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Acronyms, Abbreviations & Glossary Of Common Terms

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This thread was originally posted in the other place, and is a team effort to collect together as many acronyms and abbreviations used in the building trade as we could.

If you know of any abbreviations missing, or think there should be a correction to the list, then post them as a reply to this topic and one of the moderators can edit the original list to keep it all up together.


AAV = Air Admittance Valve. (Sometimes referred to as a Durgo Valve.)
AAV (alternative) = Automatic Air Vent.

ACH = Air Change [per] Hour

AIUI = "As I understand It".

AONB = Area [of] Outstanding Natural Beauty

Article 4 Direction = Removes Permitted Development (PD) rights. (See: http://www.brighton-...cle-4-direction )

ASHP = Air Source Heat Pump (And see also: http://www.planningp...ects/heatpumps/ )

BC / BCO / BI = Building Control / Building Control Officer / Building Inspector (Often prefixed with LA = Local Authority, as in LABCO.)

BR = Building Regulations (Regs)

CIL = Community Infrastructure Levy (= a charge levied by a LA based on the sq.m of a property. Note: self-builds are exempt.)

CO = Conservation Officer. (Now often designated: Heritage Officers. Specialized - although often not particularly qualified - planning officers working in a local authority Conservation/Heritage department. Have the power to over-rule BC where the Regs are concerned if a proposal is considered likely to impact on the "historic character" of a building, whether Listed or not, or in a Conservation Area.)

{Listed Building, see: http://www.planningp...ing_consent.pdf }

{Conservation Area, see: http://www.planningp...ns/conservation }

CU = Consumer Unit

CCU = Cooker Connection Unit

CWS = Cold Water Storage [tank]. (Large plastic tank often in attic.)

CYL Stat = hot water cylinder thermostat for control of DHW temperature.

DeltaT = ΔT (Greek symbol Δ =delta in Greek alphabet) Temperature difference. (In the building context usually referring to the difference in temperature across a wall when discussing the effectiveness of insulation.)

DG = Double Glazing (Sometimes referred to in shorthand as 2g = double glazed; 3g = triple glazed. Also expressed as 'd/g')


DCW = Domestic Cold Water

DHW = Domestic Hot Water


DNO = Distribution Network Operator (electricity supply)

DPC = Damp Proof Course

DPM = Damp Proof Membrane

EA = Environment Agency

EDPM = Roofing membrane. (EPDM rubber (ethylene propylene diene monomer (M-class) rubber), a type of synthetic rubber,)

EPC = Energy Performance Certificate (See: https://www.gov.uk/b...ce-certificates )

EPS = Expanded Polystyrene Insulation


EV - Expansion Vessel

EWI = External Wall Insulation

F&E = Feed and Expansion tank. (Small plastic tank often found in attic alongside CWS.)

FCU = Fused Connection Unit

FWIW = "for what its worth". (As in: "That's my opinion FWIW.")

FYI = For Your Information. (Now often seen in formal letters since they took the form of emails, and especially in the header of an email forwarded to keep someone "in the loop".)

GCN = Great Crested Newt

GSHP - Ground Source Heat Pump

HC or VHC = heat capacity/volumetric heat capacity

ICF= Insulated Concrete Formwork

IGU = Insulated Glazed Unit (industry term for double or triple glazing)

IMHO = "in my honest opinion." (Alternative: "in my humble opinion.")

IIRC = "If I remember correctly."

IWI = Internal Wall Insulation

KISS = Keep It Simple Stupid. (Usually expressed as: "Stick to the KISS principle.")

LA = Local Authority

LBC = Listed Building Consent. (Needed to carry out work on any Listed building, whether domestic or commercial, privately or publicly owned, which is protected by law because of its historic significance, whether by age or architectural importance attested to by English Heritage.) (See also: Listed Building, above.)

LPA = Local Planning Authority

LPG = Liquefied Petroleum Gas


M&E = Mechanical and Electrical

MCB = Miniature Circuit Breaker

MDPE = Medium-density polyethylene also referred to as Alkathene. Pipe used to carry mains water and gas, usually buried underground.

MI = Manufacturers Instructions

MVHR = Mechanical Ventilation [with] Heat Recovery.

NPPF = National Planning Policy Framework

OEM = Original Equipment Manufacturer

OLIVE = Compressible copper ring accompanying threaded plumbing fittings that compresses around the pipe when the fitting is tightened to form a watertight seal. Often reinforced with PTFE tape [see below].

OSB = Orientated strand board

Party wall = An internal wall common to two properties. (Not always a contentious issue, but see: http://www.planningp...on/partywallact )

PDR = Permitted Development Rights. (Sometimes just 'PD'. See: http://www.planningp...ssion/permitted )

PGM room stat = Programmable room thermostat: selects both operating times and temperatures.

PI = Professional Indemnity (Insurance)

PINS = Planning Inspectorate

PME = Protective multiple earthing

PIR = Rigid Polyisocyanurate Insulation

PoE (or POE) = Power over Ethernet. Enables power to be provided to the device (phone or a network camera) using the same cable as that used for network connection.

PRV = Pressure Relief Valve


PRedV - Pressure Reducing Valve  


PHE - Plate Heat Exchanger


PTFE (tape) = (polytetrafluoroethylene) Tape used to seal threads and joints (e.g. around olives in compressions fittings) in plumbing.  Also known as Teflon tape outside the UK

PUR = Rigid Polyurethane Insulation


PV = Photovoltaics e.g. Roof Solar panels

R-value = Thermal resistance [insulation] (the higher the better)

RCD = Residual Current Device

RCBO = Residual Current circuit Breaker with Overcurrent protection

RDF = Refuse Derived Fuel

RTFM = Read The Flipping Manual. (The polite version; the less inhibited version is usually expressed with the 'F' meaning what you think it means.)

SAP = Standard Assessment Procedure (See: https://www.gov.uk/s...sment-procedure ) (See also: https://www.bre.co.u...P-2012_9-92.pdf ) ( https://www.gov.uk/g...t_file_2012.pdf )



SE = Structural Engineer

SEPA = Scottish Environmental Protection Agency

SFCU = Switched Fused Connection Unit

SHC = Specific Heat Capacity (heat is another word for energy, don't confuse with temperature)

SIPs = Structural Insulated Panels

SSSI = Site of Special Scientific Interest

Stat = Thermostat. (Room stat = wall mounted thermostat/central heating control.)



SVP = soil vent pipe.

SWA = Steel Wire Armoured (cable)

SWMBO = She Who Must Be Obeyed (Attributed to "Rumpole of The [Old] Bailey", who used the phrase when referring to his wife, but actually from Rider Haggard's "She": https://www.youtube....h?v=bS5YmETSVCI )

TAF = Temporary Amphibian Fence

TBH = "to be honest" (As in: "TBH I don't know.")

TBF= "to be fair" (As in: "TBF to the builder, he hadn't a clue.)

T&E = Twin and Earth (cable)


TF = Timber Frame (form of house construction)

T&G = Tongue and groove. (Often given in lower-case: t&g.)

T&PV = Temperature & Pressure [relief] Valve

TS = Thermal Store

UFH = Under Floor Heating. (Also expressed as 'Underfloor Heating' but usually still given as UFH.)

U-value = Rate of transfer of heat [insulation] (get it as low as possible, below 0.15 if you can)

UVC = Unvented Cylinder

VCL = Vapour Control Layer

WUFI = "Wärme und Feuchte instationär" - Heat and Moisture transfer analysis

XPS = Extruded Polystyrene Insulation

ZV = Zone valve, motorised or other. (Directs heating medium to wherever needed according to programmed requirements.)



L x W x H = Length times width times height. (But note that when giving dimensions for windows and doors ALWAYS follow the convention of width first, following by the height.)

J = joule (not Joule)

W = watt

h = hour

s= second

k = kilo (thousand)

kW = kilowatt

kWh = kilowatt hour

kWp = kilowatt peak (Solar installations - literally peak output.)

m = metre (not meter)

m2 = square metre (not metre squared)

t = time

T = temperature

°C = Celsius or Centigrade

K = kelvin (not °K or degrees Kelvin)

k or k often means conductivity

R = resistivity

U = 1/R

g = gram

kg = kilogram (the odd SI unit, use it)

J/(kg.K) = J/(kg.K) = J.kg-1.K-1

W/(m2.K) = W/m2.K = W.m-2.K-1

f(x) = function of x. (Common usage in thermal and stress calculations as well as statistics.)

e = Exponent (1+1/1!+1/2!+1/3!+1/4!...) how things heat up and cool down, how fast things grow,

π = pi ratio of a circles diameter to its circumference


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9 hours ago, ProDave said:

m2 = square metre (not metre squared)

I think this is the wrong way around (and I think I may have posted it originally too)

Square meter is shape dependant, e.g. a rectangle of 1 m length by 1 m width.

A metre square is not shape dependant, e.g. the surface area of the Cornwall (as it is a really odd shape) 3.563824e+9m²

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  • 6 months later...

As requested in a thread about battery storage of renewable generation:


DoD -- depth of discharge (essentially the opposite of state of charge)

SoH -- state of health (a percentage of how much charge it can hold, compared with the as-new spec) 

Wh -- Watt-hour (a measure of energy)

BMS -- battery management system

LiFePO4 -- lithium iron phosphate (a rechargeable battery chemistry)

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EDPM → EPDM  Noticed that because I often make the same mistake. It seems quite common for some reason.


R = resistance (not resistivity).


Is it worth a note that mm² is (mm)² (not m(m²)) and that when people talk about 1, 2.5, 6 or whatever mm cable they usually mean mm² (i.e, cross-sectional area, not diameter)? There was a time when I was confused about that.

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  • 3 weeks later...

There's a lot of confusion in the world about kilowatts and kilowatt hours. Here's an attempt at an explanation.


The SI unit of energy is the joule (symbol J). It's quite small.


Power is the rate at which energy is generated, moved around or used up. The unit is the watt (symbol W). One watt is one joule per second (1 W = 1 J/s). Because the joule is quite small the watt is also not large. It's typically used for relatively low-power devices like lights.


The watt is a rate in much the same way that the knot is a rate (1 knot = 1 nautical mile/hour). Talking about watts/hour is about as likely to be wrong as talking about knots/hour (i.e., they're not normally used but could be meaningful in a few odd cases: watts/hour for the output of a PV factory, knots/hour for the acceleration of a supertanker, perhaps).


For things like heating the kilowatt (kW) is typically used. 1 kW = 1000 W = 1000 J/s.


IMHO, there'd be less confusion if we measured quantities of energy in joules and its multiples. E.g., it'd be better if electricity bills were in MJ (megajoules).


But we don't. Instead it's common to use the watt-hour (Wh) and its multiples. One watt-hour is the amount of energy transformed by a power of one watt for one hour. 1 W is 1 J/s and one hour is 3600 seconds so 1 Wh = 1 J/s × 3600 s = 3600 J as the seconds cancel.


One kilowatt hour (1 kWh) is one kilowatt for one hour, or 1 watt for 1000 hours or whatever combination multiples to the same amount. 1 kWh = 1000 J/s × 3600 s = 3'600'000 J = 3.6 MJ.

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On 12/10/2018 at 22:57, Ed Davies said:

EDPM → EPDM  Noticed that because I often make the same mistake. It seems quite common for some reason.


R = resistance (not resistivity).


Is it worth a note that mm² is (mm)² (not m(m²)) and that when people talk about 1, 2.5, 6 or whatever mm cable they usually mean mm² (i.e, cross-sectional area, not diameter)? There was a time when I was confused about that.

You have to be careful with cable size in DC applications as they can sometimes refer to the diameter of a cable including the insulation. Shouldn't be an issue in our applications unless off grid.

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BTU = British Thermal Unit, so called because it's mostly used by Americans these days.


Strictly, it's a unit of energy (not power). There are various definitions but 1 BTU ~= 1055 joules.


Often, though, it's used as a unit of power with an implicit /hour bit omitted. 1000 BTU/hour = 1'055'000 J / 3600 seconds ~= 293 watts ~= 300 W.

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  • 3 months later...
  • 3 months later...

Capitalization of units: it usually doesn't matter too much in practice but there is a standard which is followed by all scientific journals, etc, which is worth following to avoid the small possibility of confusion. Most accessibly:  BIPM SI Brochure and Wikipedia.   


For capitalization in English and French the rules are pretty simple:


1) Names of units are written in lower case except in situations where any word would be capitalized (beginnings of sentences, titles, etc) even if the unit is named after a person. So meter, gram, watt, joule, pascal and so on.


2) Similarly, when spelled out, the prefixes for multiples and submultiples are written in lower case: mega, kilo, deca, milli, nano.


3) Symbols for units are written in lower case if they're not named after people (m (meter), g (gram), s (second), h (hour)) but initial capped if they're named after somebody (W (James Watt), J (James Prescott Joule), Pa (Blaise Pascal)).


4) The prefix symbols are lower case for prefixes up to and including a thousand (p (pico), n (nano), μ (micro), m (milli), c (centi), h (hecto), k (kilo)) but initial capped for multiples of a million and larger (M (mega), G (giga), T (tera).


So the symbol for kilowatt-hour is kWh (or kW·h). All other capitalizations are non-standard.


Some odd cases:


It's a “degree Celsius”. The unit is the degree; “Celsius” here is not a unit name but the name of the scale (so a proper noun which, following the normal rules, is capitalized) being used adjectivally to say what sort of degree it is. But a kelvin is a unit so it's 300 K or 300 kelvin, not 300 °K or 300 degrees Kelvin.


The symbol for the litre is formally “l” (lower case letter el) but many people and some national standards prefer to use uppercase “L” to avoid confusion of the letter with the digit one.


I don't know what the appropriate symbol capitalization for the prefix kibi (x 1024) is, whether it's ki or Ki. I've seen both in use.

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5 hours ago, Ed Davies said:

Some odd cases:


It's a “degree Celsius”. The unit is the degree; “Celsius” here is not a unit name but the name of the scale

And there is the odd quirt that C is used for coulomb (named after Charles-Augustin de Coulomb) and is an amp.second, or just to make matter even worse, a farad.volt if talking about capacitors.  The sign for farad (named after Michael Faraday) is F, just to confuse with the Fahrenheit scale.

Thank goodness for the ° sign (which is Alt + 248, or Alt + 0176 on a PC).


Now who wants to explain ' and " with regards to time, distance and angles.

And Prime Numbers, or should that be primes.



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  • 1 year later...
49 minutes ago, SteamyTea said:

Just noticed a new abbreviation creeping in:


TS = Toolstation

TS = Thermal Store.


Not that anyone really knows what a thermal store is.


Can you think of a sentence where the two abbreviations are interchangeable?

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On 17/11/2020 at 16:36, joe90 said:

“Do TS sell TS,s ? ?


45 minutes ago, SteamyTea said:

Spotted another one (I really need to get out)


PHE = Plate Heat Exchanger

PHE = Public Health England


Bet you can't


"PHE demands are such that things get heated".

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