statewide code is just not happening, or is just not happening past the 2003/2006 levels that the inspector got used to dealing with. &nbsp; <br />&nbsp; <br />So in sum the average energy code in the US is kind of meaningless, but it was a fun diversion this snowy morning.

24. Leigha Dickens says:

Just for fun, I tried to
Just for fun, I tried to figure out what the “average” energy code in US is, and came up with something between 2006 IECC and 2009 IECC. Depending on if you’re optimistic or pessimistic about enforcement, a case could be made that 2006 IECC level efficiency still represents “average” new construction on a national level.

To try this I took a a population-weighted average of the current residential energy code in each of the 50 state. This average is dragged down by the fact that there are still some states that have no statewide mandatory residential energy code at all. (I’m looking at you, South Dakota, North Dakota, Missouri, Mississipi, Colorado, Kansas, Wyoming, and Alaska…) If you give those states a “0” you’d get a nonsensical average energy code and that’s probably not a realistic representation of the energy efficiency of new construction in those states, so I gave them values between 1980 and 2006 just depending on very quick research and my personal experience with sending homes to those states. While it is true that some of those states without statewide codes do still have many local jurisdictions enforcing higher codes, and some states with one posted energy code also have local jurisdictions enforcing an even higher energy code, there are also many, many places where enforcement of a supposedly mandatory statewide code is just not happening, or is just not happening past the 2003/2006 levels that the inspector got used to dealing with.

So in sum the average energy code in the US is kind of meaningless, but it was a fun diversion this snowy morning.

25. Kevin Dickson says:

I have been preaching for
I have been preaching for years that the only worthwhile rating system for homes is in dollars per year, exactly like the familiar EnergyGuide label for appliances. &nbsp; <br />&nbsp; <br />An accurate HERS score can be converted to \$/yr with a standard set of conditions.&nbsp; <br />&nbsp; <br />Dollars per year is independent of the size of the house.

26. Roy C says:

Kevin, I like your Energy Guide analogy. We all realize that one’s actual energy use will vary depending on occupancy habits, but at least this would give a number that makes sense and could even possibly be used by appraisers and mortgage lenders to help evaluate the total value of a home. I am also a member of the ASHRAE Std. 90.2 committee where some of us have been trying to introduce this approach, but I am afraid that we lost this battle.

27. Kevin Dickson says:

I have been preaching for
I have been preaching for years that the only worthwhile rating system for homes is in dollars per year, exactly like the familiar EnergyGuide label for appliances.

An accurate HERS score can be converted to \$/yr with a standard set of conditions.

Dollars per year is independent of the size of the house.

28. Roy C says:

Kevin, I like your Energy Guide analogy. We all realize that one’s actual energy use will vary depending on occupancy habits, but at least this would give a number that makes sense and could even possibly be used by appraisers and mortgage lenders to help evaluate the total value of a home. I am also a member of the ASHRAE Std. 90.2 committee where some of us have been trying to introduce this approach, but I am afraid that we lost this battle.

29. steve says:

As a rater in Colorado I feel
As a rater in Colorado I feel the frustration of home rule(each jurisdiction having its own code). However, I can say that the major population(65%) center along the front range is primarily on the 2009 and 2012 IECC.

30. steve says:

As a rater in Colorado I feel
As a rater in Colorado I feel the frustration of home rule(each jurisdiction having its own code). However, I can say that the major population(65%) center along the front range is primarily on the 2009 and 2012 IECC.

31. Steve K says:

Slightly off topic HERS
Slightly off topic HERS question. I recently purchased a 1981 home in south Florida and will be doing a complete renovation including new windows, roof, appliances, likely AC, etc. I&apos;ve been reading all your articles and find the topics very interesting, but a little scary as well – will my architect / engineers / contractors know any of this stuff as well as the should? Perhaps they do and all the calculations and plans are perfect, but the laborer who installs something does it half ass and his boss doesn&apos;t make it out to inspect before it&apos;s too late. Will anyone catch it or will my efficiency be wasted?

But I digress, back to the question. Is it beneficial to gets a HERS rating now before I do any work when I am already planning to make improvements that should by default increase the rating significantly? Should I get a detailed inspection and recommendations but not worry about a rating at this point? Any advice would be appreciated.

32. Steve K says:

Slightly off topic HERS
Slightly off topic HERS question. I recently purchased a 1981 home in south Florida and will be doing a complete renovation including new windows, roof, appliances, likely AC, etc. I've been reading all your articles and find the topics very interesting, but a little scary as well – will my architect / engineers / contractors know any of this stuff as well as the should? Perhaps they do and all the calculations and plans are perfect, but the laborer who installs something does it half ass and his boss doesn't make it out to inspect before it's too late. Will anyone catch it or will my efficiency be wasted?

But I digress, back to the question. Is it beneficial to gets a HERS rating now before I do any work when I am already planning to make improvements that should by default increase the rating significantly? Should I get a detailed inspection and recommendations but not worry about a rating at this point? Any advice would be appreciated.

33. John Proctor says:

Steve, I am afraid your
Steve, I am afraid your average HERS rater may not be much better than the folks you already know of. I suggest you get ahold of a building performance contractor.

34. John Proctor says:

Steve, I am afraid your
Steve, I am afraid your average HERS rater may not be much better than the folks you already know of. I suggest you get ahold of a building performance contractor.

1. Steve Kalka says:

Unfortunately when I search
Unfortunately when I search the BPI site for a qualified professional in south Florida, all I find is one guy from Truly Nolen, the pest control firm.

35. Steve Kalka says:

Unfortunately when I search
Unfortunately when I search the BPI site for a qualified professional in south Florida, all I find is one guy from Truly Nolen, the pest control firm.