Blueprint Symbols: Floor Plan, Electrical, Plumbing, and HVAC

Blueprint symbols are the shorthand a designer uses so a plan sheet doesn’t have to spell everything out. A door is a line with an arc. An outlet is a small circle with two lines through it. A ceiling diffuser is a square with arrows. Learn the common ones and a sheet that looked like noise starts reading like a list of instructions.

One rule first, because it settles most arguments on site: the legend sheet in your plan set is the final word. There’s a national standard for these symbols, but it’s voluntary, and every architect and engineer draws a few of them their own way. The charts below cover what you’ll see most often. The legend tells you what this particular set means.

Start With the Legend Sheet

Every complete plan set has a sheet, or part of a sheet, that lists the symbols and abbreviations used in it. On architectural sets it’s usually near the front with the general notes. The trades often carry their own: the electrical legend sits on the first electrical sheet, the plumbing legend on the first plumbing sheet, and the mechanical legend on the first mechanical sheet.

The industry’s reference is the United States National CAD Standard, published by the National Institute of Building Sciences with the American Institute of Architects and the Construction Specifications Institute. It includes a standard symbols library and the rules for how sheets in a set are organized. Plenty of firms follow it closely. Plenty start from it and change things. That’s why the legend matters more than any chart, this one included.

Two habits save a lot of trouble:

• Keep the legend with the sheets you’re using. If you pull the electrical sheets out of the set for a crew, pull the electrical legend with them.
• Read abbreviations in context. The same two letters can mean different things on different sheets. There’s a short list of the usual troublemakers further down.

Floor Plan Symbols

The architectural floor plan is the sheet every trade starts from, so its symbols are worth knowing cold.

Symbol	What it looks like	What it means
Wall	Two parallel lines, often filled or hatched	Hatch or fill patterns usually separate new walls from existing ones and one material from another. Check the legend
Wall or partition tag	A small shape with a number or letter	Points to a wall type in the partition schedule, which gives the studs, layers and rating
Door	A straight line for the door leaf and a quarter-circle arc for the swing	The arc shows which way the door opens and which side it’s hinged on
Door tag	A circle, hexagon or box with a number, near the door	Points to the door schedule for size, type and hardware
Window	Thin parallel lines set into the wall	The window sits in the wall at that spot
Window tag	A shape with a letter or number near the window	Points to the window schedule for type and size
Stairs	Parallel lines for treads, an arrow, and a break line	The arrow is labeled UP or DN from the floor you’re looking at
Room tag	Room name with a number, often in a box	The room number ties to the finish schedule
Section marker	A circle split by a line, with an arrow or flag	Top number is the drawing number, bottom is the sheet it’s on. The arrow shows which way the section looks
Detail callout	A circle with a drawing and sheet number, tied to a boundary around the area	That area is drawn larger on the sheet named in the circle
Elevation marker	A circle or shape with one or more pointers	Points to an exterior or interior elevation and the sheet it’s on
Column grid	Letters in bubbles one way, numbers the other	Grid lines are how everyone on the job names a location: “at C-4”
North arrow	An arrow, often with an N	Orients the plan. Not always straight up the sheet
Revision cloud	A scalloped outline with a triangle and number	That area changed in the revision numbered in the triangle
Dashed lines	Short dashes	Usually something above or hidden: overhead cabinets, a soffit, a beam. The legend will say
Centerline	A long dash, short dash pattern, sometimes marked CL	The center of a wall, column, opening or fixture

The section, detail and elevation markers are the ones newer folks skip, and they’re the ones that send you to the right sheet. If a bubble reads 3 over A-501, the drawing you want is detail 3 on sheet A-501.

Electrical Symbols

Electrical plans are mostly small symbols scattered across a floor plan, with circuits drawn between them. Here are the ones you’ll see on nearly every set.

Symbol	What it looks like	What it means
Duplex receptacle	A small circle with two short parallel lines through it	A standard two-outlet receptacle
GFCI receptacle	The receptacle symbol labeled GFI or GFCI	Ground fault protected outlet. Kitchens, baths, garages, exterior
Weatherproof receptacle	Receptacle symbol labeled WP	Outlet with a weather-resistant cover
Special-purpose outlet	A receptacle symbol with a letter, number or note	A dedicated or higher-voltage outlet. The note or legend gives the details
Single-pole switch	The letter S	One switch controls the fixture
Three-way switch	S with a small 3 (S3)	Two switches control the same fixture, like at each end of a hall
Four-way switch	S with a small 4 (S4)	Used between two three-ways for a third switch location
Ceiling light	A circle, often with a letter or tag inside or beside it	The tag points to the light fixture schedule
Switch leg	A curved line, often dashed, from switch to fixtures	Shows which switch controls which lights. Not the wire route
Home run	A line ending in an arrow, labeled with circuit numbers	The circuit runs back to the panel named on the line
Panel	A rectangle, often filled, with a name like LP-1	Panelboard. The panel schedule lists every circuit
Smoke detector	Often a circle labeled SD or SMK	Smoke alarm. Check the legend, because SD can mean other things
Data or phone	Often a triangle	Low-voltage outlet for data or phone

Electrical sheets lean hard on schedules. The light fixture schedule, panel schedules and one-line diagram carry the detail the plan symbols can’t. If a symbol has a tag next to it, there’s a schedule somewhere in the set that explains it.

Plumbing Symbols

Plumbing plans use fixture outlines on the architectural background, plus pipe runs labeled by system.

Symbol or abbreviation	What it looks like	What it means
Fixtures	Outlines of the fixture, often tagged	Water closet (WC), lavatory (LAV), urinal (UR), shower (SH). Tags like P-1 point to the plumbing fixture schedule
CO	Small circle or symbol labeled CO	Cleanout. You’ll also see FCO (floor cleanout) and WCO (wall cleanout)
FD	A small square or circle labeled FD	Floor drain
HB	Symbol labeled HB	Hose bibb, the outdoor faucet
CW	A line labeled CW	Cold water
HW	A line labeled HW	Hot water. HWR or HWC is hot water return or recirculation
SAN or W	A heavier line labeled SAN, S or W	Sanitary or waste piping
V	Usually a dashed line labeled V	Vent piping
VTR	Note at the top of a vent	Vent through roof
Pipe size	A number with the inch mark next to a run	The pipe size for that run

Watch out for WH. On one set it’s a water heater. On another it’s a wall hydrant, and the water heater is WHR, EWH or GWH. It’s a small thing until someone orders the wrong one. The plumbing legend settles it.

Line styles for each system vary more in plumbing than in any other trade. One firm draws vent as short dashes, another as a long-short pattern. Read the legend before you trace a line across the sheet.

HVAC Symbols

Mechanical plans show ductwork, the air devices at the end of it, and the equipment feeding it.

Symbol	What it looks like	What it means
Supply diffuser	A square, often with diagonal lines or arrows	Ceiling supply. Arrows show the throw direction: four-way, three-way, two-way, one-way
Linear diffuser	A long narrow rectangle	Slot diffuser. The number of slots is in the tag or schedule
Return grille	A square or rectangle, often hatched or labeled RG or RA	Return air back to the unit
Exhaust grille	Labeled EG or EA	Exhaust air out of the building, as in restrooms
Air device tag	A tag with a type and a number	Type points to the diffuser schedule. The number is the airflow in CFM
Ductwork	Double lines with a size like 14×10	Rectangular duct, width by depth in inches. Round duct is marked with a diameter
Flex duct	A wavy or squiggly double line	Flexible duct, usually the last run to a diffuser
Airflow direction	Arrows on the duct, or toward/away symbols	Which way the air moves
Thermostat	Usually a T, often in a circle or hexagon	Thermostat or temperature sensor
Equipment tag	A label like RTU-1, AHU-1, EF-1	Rooftop unit, air handler, exhaust fan. The equipment schedule has the details

Supply, return and exhaust ducts are told apart by line style or hatching, and that’s set in the legend. On most mechanical sheets the numbers that matter are the duct sizes and the CFM on each device. Both get small fast.

Abbreviations That Trip People Up

Every set has an abbreviation list. These are the ones that cause the most second looks:

• TYP: typical. The note applies everywhere the same condition shows up, not just at that spot.
• SIM: similar. Close to the referenced detail, but not identical. Check what’s different.
• NTS: not to scale. Don’t measure it.
• AFF: above finished floor. Mounting heights for outlets, switches and fixtures are measured from here.
• NIC: not in contract. Shown for reference, but it’s somebody else’s work.
• EQ: equal. Space the items evenly.
• CL: usually centerline. On some floor plans it’s closet. Context tells you which.
• WH and SD: see above. Both have more than one meaning depending on the trade.

Symbols Have to Survive the Print

Here’s the part that doesn’t show up on symbol charts. Every symbol and tag on a plan was sized for the sheet it was drawn on. Print the set smaller and they all shrink with it.

An Arch D sheet printed on 11×17 comes out at about 46% of full size. A common CAD text height, 3/32 inch, ends up under a twentieth of an inch. Door tags, circuit numbers, CFM values and pipe sizes are often the smallest text on the sheet, and those are the numbers people need to read. 11×17 is a workable half size for walking a job and for the truck. For sheets dense with tags and schedules, keep a full-size set where the work is being laid out.

A few habits keep a printed set readable:

• Print the legend with every partial set. An electrical set without its legend is a set of guesses.
• Print schedules full size when a crew is working from them. The fixture, panel and diffuser schedules are dense, and they’re where the detail lives.
• Watch for color. Some designers use color in the PDF to separate systems or new from existing work. Printed in black and white, those can look the same. If the legend relies on color, order those sheets in color.
• Print at 100%. A set shrunk to “fit to page” changes the scale and the size of every symbol on it. Our guide to what to send your print shop covers how to set up the PDF.

Full-Size Sets, Legends Included

We print plan sets at 100% on the sheet size the title block calls for: full-size Arch C, Arch D and Arch E, plus 11×17 half-size copies for the field. Need the trade sheets as a field copy with the legend pulled along? Tell us, and we’ll build it that way. When color carries meaning, we print those sheets in color.

Upload at pblueprints.com, walk in at the Port Charlotte print room, or get it delivered to the job in Charlotte, Sarasota, DeSoto, or Lee counties. Most orders that reach us during business hours go out the same day.

Precision Blueprint Co. is a division of Creek Engineering.

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