4.Identify the approved piping materials for various water supply, drainage, and venting applications under the Massachusetts Uniform State Plumbing Code (248 CMR 10.00).
5.Apply the correct pipe sizing methodology for water distribution systems using the fixture-unit method and pressure-loss calculations.
6.Distinguish between required valve types, locations, and access requirements for water supply, gas piping, and drainage systems.
7.Understand the hierarchy of code references—MGL 142, 248 CMR, and NFPA 54/58—and navigate to the correct section when a code question arises.
8.Recognize common field installation errors and code traps related to piping supports, thermal expansion, and valve accessibility.
1.1 Scope and Regulatory Hierarchy
As a master plumber, you are responsible for work that complies with the Massachusetts Uniform State Plumbing Code (248 CMR 10.00–10.23, 2023), which adopts and amends the International Plumbing Code (IPC) framework. However, Massachusetts is a home-rule state with specific amendments. The exam expects you to know where the Massachusetts code deviates from the model code.
Key hierarchy:
MGL Chapter 142 establishes the licensing law and the Board of State Examiners of Plumbers and Gas Fitters.
248 CMR 10.00 is the plumbing code; 248 CMR 3.00, 4.00, 5.00, and 11.00 cover administrative procedures, licensing, and enforcement.
NFPA 54 (National Fuel Gas Code) and NFPA 58 (Liquefied Petroleum Gas Code) are adopted by reference for gas piping and appliances.
248 CMR 6.00 and 7.00 address gas fitting and oil burning equipment respectively.
For piping, valves, and controls, the primary content is in 248 CMR 10.10 (Materials) and 10.13 (Water Supply and Distribution). Drainage and vent piping materials appear in 10.15 and 10.16.
1.2 Approved Piping Materials
1.2.1 Water Supply Piping
The code permits the following materials for potable water supply, provided they meet applicable standards (ASTM, ANSI, NSF):
Copper tubing (Types K, L, M) — ASTM B88. Type M is permitted for above-ground water distribution but not for underground burial. Type K is required for underground and for all piping subject to external corrosion.
CPVC (chlorinated polyvinyl chloride) — ASTM D2846, for hot and cold water. Must be marked with the appropriate pressure rating and NSF 61 certification.
PEX (cross-linked polyethylene) — ASTM F876/F877. Must be installed with approved fittings (crimp, clamp, or expansion). PEX cannot be installed within 6 inches of a vented appliance flue or within 12 inches of a gas water heater vent connector.
Galvanized steel — ASTM A53, permitted but rarely used in new work due to corrosion and scale buildup. Threaded joints only.
Stainless steel — permitted for special applications.
Prohibited: Lead piping, galvanized piping for water that is not protected against corrosion, and any material that imparts taste, odor, or toxicity to the water.
1.2.2 Drainage and Vent Piping
Cast iron (service and extra-heavy) — ASTM A74, for soil and waste stacks.
PVC (polyvinyl chloride) — ASTM D2665 for DWV; ASTM F891 for cellular core. PVC is permitted for drainage and venting above and below grade.
ABS (acrylonitrile butadiene styrene) — ASTM D2661, permitted but must be joined with solvent cement approved for ABS.
Copper — for drainage, limited to 3 inches or less in diameter and must be Type DWV or heavier.
Lead — prohibited for drainage and venting.
Exam trap: Do not confuse the material standards for water piping (NSF 61) with drainage piping (no NSF requirement). Also, PVC for DWV is not the same as PVC for pressure water—the cell class and schedule differ.
1.3 Pipe Sizing — Water Supply
1.3.1 Fixture Unit Method
Water supply sizing is based on fixture units (w.s.f.u.) assigned to each fixture type. The code provides a table (similar to IPC Table E103.3) that assigns values for private and public use. For example:
Water closet (tank): 2.2 w.s.f.u. private, 3.0 public
Lavatory: 1.0 w.s.f.u.
Shower: 2.0 w.s.f.u.
Sink (kitchen): 1.5 w.s.f.u.
Washing machine: 2.0 w.s.f.u.
The total w.s.f.u. is converted to a required flow rate (gallons per minute) using a demand curve. For a typical residence, the demand curve is nonlinear: 10 w.s.f.u. ≈ 6 gpm; 20 w.s.f.u. ≈ 9 gpm; 50 w.s.f.u. ≈ 15 gpm.
1.3.2 Velocity and Pressure Loss
The code limits water velocity in piping to 8 feet per second to prevent erosion and water hammer. The master plumber must calculate pressure loss due to friction using the Hazen-Williams formula:
Pressure drop (psi per 100 ft) = 0.2083 × (100/C)^1.852 × (Q^1.852 / d^4.8655)
Where:
C = roughness coefficient (140 for copper and PEX, 100 for steel)
Q = flow rate in gpm
d = inside diameter in inches
Available pressure is the difference between the supply pressure (typically 40–60 psi municipal) and the minimum required fixture pressure (8 psi for most fixtures, 10 psi for flushometer valves). Subtract elevation loss (0.433 psi per foot of rise) and meter/valve losses.
Exam trap: The code requires the minimum water supply size to a building to be ¾ inch, regardless of the calculated demand.
1.4 Valves — Types and Locations
1.4.1 Water Supply Valves
The code mandates the following valves:
Main shutoff valve: A full-open gate or ball valve on the water service entrance, inside the building, accessible, and within 5 feet of the point of entry.
Individual fixture shutoffs: Required at each fixture supply (angle stops) for maintenance.
Hose bibbs: Must be equipped with a vacuum breaker or backflow preventer, and each hose bibb must have an accessible shutoff valve.
Pressure-reducing valve (PRV): Required when the static water pressure exceeds 80 psi. The PRV must be installed with a bypass and a strainer, and be accessible for servicing.
Backflow prevention: Reduced-pressure principle assembly (RP) for health hazards; double-check valve for non-health hazards. These must be tested annually and installed with test cocks.
1.4.2 Drainage Valves
Cleanouts: Required at the base of every soil stack, at every horizontal drain change of direction greater than 45°, and at intervals not exceeding 100 feet for pipes 4 inches or less, and 150 feet for larger pipes.
Backwater valves: Required on building sewers where the elevation of the lowest fixture is below the elevation of the next upstream manhole cover.
1.4.3 Gas Piping Valves (NFPA 54)
Gas shutoff valve at the meter outlet.
Individual appliance shutoff valves within 6 feet of the appliance, upstream of the connector.
Sediment trap (drip leg) required at every appliance that does not have an integral trap, installed at the point of connection.
Exam trap: The code requires a union downstream of the gas shutoff valve to allow appliance removal without disturbing the piping.
1.5 Piping Supports and Installation
1.5.1 Support Spacing
The code provides a table of maximum horizontal support spacing based on pipe material and size. Key values:
Copper tubing (1¼ inch and smaller): 6 feet
Copper tubing (1½ inch and larger): 10 feet
Galvanized steel (1¼ inch and smaller): 8 feet
Galvanized steel (1½ inch and larger): 12 feet
PVC/CPVC (all sizes): 4 feet for horizontal, 8 feet for vertical
Cast iron: 5 feet for horizontal, 10 feet for vertical
Vertical pipes must be supported at each floor level, but not more than 15 feet apart for metal piping and 10 feet for plastic.
1.5.2 Thermal Expansion
The code requires that thermal expansion be accommodated in all hot water systems. This means:
A thermal expansion tank (or a listed expansion device) must be installed on the cold water supply line upstream of the water heater when a check valve or PRV is present.
The expansion tank must be sized to the water heater capacity and the system pressure. A general rule: 2 gallons of expansion capacity per 50-gallon water heater at 80 psi.
Exam trap: The expansion tank is not required if the system has an open vent or a relief valve that opens at the system pressure—but in a closed municipal system, the PRV alone does not relieve thermal expansion.
1.6 Controls and Safety Devices
1.6.1 Temperature and Pressure Relief Valves
Every water heater must have a combination temperature and pressure (T&P) relief valve:
Set to open at 150 psi or 210°F, whichever occurs first.
The T&P valve must be installed in the upper 6 inches of the tank, with the sensing element in the top 6 inches of water.
The discharge pipe must be sized to the valve outlet, must not be threaded at the end, and must terminate within 6 inches of the floor, with no valve between the T&P and the discharge point.
1.6.2 Water Heater Controls
Thermostat: Must be set to a maximum of 140°F for storage tanks unless a mixing valve is installed for scald protection.
Mixing valves: Required at point-of-use for public facilities (schools, daycares, nursing homes) to limit delivery temperature to 120°F.
1.6.3 Gas Appliance Controls (NFPA 54)
Gas pressure regulators: Required when the supply pressure exceeds the appliance rating. The regulator must be vented to the outside if the gas is undiluted LP.
High-temperature limit controls: Required on all gas-fired water heaters.
Flame rollout switches and draft hoods are required for atmospheric burners.
1.7 Code Navigation — Where to Find It
Concept
Code Reference
Piping materials (water)
248 CMR 10.10; IPC Chapter 6
Piping materials (DWV)
248 CMR 10.15; IPC Chapter 7
Water supply sizing
248 CMR 10.13; IPC Appendix E
Valve requirements
248 CMR 10.13.4; IPC 606
Backflow prevention
248 CMR 10.13.6; IPC 608
Cleanouts and backwater valves
248 CMR 10.15; IPC 708, 715
Gas piping and valves
NFPA 54 Chapters 5, 6, 7
T&P relief valves
248 CMR 10.13; IPC 504
Piping supports
248 CMR 10.10; IPC 308
Thermal expansion
248 CMR 10.13; IPC 607
Water heater controls
248 CMR 10.13; IPC 501–504
Pressure-reducing valves
248 CMR 10.13; IPC 606.5
1.8 Practical Field Points for the Master Plumber
109.Permit and inspection responsibility: As the master plumber, you must ensure that all piping, valves, and controls are installed per the approved plans. The code requires that the installing plumber be present for the final inspection and that all test results (e.g., water pressure test at 100 psi for 30 minutes) be documented.
110.Pressure testing: Before concealing piping, the system must be tested at 1.5 times the working pressure, but not less than 100 psi, for 30 minutes. For gas piping, the test is at 10 psi for 30 minutes with no drop, using a manometer.
111.Cross-connection control: You are responsible for identifying potential cross-connections. A hose bibb without a vacuum breaker is a code violation and a public health hazard. Install an atmospheric vacuum breaker (AVB) on every hose bibb.
112.Accessibility: Valves must be accessible. Do not install shutoff valves behind built-in appliances without an access panel. The code requires that all valves be installed so that they can be operated without removing any permanent construction.
113.Material compatibility: Do not mix copper and galvanized steel in the same water system without a dielectric union. Electrolysis will cause premature failure.
1.9 Common Exam Traps
Trap 1: Confusing the water supply fixture unit (w.s.f.u.) with the drainage fixture unit (d.f.u.). They are not equal. A water closet is 2.2 w.s.f.u. but 3–6 d.f.u. depending on the fixture.
Trap 2: Assuming that a PRV set at 80 psi eliminates the need for a thermal expansion tank. It does not—the PRV is a one-way valve.
Trap 3: Forgetting that the T&P relief valve discharge pipe must not be connected to the drainage system. It must terminate by gravity to a safe point of discharge.
Trap 4: Using schedule 40 PVC for a water supply line. PVC is not approved for hot water or potable water supply in Massachusetts; use CPVC or PEX.
Trap 5: Sizing gas piping by the same method as water piping. Gas piping uses the longest run method with a specific gravity of 0.60 for natural gas, and the table is based on pressure drop of 0.3 inch water column.
Trap 6: Installing a valve on the discharge side of a T&P valve or a backflow preventer. Both are prohibited by code.
Trap 7: Forgetting that the main shutoff valve must be a full-open type (gate or ball), not a globe valve, which restricts flow.
1.10 Summary
The piping, valves, and controls chapter of the Massachusetts Master Plumber exam requires you to integrate material standards, sizing calculations, and code-mandated safety devices. The most heavily tested areas are:
Approved materials and their standards
Water supply sizing using fixture units and pressure loss
Valve type and location requirements
Thermal expansion and T&P relief valve installation
Gas piping shutoff and sediment trap requirements
As a master plumber, you are not merely an installer—you are the responsible licensed professional who must ensure code compliance, public safety, and system performance. The exam will test your ability to make field decisions based on code logic, not memorized trivia. Always ask: "What does the code intend to protect?" The answer is usually public health, safety, and property protection.
