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107 Acronyms & Initials for Home Energy Pros

Home Energy Alphabet Acronym Initials

Acronyms and initials (let’s call that AI, for short, not to be confused with the other AI, which stands for artificial intelligence, or AIA, which stands for American Institute of Architects) are part of the jargon of every field. Our field, whether you call it building science, green building, home performance, or something else, is no exception. So, a few years ago I started putting together a list that I now include in the manuals that we give out in our training classes (HERS rater and BPI Building Analyst).

I’m up to 107 total lines in my list, which our students find very helpful in sorting out all the jargon that’s new to them. When you first come into this field and start getting the barrage of ACH50, HVAC, COP, HDD, WRB, and more thrown at you, it’s good to have somewhere to look these things up.

Also, if two AI have the same definition, I included them on the same line. For example, SHR and SHF both refer to the same quantity, even though one uses the word fraction and the other ratio. When a single AI has two different definitions, however, I put them on separate lines. The only one I have like that right now is CO, which could stand for carbon monoxide or certificate of occupancy.

Anyway, I’m sure you’re dying to find out what RTFM stands for, so let’s get on with it. Below is a table of my top 50 acronyms and initials. If you want the full list, see my instructions below the table.

AI What it stands for URL
ACCA Air Conditioning Contractors of America
ACH50 Air Changes per Hour at 50 Pascals
AFUE Annualized Fuel Utilization Efficiency
AHRI Air Conditioning, Heating, and Refrigeration Institute
ASHRAE American Society of Heating Refrigerating & Air conditioning Engineers
BAS building airflow standard
BPI Building Performance Institute
BTU British Thermal Unit
CCF hundred cubic feet
CFA conditioned floor area
CFL compact fluorescent light
cfm50 cubic feet per minute at 50 Pascals
CO carbon monoxide
COP coefficient of performance
EER energy efficiency ratio
EF energy factor
EPS expanded polystyrene
ERV energy recovery ventilator
GSHP ground-source heat pump
HDD heating degree days
HERS home energy rating system
HPwES Home Performance with ENERGY STAR program
HRV heat recovery ventilator
HSPF heating season performance factor
HVAC heating, ventilating, and air conditioning
IAQ indoor air quality
ICC International Code Council
ICF insulated concrete form
IECC International Energy Conservation Code
LED light emitting diode
LEED Leadership in Energy & Environmental Design
MERV minimum efficiency reporting value
NAHB National Association of Home Builders
NZEH net zero energy home
OSB oriented strand board
PTAC packaged terminal air conditioner
QAD Quality Assurance Designee
RESNET Residential Energy Services Network
RH relative humidity
RTFM read the friendly manual
SEER seasonal energy efficiency ratio
sfbe square footage of building enclosure
SHF or SHR sensible heat fraction or sensible heat ratio
SHGC solar heat gain coefficient
SIP structural insulated panel
SPF spray polyurethane foam
SWAG scientific wild-ass guess
WRB weather resistive barrier or water resistant barrier
wrt with respect to
XPS extruded polystyrene

I apologize for not giving definitions and discussions of all of the AI above, but the purpose of this list is just for people to decode the letters when they hear or read them. Perhaps I’ll turn it into a full glossary some day.

Get the full list

If you’d like the expanded list of what is currently 107 acronyms and initials, go here:

Get the List!

You can choose to get it as either MS Excel spreadsheet or as a pdf file.


I hope you find this useful. If you’re relatively new to the field, this list can be quite handy. If you’ve been in the field for a while, you probably know all or most of what’s here, but maybe you have some others that you think I should add. Let me know.


Related Articles

HERS Lingo

Know Your Terms – Heat Pump Efficiency Ratings SEER & HSPF

Learn the Lingo – Air Conditioning Terminology & Tidbits



AI isn’t an acronym because if you tried to say it, someone might dial 911. To be an acronym, it’d have to make a nice word-like sound. Something like IMP (Insulation Manufacturers and Partners) or LUST (leaking underground storage tank), for example. (Only one of those is something I made up, btw.) AI isn’t an abbreviation either, which is usually a shortened version of a single word. And don’t get me started on contractions! No, AI is a set of initials, which is usually the word people should use when they call something an acronym.


Image of letters by tikitoy998 from, used under a Creative Commons license.

This Post Has 12 Comments

  1. Great List! 
    Great List! 
    I learned wrt as “with reference to” when using the two taps on a manometer channel. ‘respect’ doesn’t seem to have the same connotations. YMMV

  2. John N.: I
    John N.: I guess I picked up the ‘with respect to’ meaning from all the math and physics classes I took. In home energy world, though, you are correct that it seems most people use the word ‘reference’ instead of ‘respect.’ The meaning is the same in either case.

  3. I find that those who don’t
    I find that those who don’t RTFM it seems to generate a WTF, usually followed by a few !!’s, (which I don’t see in your short list) from others.

  4. Or As it relates to the
    Or As it relates to the effectiveness of the BS business in General we might Add: 

  5. Allison, I know you’re a
    Allison, I know you’re a southerner so I assume you have ADD because you forgot CDD

  6. Anthony H.
    Anthony H. (again): And of course, most people are probably aware that the F in RTFM can stand for something besides ‘friendly’ too. 
    Stan: Well, that one’s common enough and not really industry specific that I didn’t feel it was necessary to include it (although RTFM isn’t industry specific either). 
    pj: Well, I guess that depends on who’s doing the judging. 
    Bill S.: Ah, yes, I’m embarrassed to admit that it wasn’t even on my expanded list…until just now. I do remember considering it but I guess I didn’t include it because it’s not used all that much.

  7. John Straube refers to them
    John Straube refers to them as TLA’s (three letter acronyms) and FLA’s (four letter acronyms or* five).

  8. Here’s another one for the
    Here’s another one for the list: 
    HIRL – Home Innovation Research Labs. It is the re-branded version of NAHB Research Labs for their green certification program. One would probably pronounce it “hurl”, as in upchuck, etc?? Unintended consequences?

  9. Enough people use ELA when
    Enough people use ELA when they mean EqLA that ambiguities arise often. We use EfLA for the US or LBNL or Effective Leakage Area and EqLA for the Canadian or Equivalent Leakage Area. The fact that EqLA can be measured as a simple hole cut in a box makes it more useful in the field so it used a fair bit. As it is now, you have to guess from the author as what was intended and if the author is second guessing who the reader is, then they might already have converted to EfLA for example. Without correcting for test pressure and n value of a test we can say that: 
    EfLA = EqLA X 0.611 
    meaning EqLA is always a bigger value.  
    While we are at it, we can get dates sorted. US is month-day-year, Canada is day-month-year and Europe is often year-month-day which is the only one that sorts documents chronologically. To avoid the constant confusion with dates, we use year-month-day and certainly not year with two numbers only otherwise what date is 08-09-10 ? There are at least three possibilities but: 2009-08-10 should be clear to anyone and can be put into filenames whereas /or as a separator cannot.

  10. Recommend adding the National
    Recommend adding the National Air Duct Cleaners Assoication (NADCA) to your list. 

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