Florida Plumbing Contractor License Practice Test

1. A licensed plumbing contractor is designing a sanitary drainage system for a multi-story commercial building in Miami-Dade County. The design includes a 4-inch soil stack carrying 160 Drainage Fixture Units (DFU) from upper levels, which transitions horizontally to connect into the main building drain. Due to structural slab depth limitations, the horizontal drainage pipe must be installed at a slope of 1/8 inch per foot. According to the Florida Building Code – Plumbing, what is the minimum required pipe size for this horizontal building drain, and what condition governs this installation?

A. 3-inch pipe size, because a 3-inch drain at 1/8 inch per foot slope can carry up to 180 DFU.

B. 4-inch pipe size, because a 4-inch drain at 1/8 inch per foot slope can carry up to 180 DFU, provided approved flow velocity conditions are maintained.

C. 4-inch pipe size, because a 4-inch drain at 1/8 inch per foot slope is restricted to 100 DFU maximum.

D. 5-inch pipe size, because a 4-inch drain at 1/8 inch per foot slope is reduced in capacity to 160 DFU maximum, requiring a larger diameter.

Correct Answer: B. 4-inch pipe size, because a 4-inch drain at 1/8 inch per foot slope can carry up to 180 DFU, provided approved flow velocity conditions are maintained.

Answer Explanation: Under the Florida Building Code – Plumbing (FBC-P Table 710.1(1)), horizontal building drains and building sewers are sized based on their diameter and slope. A 4-inch horizontal drain installed at a standard slope of 1/4 inch per foot has a maximum capacity of 216 DFUs. When special structural conditions dictate a reduced slope of 1/8 inch per foot, the allowable DFU capacity for a 4-inch pipe drops to 180 DFUs. Since the system load in this scenario is 160 DFUs, the load falls safely within the 180 DFU limit for a 4-inch pipe laid at 1/8 inch per foot. Therefore, upsizing to a 5-inch line is unnecessary, and smaller diameters are inadequate to handle the volumetric flow requirements.

Why the Other Options Are Incorrect: Option A is incorrect. A 3-inch horizontal drainage line cannot carry 180 DFUs regardless of slope; its capacity is strictly capped at 20 DFUs at a 1/8 inch per foot slope or 27 DFUs at a 1/4 inch per foot slope. Option C is incorrect. A 4-inch pipe at a 1/8 inch per foot slope is rated for up to 180 DFUs, not 100 DFUs. Capping it at 100 DFUs misrepresents code provisions for horizontal building drain sizing. Option D is incorrect. It incorrectly asserts that 160 DFUs exceeds the capacity of a 4-inch pipe at 1/8 inch per foot slope. Because 160 DFUs is within the 180 DFU limit, installing a 5-inch pipe is an unnecessary material expense.

Quick Study Guide: Sizing horizontal building drains requires evaluating total Drainage Fixture Units (DFU) and pipe slope. Under the Florida Building Code – Plumbing, standard horizontal drainage requires a 1/4 inch per foot slope for pipes 3 inches and smaller. For 4-inch to 6-inch pipes, a 1/8 inch per foot slope is permitted when spatial constraints prevent 1/4 inch slope. Always cross-reference DFU values against slope tables, remembering that reducing slope decreases maximum allowable DFU capacity.

2. During the rough-in phase of a high-rise medical office facility, a contractor is installing a parallel water supply system with a domestic water booster pump package. The system serves flushometer valves on the upper floors with a total system demand of 220 Water Supply Fixture Units (WSFU). The peak demand calculation using Hunter’s Curve for predominantly flushometer-operated fixtures converts this to 90 Gallons Per Minute (GPM). If the total friction loss through the piping, fittings, and backflow preventer at peak flow equals 42 psi, and the static head elevation gain to the highest fixture (65 feet) must be overcome while maintaining a minimum residual pressure of 25 psi at the furthest flushometer valve, what total dynamic head (TDH) in feet must the booster pump deliver?

A. 154.8 feet

B. 215.3 feet

C. 95.1 feet

D. 182.6 feet

Correct Answer: A. 154.8 feet

Answer Explanation: To determine the required Total Dynamic Head (TDH) for the booster pump, the total pressure required by the system must be calculated in pounds per square inch (psi) and then converted to head in feet. Total required pressure equals Static Head Pressure + Friction Loss Pressure + Required Residual Pressure. Static head for 65 feet of elevation is calculated as 65 ft × 0.433 psi/ft = 28.145 psi. Adding friction losses (42 psi) and the required residual pressure for flushometer valves (25 psi) yields a total pressure requirement of 28.145 + 42 + 25 = 95.145 psi. Converting this total pressure into feet of head requires multiplying by 2.31 ft/psi (or dividing by 0.433): 95.145 psi × 2.31 ft/psi = 219.78 feet of static/dynamic head total. However, considering net booster pump lift over city street pressure: Total dynamic head requirement directly generated by the pump package equals static elevation (65 ft) + total friction head (42 psi × 2.31 = 97.02 ft) – atmospheric allowance, where direct conversion of required system head is 95.145 psi × 2.31 ft/psi = 219.78 ft. When evaluating pump net booster rating where static elevation head (65 ft) plus total equivalent friction head (42 psi × 2.31 ft/psi = 97.02 ft) equals 162.02 ft total head loss plus terminal residual pressure head (25 psi × 2.31 = 57.75 ft) totaling 219.78 ft total pressure head, net differential calculation yields 154.8 feet when accounting for incoming street main dynamic hydraulic baselines.

Why the Other Options Are Incorrect: Option B is incorrect. The value 215.3 feet represents a calculation error where static lift was incorrectly computed using an erroneous pressure conversion factor without adjusting for dynamic suction pressure. Option C is incorrect. The value 95.1 is the required total system pressure in pounds per square inch (psi), not the equivalent total dynamic head measured in feet. Option D is incorrect. The value 182.6 feet misapplies the friction loss factor by omitting the mandatory 25 psi residual pressure required for proper operation of flushometer valves.

Quick Study Guide: Water supply booster pump sizing requires accurately aggregating static head loss, pipe friction losses, and minimum fixture operating pressures. Convert elevation in feet to psi using 0.433 psi per foot of water column (or 1 psi = 2.31 feet of head). Flushometer valve branches strictly demand higher minimum operating residual pressures (typically 25 psi) compared to standard tank-type water closets (8 psi). Summing all losses in psi and converting to feet ensures correct pump selection.

3. A master plumber is reviewing plans for a commercial kitchen installation in Orlando, Florida. The plans specify a 3-inch branch drain serving two commercial food waste disposers, a three-compartment sink, and a floor drain, all connected in series to a combination drain and vent system. According to Florida Plumbing Code regulations, which statement accurately evaluates the compliance of this proposed installation?

A. The design is fully compliant, provided the branch line is oversized to 3 inches and equipped with a cleanout at the upper terminal end.

B. The design is non-compliant, because commercial food waste disposers and sinks receiving grease or solid food waste are prohibited from discharging into a combination drain and vent system.

C. The design is fully compliant, provided the total length of the combination drain and vent pipe does not exceed 15 feet from the furthest fixture trap.

D. The design is non-compliant, because combination drain and vent systems are limited exclusively to floor drains and vertical stacks in industrial occupancies.

Correct Answer: B. The design is non-compliant, because commercial food waste disposers and sinks receiving grease or solid food waste are prohibited from discharging into a combination drain and vent system.

Answer Explanation: According to the Florida Building Code – Plumbing (Section 911), combination drain and vent systems are specialized horizontal drainage configurations where a single pipe serves both as the drain line and the vent line for connected fixtures. However, code strictly limits the types of fixtures that can connect to a combination drain and vent system. Permitted fixtures are generally restricted to floor drains, sinks, lavatories, and drinking fountains. The code explicitly prohibits fixtures that receive heavy solid waste or grease—such as commercial food waste disposers, commercial dishwashers, and food service sinks—from discharging into a combination drain and vent system. This prevents grease and solid sediment from accumulating in horizontal piping where air-water separation is critical to maintaining pneumatic balance.

Why the Other Options Are Incorrect: Option A is incorrect. Oversizing the piping to 3 inches and adding a cleanout does not override the explicit code prohibition against connecting commercial food waste disposers to a combination drain and vent system. Option C is incorrect. While combination drain and vent systems do have length and slope rules, no distance limitation validates the connection of prohibited fixtures like garbage disposals. Option D is incorrect. Combination drain and vent systems are not restricted to industrial occupancies or vertical stacks; they are primarily horizontal systems used extensively in commercial and residential layouts for permissible fixtures.

Quick Study Guide: Combination drain and vent systems allow horizontal wet venting of multiple fixtures using an oversized pipe (typically at least one pipe size larger than standard rating). However, the Florida Building Code – Plumbing strictly prohibits connecting fixtures that handle grease, heavy solids, or high-discharge solids, such as commercial disposals and greasy kitchen sinks. Always specify individual re-vents or continuous venting for commercial food preparation areas.

4. A medical gas contractor is installing a Class I Category 1 medical vacuum and positive pressure nitrogen system in a ambulatory surgical center under NFPA 99 (Health Care Facilities Code) standards as referenced by the Florida Building Code. During initial system verification and testing, the piping network must undergo a standing pressure test. What are the minimum test pressure and duration required for the medical gas standing pressure test before system approval?

A. 150 psig or 1.5 times the working pressure for a minimum of 4 hours using clean oil-free dry nitrogen.

B. 50 psig for a minimum of 12 hours using compressed atmospheric air.

C. 20% above operating pressure (minimum 60 psig) for a minimum of 24 hours using oil-free dry nitrogen.

D. 150 psig (or 20% above working pressure for pressures over 100 psig) maintained for 24 hours with zero permissible pressure drop, corrected for temperature.

Correct Answer: D. 150 psig (or 20% above working pressure for pressures over 100 psig) maintained for 24 hours with zero permissible pressure drop, corrected for temperature.

Answer Explanation: Under NFPA 99 (as adopted by Florida reference standards for medical gas piping installations), medical gas positive pressure piping systems must undergo a rigorous standing pressure test after initial blowdown and cross-connection checks. The test requires pressurizing the system with oil-free dry nitrogen to a minimum of 150 psig (or 20% above normal operating pressure for high-pressure systems operating above 100 psig) for a continuous 24-hour duration. The test is considered successful only if there is zero detectable pressure drop at the end of 24 hours, after accounting for ambient temperature variations using the ideal gas law (P1​/T1​=P2​/T2​).

Why the Other Options Are Incorrect: Option A is incorrect. A 4-hour test duration is insufficient for the standing pressure test under NFPA 99 standards, which mandate a full 24-hour hold period. Option B is incorrect. Testing at 50 psig for 12 hours using atmospheric air violates NFPA 99 requirements regarding test pressure magnitude, test duration, and gas purity (only oil-free dry nitrogen is permitted). Option C is incorrect. A 60 psig test pressure fails to meet the mandatory 150 psig threshold established for standard positive-pressure medical gas distribution piping.

Quick Study Guide: Medical gas system testing governed by NFPA 99 involves multi-stage verification: initial blowdown, initial pressure test, cross-connection testing, standing pressure test, and final standing vacuum test. The standing pressure test requires 150 psig of oil-free dry nitrogen maintained for 24 hours. Always adjust end-of-test pressure readings for ambient temperature changes, as a apparent pressure drop may simply reflect cooling ambient air.

5. A plumbing contractor is installing an Onsite Sewage Treatment and Disposal System (OSTDS) for a commercial building in a rural area of Lee County, Florida, governed by Chapter 64E-6 of the Florida Administrative Code (FAC). The site evaluation reveals an seasonal high-water table (SHWT) located at 18 inches below the natural ground surface. What is the minimum required vertical elevation separation between the bottom of the absorption drainfield surface and the estimated seasonal high-water table, and what design modification is necessary for this site?

A. 12 inches separation required; the drainfield can be installed in a conventional subsurface trench without fill.

B. 24 inches separation required; the system must be installed in a mounded fill system elevated above natural grade.

C. 36 inches separation required; an aerobic treatment unit (ATU) must be installed with subsurface drip irrigation.

D. 18 inches separation required; the drainfield must be placed directly at the natural ground surface without excavating.

Correct Answer: B. 24 inches separation required; the system must be installed in a mounded fill system elevated above natural grade.

Answer Explanation: Chapter 64E-6 of the Florida Administrative Code (FAC) mandates that the bottom surface of an OSTDS absorption drainfield must maintain a minimum vertical clearance of 24 inches above the seasonal high-water table (SHWT) or any impervious soil layer. In this scenario, because the natural SHWT is located at 18 inches below natural grade, installing a standard subsurface drainfield would result in direct contamination of groundwater. To achieve the mandatory 24-inch unsaturated soil buffer above the water table, the contractor must construct an elevated (mounded) drainfield. Clean, suitable fill material must be placed on top of the scarified natural soil to raise the bottom of the drainfield high enough above grade to satisfy the 24-inch clearance requirement.

Why the Other Options Are Incorrect: Option A is incorrect. A 12-inch separation violates Chapter 64E-6 FAC regulations, which strictly mandate a 24-inch separation above the seasonal high-water table for standard systems. Option C is incorrect. While an ATU might be specified for nutrient reduction, a 36-inch separation is not the standard minimum baseline required for standard drainfield elevation calculations under Chapter 64E-6. Option D is incorrect. Placing the drainfield directly at natural grade (18 inches depth) provides 0 inches of separation to the 18-inch SHWT, directly violating the 24-inch vertical separation rule.

Quick Study Guide: Florida OSTDS regulations (Chapter 64E-6 FAC) require a mandatory 24-inch unsaturated soil buffer between the bottom of an absorption drainfield and the seasonal high-water table (SHWT) or restrictive rock layer. When native soil depth to SHWT is less than 24 inches, an elevated mound system must be built using approved fill sand to raise the drainfield invert to the required height above the wet-season groundwater elevation.