NASCLA Mechanical and Plumbing Systems guide

What the bulletin says, and what it leaves out

PSI's Candidate Information Bulletin (updated 7 Jul 2026) gives the area name and its count of 6, with no topic list. The topics below are our reading of the area name and the reference list.

The book to open

Mechanical and Electrical Systems for Construction Managers (4th edition, 2024) is the listed title that names this subject. Tab its index and its HVAC, plumbing and fire protection topics. Electrical Systems, a separate 3-question area, draws on the same title, so one book covers both. For where systems sit in the building code, use the International Building Code you bring.

Topics to cover

• HVAC. Packaged rooftop units, split systems, variable refrigerant flow and central plants. Supply, return and outdoor air. Cooling capacity in tons.
• Testing and startup. Testing, adjusting and balancing (TAB) sets air and water flows to design values. Commissioning checks that systems work together as the owner needs.
• Water supply. Meters, backflow prevention, pressure lost with height.
• Drainage, waste and vent (DWV). Traps hold a water seal against sewer gas; vents protect the seals and let drains flow; drain lines slope toward the sewer.
• Cross-connections. Any link between drinking water and a possible contaminant, stopped with air gaps or backflow preventers.
• Testing before cover-up. Water piping is pressure tested and DWV piping is tested before walls and ceilings close.
• Fire protection. Wet-pipe, dry-pipe, preaction and deluge sprinkler systems, and standpipes.
• Coordination and sequence. Ducts, drains, sprinkler mains and conduit compete for the same ceiling space. Underground plumbing goes in before the slab, rough-in before walls close, trim after finishes.

Constants worth knowing

• 1 ton of cooling = 12,000 Btu per hour. A ton here is a rate of heat removal, not a weight.
• Sensible heat in Btu per hour = 1.08 x cfm x temperature difference in degrees F, for standard air.
• A foot of water height is about 0.433 psi. Turned around, 1 psi lifts water about 2.31 ft. Check: 1 / 0.433 = 2.31.

Worked examples

All numbers are invented. Each is worked two ways.

Tons of cooling. A cooling load is 180,000 Btu per hour. Tons = 180,000 / 12,000 = 15 tons. Check: 15 x 12,000 = 180,000.

Heating coil output. An air handler moves 1,500 cfm with a 25 degree F rise across a coil. Heat = 1.08 x 1,500 x 25 = 40,500 Btu per hour. Check: 1,500 x 25 = 37,500, and 37,500 x 1.08 = 40,500.

Pressure at a high fixture. Pressure at the meter is 60 psi and the highest fixture is 35 ft above it. Static loss = 35 x 0.433 = 15.16 psi, leaving about 44.8 psi before friction losses. Check: 30 x 0.433 = 12.99 and 5 x 0.433 = 2.17, total 15.16; 60 minus 15.16 is 44.84.

Drain fall. A 36 ft horizontal drain is laid at 1/4 in. per foot, the slope the project sets for that pipe. Fall = 36 x 0.25 = 9 in. Check: 9 / 36 = 0.25 in. per foot. The required slope for a given pipe size comes from the plumbing code, so take it from the question or the documents.

Common mix-ups

• Vents do not exist to let sewer gas into the room. They protect trap seals and carry gases out through the roof.
• Gravity drains get priority in coordination. Their slope is fixed. A sprinkler line or duct can usually offset around them.
• Tons are a rate. 15 tons is 180,000 Btu per hour, not 30,000 lb.
• Test before you cover. Closing a wall over untested pipe is the costly mistake the question is usually pointing at.

How to practice

Learn the three constants until you can use them without looking, then work a few conversions each study day. Read the book's sections on coordination and sequencing and write the order of work for one floor of a building you know. The NASCLA study guide puts this area in week 7 with the other smaller trade areas; see also General Requirements for closeout, where TAB and commissioning reports end up.

Practice it

Take the free 10-question check and see your score by subject area in minutes. It needs no signup and explains every answer.

The NASCLA Commercial course has a lesson for each of the 12 subject areas that shows which listed reference to open and how to apply it, original practice questions with every answer worked, and four timed practice exams of 115 questions on a 330-minute clock. Your scores come back by subject area, so you know where the next study hour goes. See the course.

Not affiliated with or endorsed by NASCLA or PSI. NASCLA and PSI are named only to identify the exam and its test vendor. Book titles are named only to identify them.

Sources

Show the list

• PSI Candidate Information Bulletin 1458, content outline and reference list, updated 7 Jul 2026. Retrieved 5 Nov 2026.