Mississippi Mechanical Contractor Examination

Per the International Mechanical Code, what protective control is required on steam and hot-water boilers to shut off the fuel supply if the water level falls below a safe point?

• AA high-limit aquastat only
• BA low-water cutoff
• CA flow switch on the expansion tank
• DA manual reset pressuretrol only

A closed-loop hydronic heating circuit delivers 80,000 Btu/h with a design water temperature drop of 20°F. Using GPM = Btu/h ÷ (500 × ΔT), what is the required flow?

• A4 gpm
• B6 gpm
• C8 gpm
• D16 gpm

In a closed hydronic heating system, where should the circulator be arranged relative to the expansion tank for stable fill pressure?

• APump toward the expansion tank so the tank absorbs pump head
• BPump away from the expansion tank, which is the point of no pressure change
• CInstall the expansion tank on the suction of a booster only, never on the boiler loop
• DOmit the expansion tank if the relief valve is set at 30 psi

What is the typical pressure-relief-valve setting on a residential ASME hot-water heating boiler?

• A15 psi
• B30 psi
• C50 psi
• D150 psi

Where is an air separator most effective on a hot-water boiler loop?

• AOn the coldest return, just before the circulator suction
• BOn the boiler supply outlet, where the water is hottest and air is least soluble
• COn the compression tank drain only
• DOn a dead-end high point with no flow through the separator

Makeup water that automatically feeds a closed hydronic heating boiler must be protected against which hazard?

• ABackflow of chemically treated boiler water into the potable supply
• BExcessive condensate acidity in the vent
• COil logging of the compression tank
• DShort-cycling of the low-water cutoff only

Per the International Fuel Gas Code, an individual appliance shutoff valve shall be located in the same room as the appliance and not more than how far from the appliance?

• A3 feet
• B6 feet
• C12 feet
• D25 feet

Where a gas appliance does not have a factory sediment trap, how shall the field sediment trap be built and located per the IFGC?

• AA tee with a capped nipple in the bottom opening, installed downstream of the appliance s…
• BA 90-degree elbow drip at the meter only
• CA union installed upstream of the shutoff valve
• DA plugged tee in the vent connector

When pressure-testing a new low-pressure fuel-gas piping system under the IFGC, what is the minimum test pressure?

• AThe appliance working pressure of about 7 inches water column
• B1.5 times the proposed maximum working pressure, but not less than 3 psig
• C10 psig for every system, regardless of volume
• D50 psig, the same as a potable-water test

Using the IFGC longest-length method and this excerpt of Table 402.4(2) (Schedule 40 metallic pipe, natural gas, inlet less than 2 psi, 0.5 inch w.c. drop) at 40 feet — 1/2 inch = 81 cfh, 3/4 inch = 170 cfh, 1 inch = 320 cfh — what is the smallest pipe that can supply a 100,000 Btu/h furnace (100 cfh at 1,000 Btu/cu ft) that is 40 feet of developed length from the meter?

• A3/8 inch
• B1/2 inch
• C3/4 inch
• D1 inch

Which test medium is prohibited for pressure-testing fuel-gas piping?

• AAir
• BNitrogen
• CCarbon dioxide
• DOxygen

Corrugated stainless steel tubing (CSST) gas piping shall be bonded to the electrical service grounding electrode system with a copper bonding jumper not smaller than which size?

• A12 AWG
• B10 AWG
• C8 AWG
• D6 AWG

What is the IFGC minimum burial depth for underground fuel-gas piping, and what additional requirement applies to underground nonmetallic gas pipe?

• A6 inches of cover, and a 14 AWG tracer wire
• B12 inches of cover, and an insulated tracer wire not smaller than 18 AWG for nonmetallic…
• C18 inches of cover, and no tracer if the pipe is yellow
• D24 inches of cover, and a bare steel tracer rod only

Why must a leaking LP-gas system be treated differently from a leaking natural-gas system when searching a building?

• ALP-gas is lighter than air and collects at the ceiling, while natural gas sinks
• BBoth gases have the same density as air, so only a combustible-gas indicator at mid-heigh…
• CUndiluted LP-gas is heavier than air and collects in low spaces, while natural gas is lig…
• DLP-gas cannot be detected with a combustible-gas indicator

What is the usual purpose of two-stage regulation on an LP-gas vapor system serving building appliances?

• ATo raise container pressure so appliances can use 10 psig burners
• BTo drop tank pressure in two steps so delivery pressure stays stable as tank pressure and…
• CTo mix air with propane before the building service
• DTo replace the appliance shutoff valve

Using the IFGC standard method, indoor combustion air requires 50 cubic feet of space volume per 1,000 Btu/h of appliance input. A 100,000 Btu/h furnace is installed in a closed 20 ft by 24 ft by 8 ft mechanical room with no outdoor-air openings. What is the correct conclusion?

• AThe room volume is 3,840 cu ft, which exceeds the 2,000 cu ft required, so indoor air is…
• BThe room volume is 3,840 cu ft, but 5,000 cu ft is required, so additional combustion air…
• CThe room volume is 5,000 cu ft, which exactly matches the requirement
• DThe standard method is not used for furnaces, only for water heaters

Per the International Plumbing Code, horizontal drainage piping inside a building shall have cleanouts at intervals not exceeding which distance?

• A50 feet
• B75 feet
• C100 feet
• D200 feet

Under the IPC, a cleanout serving a 6-inch building drain must be at least which size?

• A2 inches
• B3 inches
• C4 inches
• D6 inches

A horizontal building drain changes direction with a single 90-degree sweep. In addition to interval cleanouts, what does the IPC require at that change of direction?

• ANo extra cleanout, because a 90-degree sweep is self-scouring
• BA cleanout, because a cleanout is required at each change of direction greater than 45 de…
• CA manhole, because every 90-degree bend must be a manhole
• DTwo cleanouts, one on each side of every fitting regardless of angle

Per IPC Table 709.1, what drainage fixture-unit (DFU) value is assigned to a private 1.6 gpf water closet?

• A2 DFU
• B3 DFU
• C4 DFU
• D6 DFU

What is the IPC minimum clearance from the centerline of a water closet to a side wall or partition?

• A12 inches
• B15 inches
• C18 inches
• D21 inches

An automatic clothes-washer standpipe shall extend what distance above the weir of its trap?

• ANot less than 12 inches and not greater than 24 inches
• BNot less than 18 inches and not greater than 42 inches
• CNot less than 24 inches and not greater than 60 inches
• DAny height, provided the trap is 4 inches

A private bathroom group as defined in IPC Section 202 includes one 1.6 gpf water closet, one lavatory, and one bathtub. Using Table 709.1, what DFU value is used to size the drainage piping for that group?

• A3 DFU
• B5 DFU
• C6 DFU
• D8 DFU

What is the IPC minimum interior dimension of a shower compartment?

• A24 inches
• B30 inches
• C36 inches
• D42 inches

Every storage-tank water heater shall be equipped with which safety device?

• AA vacuum breaker only
• BA combination temperature-and-pressure relief valve, or separate temperature and pressure…
• CA boiler low-water cutoff piped to the flue
• DA 30 psi hydronic relief valve

Which installation of a water-heater T&P relief-valve discharge pipe complies with IPC 504.6?

• AReduced to 1/2 inch, run to a floor drain, and fitted with a shutoff valve for service
• BFull size of the valve outlet, not trapped, no end threads, no valves or tees, dischargin…
• CHard-piped directly into the sanitary tee of a laundry tray
• DRouted to the outdoors and capped to keep insects out

Which valve is a quarter-turn isolation valve with a full-open port that is preferred for shutoff duty but is a poor throttling valve?

• AGlobe valve
• BNeedle valve
• CBall valve
• DAngle globe valve

What is the primary purpose of a check valve in hydronic or water piping?

• ATo regulate flow to a design gpm
• BTo prevent reverse flow
• CTo reduce static pressure to 80 psi
• DTo vent air at a high point

Individual shower and tub-shower valves shall limit delivered water temperature to a maximum of which value?

• A105°F
• B110°F
• C120°F
• D140°F

A 45-degree rolling offset has an offset of 10 inches. Using the Pipefitters Handbook factor of 1.414, what is the travel (center-to-center length of the 45-degree pipe)?

• A10.0 inches
• B12.0 inches
• C14.1 inches
• D20.0 inches

A hydronic heating zone needs a valve that can be left partly open to set flow without destroying the disc. Which valve type is the correct choice?

• AStandard quarter-turn ball valve used as a throttle
• BGate valve cracked one turn off the seat
• CGlobe valve or a calibrated balancing valve
• DSwing check valve with the disc wired half open

Airflow in cubic feet per minute through a duct equals which product?

• AVelocity in fpm times duct length in feet
• BDuct face area in square feet times velocity in feet per minute
• CStatic pressure in inches w.g. times 4005
• DFriction rate times total equivalent length

In SMACNA HVAC Duct Construction Standards, Seal Class A requires sealing of which joints?

• ATransverse joints only
• BTransverse and longitudinal joints only
• CTransverse joints, longitudinal joints, and duct-wall penetrations
• DFlexible-duct collars only

A 12-inch by 8-inch rectangular supply duct is designed for 900 fpm. What is the airflow?

• A480 cfm
• B600 cfm
• C720 cfm
• D864 cfm

What are the IMC/SMACNA support limits for flexible air ducts?

• ASupport every 10 feet with sag not more than 2 inches per foot
• BSupport at intervals not exceeding 4 feet, with sag not more than 1/2 inch per foot
• CNo intermediate supports if the run is less than 25 feet
• DSupport only at the air handler and the register

From which of the following spaces does the IMC prohibit taking return air?

• AA conditioned living room
• BA hallway that serves bedrooms
• CA private garage
• DA finished basement family room that is part of the conditioned envelope

A supply duct passes through a fire-resistance-rated wall. What device is required in the duct at that penetration unless an exception applies?

• AA backdraft damper only
• BA listed fire damper installed in accordance with its listing
• CA volume damper set and locked at 50 percent
• DA flexible-duct connector in lieu of a damper

Per the IPC, a pressure-reducing valve is required when static water pressure exceeds which value?

• A60 psi
• B80 psi
• C100 psi
• D150 psi

IPC Table 604.3 lists the minimum flow pressure at a tank-type water closet as which value?

• A8 psi
• B15 psi
• C20 psi
• D35 psi

Per IPC Table 604.5, what is the minimum fixture-supply pipe size for a lavatory and for a kitchen sink?

• ALavatory 1/4 inch, kitchen sink 3/8 inch
• BLavatory 3/8 inch, kitchen sink 1/2 inch
• CLavatory 1/2 inch, kitchen sink 3/4 inch
• DBoth fixtures 3/4 inch

A second-floor battery of fixtures is 40 feet above the water-service entrance. Ignoring friction, what is the static pressure loss due to elevation? Use 0.433 psi per foot of water.

• A9.2 psi
• B13.3 psi
• C17.3 psi
• D40.0 psi

Unless an approved exception is used, the IPC requires what minimum horizontal separation between a water-service pipe and a building sewer?

• A12 inches
• B2 feet
• C5 feet
• D10 feet

Per IPC Table 308.5, what is the maximum horizontal hanger spacing for PVC pipe?

• A2 feet 8 inches
• B4 feet
• C6 feet
• D10 feet

What is the IPC maximum horizontal hanger spacing for copper or copper-alloy tubing 1-1/4 inch and smaller?

• A4 feet
• B6 feet
• C10 feet
• D12 feet