Is anyone aware of HERS tracking 5 years or more after new construction?  I am looking for a study that may provide how valid the HERS rating might be 5 years or more after new construction.  Comparing the original HERS Rating to one later assuming no changes have been made to the house would provide credibility of the Index after new construction.  A representative of Fannie Mae questioned using the HERS Index after new construction.  It is hard to believe this type of tracking is not being done somewhere to give answers to the secondary market and public.

If changes to the structure are made or maintenance is not as envisioned, it would explain a difference. Any information you may have would be helpful.  Including the HERS Rating in the MLS and other databases going further presents this question that begs for an answer.

Tags: Energy, HERS, Index, MLS, Rating

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I am a HERS Rater/QAD, and am unaware of any HERS index tracking studies.  The reason is probably that the HERS Index is designed as a means to compare one house's potential energy performance relative to other houses, not to track the energy use of one house over time.

Much like a car that is rated at 25 MPG, a house with a 75 HERS Index will pretty much ALWAYS be a house with a 75 HERS Index.  It gives you an energy efficiency metric for the house that can be used for comparison.  The more appropriate and accessible tracking metric over time for your purposes might be the monthly utility bills.

The disclaimer "Your Actual Mileage May Vary" also applies to this analogy!  Just as two different drivers may get different actual MPG in the same car based on their driving habits, a homeowner that keeps their thermostat at 57 degrees in the summer and 80 degrees in the winter is going to have a vastly different experience with the energy usage of the same home as someone who keeps the temps at 68 in the winter and 78 in the summer!

Another reason for the lack of studies is that a HERS rating on a new home is not likely to change dramatically, if at all, in 5 years time.  There may be a variance in air infiltration and/or duct leakage testing due to aging of seals, weather differences between test days (wind, etc.) or "settling", but the rated features of a home are most likely going to remain in place, long-term.  Barring a dramatic change in testing results, the impact to the Index is not going to be significant.

A typical room addition, properly built to current code standards, is also not likely to alter the rating significantly either.  Obviously, adding 2000 SF to a 1500 SF house, or adding a 2nd story is another matter.  However, I wouldn't expect such a large scale project to occur to a 5 year-old house.

There is one entry in HERS that can factor any maintenance issues with mechanical systems, but it does little to impact the overall rating score.

The biggest part of any HERS score variance would most likely come from the software input choices of the individual performing the rating, if they are different people.  Properly trained raters looking at the same house could still vary in their ratings by +/- 10%.  Believe it or not, this is usually a far greater potential variable than the the index change from adding a few inches of insulation, or new windows.  A proper study as you are suggesting would need to use the EXACT same rater to come back on a day with the same daily weather conditions.

These are my personal opinions formed from field observations over the years.  Hope this helps!  Please let me know if you have any questions.

Craig Senglin

Energy IQ


I totally understand what you are saying about the HERS Index.  I am familiar with how it is tested and the basis for testing.  The question that recently arose involves the secondary mortgage market - how long is that HERS Index reliable for an appraiser to rely on?  Without some factual data -studies tracking houses, it will be next impossible to convince them that the HERS Index is good for any comparison of sales other than new construction.

You might call RESNET, as they would probably have a definitive answer, but to my knowledge, once a home is rated, the rating should remain fairly static throughout the life of the house (provided no significant improvements are made).

Since the appraisal and home inspection world is centered on establishing "as-is" condition, and they have little understanding of energy performance, getting an appraiser to understand and buy-in would, as you say, be a chore.  Probably easier just to have a new HERS rating performed.

Ratings and software combine to make estimates

True analysis comes from Consumption: Utility data, past bills, etc

Occupant behavior can skew the results 50% or more

Structural modifications can induce further changes

I've done one year studies here in New England with homes I have weatherized.  Results varied depending upon parameters.

I found 20-40% savings were the norm, based on my data collection

I'm 5 years out, now.  If I get some time I'll try and reSample

Hi Sandra,

I think the realistic approach has to be the score "when manufactured" or "when upgraded".  Essentially the value of a HERS rating or any other improvements decline with time.  New windows 20 years ago are no longer new.  Two identical homes with a 10 year age difference might have obtained the exact same HERS score, but those intervening years will make a difference.  Now, who is going to establish the slope of that depreciation, I can't say.

At some point a home owner can look at the depreciated value of the old score, add in any other improvements, and decide that a new rating at some cost would be a good investment.

One of the difficult aspects of a "score" is the presumed accuracy of that number.  Just because the end result comes out of a computer doesn't mean it is accurate.  The list of assumptions from the internal equations to the data entered has been trying to match real results since auditing began, and they aren't there yet.  That means more assumptions and changes in how the score is generated are yet to come.

As for changes yet to come, which score counts? 


I appreciate all the responses and I think you are getting the message as to why this answer deserves some attention.  Steve Baden does not have any studies.  Appraisers and secondary mortgage market will want some facts going forward if we are going to be using the HERS Reports as the basis for measuring energy efficiency.

Facts speak for themselves and that's what we need!  Thank you for all the comments.

If there are no changes (mechanicals, leakage, etc...) a house rated a 75 5 years ago is still a 75 today (in theory). The only reason I say in theory is because they have tweaked a few algorithms so it might have moved a point or so - shoot see if anyone has any ratings done way back then & have them reopen them in the newer version - there's your answer.

The only other item I could see on why a score might change from the original new home to an older is when we cannot verify the insulation level (especially fiberglass) it becomes a grade 3 instead of a grade 1 which may have been verified before the drywall went up.


I understand "theory" but theory should be supported with fact.  The secondary mortgage market expects appraisers to support their numbers with fact and that includes reports we rely upon.  We really need a study that uses not only utility bills but a revisit to the HERS Rating 5 yrs out or more.  This will provide support to a market that the HERS Index is a true measure of EE beyond the initial new construction rating.

Well I will call BS - you do not need electrical bills et al (which Blasnik actually did below) as that only clouds the issue (though it can help in certain circumstances) - an appraisers job is to come up with a fair appraisal given all the facts based on the house in question, not how a homeowner used the utilities. How they maintained it, sure, but short selling a home because one was competing with a local airport as compared to a frugal person who liked dining by candle light & never owned a TV???

How do you rate a water heater - well for most you look at the usage sticker on the heater (or pull one up) - does that define exactly how much hot water a past individual actually used? No it simply relies on a set test to determine what an "average" person using said appliance can expect to pay. This also applies to cars MPG, ENERGY STAR appliances, a HERS score, etc... as they are all asset based ratings 

If you want a study to see how a HERS rating changes over 5 years, ask for people that know the original rating & still have the files to open them up in the newest version & see what it is today. Personally after 5 years it should be redone as it is very rare that they have left everything the same - you have cable or satellite TV repairman that just love screwing around with stuff, failure to maintain the shell or having mice invade might change it. Also one quickly overlooked item is maybe they switched from incandescent to CFL or LED.

As for supporting a market, I suggest looking at markets that have already added them - I have seen quite a few studies where they show increased & quicker sales because the information was there.

You might want to check out this study of homes in Houston that included tracking of actual energy use over time after construction for up to five years (see pages 33-34) among other things.


I am well aware of the study that was sponsored by Advanced Energy.  It does not verify the HERS Index.  I contacted Advanced Energy initially when I started this post.  The study does provide some good support for energy bills but if the HERS Index Report is going to be relied upon, let us do some factual studies to support the "theory".  Thanks to all that are responding to this post.  I think you see the problem the appraisal community is having defending this rating.

I guess I don't understand what you mean by factual studies -- I would think comparing actual energy use to projections from the ratings across many thousands of homes and then also looking over multiple years would be considered a factual study. What are you actually looking for?


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