CSLB Trade — Plumbing (C-36) — All Questions

What is the primary purpose of the wax ring used when setting a water closet?

• a.to anchor the bowl to the studs
• b.to reduce flush noise
• c.to form a watertight, gastight seal between the bowl and the flange✓
• d.to level the bowl on an uneven floor

The wax ring compresses between the water closet horn and the flange to create a seal that stops water leaks and sewer gas. It is not a structural or leveling component. Bolts and shims handle alignment; the wax handles the seal.

An accessible (ADA/CBC) water closet must have the top of the seat at what height above the finished floor?

• a.10 to 12 inches
• b.24 to 28 inches
• c.17 to 19 inches✓
• d.20 to 24 inches

For an accessible water closet, the top of the seat must be 17 to 19 inches above the finished floor. This range lets a person transfer from a wheelchair. Standard (non-accessible) toilets are typically lower.

An accessible lavatory must provide knee and toe clearance underneath. The minimum height of the knee clearance space at the front edge is typically:

• a.34 inches
• b.40 inches
• c.24 inches
• d.27 inches✓

An accessible lavatory generally requires about 27 inches of clear knee height at the front edge, with the rim mounted no higher than 34 inches. Exposed hot water and drain piping beneath must be insulated or otherwise protected. These clearances let a wheelchair user roll under the fixture.

Grab bars at an accessible water closet must be designed to resist a minimum applied load of:

• a.250 pounds✓
• b.150 pounds
• c.100 pounds
• d.500 pounds

Grab bars and their fasteners and wall backing must be able to withstand at least a 250-pound point load in any direction. This ensures the bar supports a person safely. Adequate blocking must be installed in the wall to carry the load.

The minimum number of plumbing fixtures required for a building is determined primarily by:

• a.the color of the fixtures
• b.the water heater capacity
• c.the building's occupancy classification and occupant load✓
• d.the length of the water service

The minimum required plumbing fixtures are set by the occupancy type and the number of occupants, typically from a code table. This determines required water closets, lavatories, and other fixtures for each sex. Undersizing fixture counts is a common plan-check rejection.2022 California Plumbing Code (CPC) §422.1

A shower or tub-shower valve in a residence must be an approved anti-scald type that limits hot water temperature to a maximum of:

• a.120°F✓
• b.180°F
• c.140°F
• d.160°F

Individual shower and tub-shower control valves must be pressure-balancing or thermostatic anti-scald types limited to a maximum of 120°F at the outlet. This protects users from sudden temperature spikes and burns. The valve limit stop is set during installation.

A pressure-balancing shower valve protects a bather primarily by:

• a.increasing flow to 3 gpm automatically
• b.shutting off water if the drain clogs
• c.maintaining outlet temperature when cold or hot supply pressure changes✓
• d.venting the shower drain

A pressure-balancing valve senses changes in hot or cold supply pressure, such as a flushed toilet stealing cold water, and adjusts to keep the outlet temperature stable. This prevents a sudden scald or cold shock. It is one approved anti-scald method along with thermostatic valves.

The minimum required air gap between a fixture's water supply outlet and the fixture's flood-level rim protects against:

• a.backflow of contaminated water into the potable supply✓
• b.scalding
• c.water hammer
• d.thermal expansion

An air gap is a vertical space between the supply outlet and the flood-level rim of a fixture that prevents contaminated water from being siphoned back into the potable system. It is the most reliable backflow protection. The minimum gap depends on the outlet size and nearby walls.2022 California Plumbing Code (CPC) §603.3.1

A lavatory or sink is required to have an overflow only when:

• a.it is made of stainless steel
• b.the fixture design includes one; where provided, it must connect on the fixture side of the trap✓
• c.it serves a commercial kitchen
• d.it is set on a pedestal

Not every fixture must have an overflow, but where a fixture is furnished with one, the overflow passage must connect to the fixture side of the trap so its water is renewed and sealed. An overflow that connects on the sewer side would bypass the trap seal. The overflow must be designed so it cannot cause cross-contamination.

Plumbing fixtures must be constructed of materials that are:

• a.always cast iron
• b.rough-textured for grip
• c.porous to allow drying
• d.smooth, impervious, and free of concealed fouling surfaces✓

Fixtures must have smooth, impervious, nonabsorbent surfaces without concealed fouling areas so they stay sanitary and cleanable. Porous or rough surfaces would harbor bacteria and stains. This applies to the fixture body and its exposed surfaces.2022 California Plumbing Code (CPC) §402.1

A wall-hung urinal in a standard adult commercial restroom is typically set with the lip of the fixture at a maximum height above the floor of about:

• a.24 inches✓
• b.36 inches
• c.40 inches
• d.30 inches

For standard (non-child) use, a wall-hung urinal lip is commonly set no higher than about 24 inches above the finished floor. Accessible urinals must have the rim no higher than 17 inches. Manufacturer rough-in dimensions and accessibility rules govern the exact setting height.

Compared with a two-piece water closet, a one-piece (integral tank and bowl) water closet generally offers which advantage?

• a.no need for a wax ring
• b.elimination of the trap
• c.a larger flush volume
• d.fewer joints and a lower profile with easier cleaning✓

A one-piece water closet integrates the tank and bowl, so there are fewer joints to leak and a lower, smoother profile that is easier to clean. It still requires a wax ring seal to the flange and a trap. The choice is largely about maintenance and appearance.

A residential dishwasher discharge must be protected against backflow. Which method is an approved way to do this?

• a.run the hose in a straight downhill line
• b.connect the drain hose to the floor
• c.an approved dishwasher air gap fitting, or a high loop where permitted✓
• d.install a check valve only

A dishwasher drain must have an air gap to prevent waste water from siphoning back into the machine. An approved air-gap fitting mounted at the counter is the standard method; a high loop is accepted in some jurisdictions. A simple check valve alone is not adequate backflow protection.2022 California Plumbing Code (CPC) §807.3

A water heater's T&P relief valve must be installed so that it is:

• a.located below the tank base
• b.concealed inside the wall
• c.sealed permanently to prevent tampering
• d.accessible for inspection, testing, and replacement✓

The relief valve must remain accessible so it can be inspected, manually tested, and replaced when needed. Concealing or sealing it would prevent required maintenance. Its sensing element must reach into the top of the tank where water is hottest.2022 California Plumbing Code (CPC) §608.3

Which of the following is prohibited between a water heater and its T&P relief valve?

• a.a temperature sensor well
• b.the tank tapping itself
• c.any shutoff or check valve✓
• d.a listed dielectric fitting

No shutoff, check valve, or other valve may be installed between the tank and the T&P relief valve, because it could isolate the valve and defeat over-pressure protection. The relief valve must sense tank conditions directly. Only approved fittings that do not restrict operation are allowed.2022 California Plumbing Code (CPC) §608.3

A water heater must be installed so that:

• a.the burner faces a combustible wall
• b.it is fully enclosed with no access
• c.the controls are hidden behind drywall
• d.it is accessible for inspection, service, and replacement✓

Water heaters must be located and installed with adequate access and clearances for inspection, servicing, and replacement. Enclosing the appliance without access violates the code and manufacturer listing. Required working space keeps the unit serviceable and safe.2022 California Plumbing Code (CPC) §507.0

The temperature-sensing element of a water heater T&P relief valve must be located so that it senses:

• a.the incoming cold water
• b.the water in the top 6 inches of the tank✓
• c.the flue gas temperature
• d.the room air temperature

The T&P valve's temperature element must extend into the top 6 inches of the tank, where the water is hottest, so it responds to dangerous overheating. Sensing cooler water lower in the tank would delay relief. Correct placement is essential to the valve's protective function.2022 California Plumbing Code (CPC) §608.3

A thermal expansion tank installed on a water heater system must be:

• a.supported so its weight is not carried by the connecting piping✓
• b.installed only on the hot outlet
• c.left unpressurized
• d.filled completely with water

An expansion tank, especially when full of water, is heavy and must be independently supported so its weight does not stress or break the piping. The air side is precharged to match system pressure. Proper support and precharge let the tank absorb thermal expansion reliably.

Water hammer arrestors are installed on a water distribution system primarily to:

• a.absorb the shock of quick-closing valves and reduce pipe noise and damage✓
• b.raise system pressure
• c.prevent backflow
• d.filter sediment

Quick-closing valves, such as those on clothes washers and dishwashers, cause a pressure surge (water hammer) that bangs pipes and can loosen joints. Water hammer arrestors provide a cushion of air or a piston to absorb that shock. They are installed near the quick-closing valve they protect.2022 California Plumbing Code (CPC) §609.10

An outdoor hose bibb (sillcock) must be protected against backflow by:

• a.a check valve on the water heater
• b.a pressure-reducing valve
• c.an expansion tank
• d.an atmospheric or listed hose-connection vacuum breaker✓

A hose bibb can create a cross-connection when a hose is submerged in contaminated water, so it must have a hose-connection vacuum breaker (or be a listed anti-siphon type). This device admits air to break any back-siphonage. It protects the potable supply from garden or utility contaminants.2022 California Plumbing Code (CPC) §603.5.7

Each fixture supply to a lavatory or water closet is commonly fitted with an angle stop primarily to:

• a.arrest water hammer
• b.allow the fixture to be shut off individually for service✓
• c.reduce the flow rate
• d.prevent backflow

An angle stop (fixture shutoff valve) lets a single fixture be isolated for repair or replacement without shutting off water to the whole building. It is installed on the supply riser to the fixture. This is a convenience and service requirement, not a backflow or flow-control device.

A water heater installed in an attic must be reached by a passageway and working platform. A typical minimum requirement is a solid, continuous passageway not less than:

• a.6 inches wide
• b.12 inches wide
• c.48 inches wide with stairs
• d.30 inches wide with a level working platform at the appliance✓

Attic-installed water heaters generally require a solid passageway at least 30 inches wide from the access opening to the appliance, plus a level working platform in front of the service side. A light and receptacle are also commonly required. These provisions let the unit be serviced safely.

Cross-connection control in a potable water system is intended to:

• a.increase water pressure at fixtures
• b.reduce pipe corrosion
• c.prevent nonpotable or contaminated water from entering the potable supply✓
• d.silence water hammer

Cross-connection control uses air gaps and backflow prevention devices to keep contaminated or nonpotable water from flowing back into the drinking water system. Backflow can occur by back-siphonage or back-pressure. Protecting every actual or potential cross-connection is a core plumbing safety requirement.2022 California Plumbing Code (CPC) §603.2

A floor drain located in a room that is used infrequently may lose its trap seal by evaporation. The approved way to keep the seal is to provide:

• a.a trap primer or an approved trap seal protection device✓
• b.a larger trap arm
• c.a second floor drain nearby
• d.a deeper cleanout

In little-used areas, water in a floor drain trap can evaporate and let sewer gas enter. A trap primer periodically adds water to maintain the seal, or an approved barrier-type trap seal device may be used. This keeps the required 2-to-4-inch seal intact.

A plumber replaces a water heater in a finished basement over a slab where a leak would not damage anything below, but the local code still requires spill protection. If a drain pan is installed, its drain must:

• a.be capped until a leak occurs
• b.connect directly into the sanitary sewer without an air gap
• c.discharge by gravity to an approved location where it will be readily observed✓
• d.loop upward before discharging

When a drain pan is installed, its drain line must run by gravity to an approved discharge point where a leak becomes readily visible, so the problem is noticed early. It must not tie directly into the sanitary drainage system without proper separation. Visibility of the discharge is the key requirement.2022 California Plumbing Code (CPC) §507.5

A natural gas furnace is rated at 100,000 BTU/hr input. Using a heating value of 1,000 BTU per cubic foot, what gas demand in cubic feet per hour (cfh) must the piping supply?

• a.10 cfh
• b.10,000 cfh
• c.1,000 cfh
• d.100 cfh✓

Divide the BTU/hr input by the heating value: 100,000 divided by 1,000 equals 100 cubic feet per hour. This cfh demand is the number you carry into the gas pipe sizing tables. Natural gas is commonly figured at about 1,000 BTU per cubic foot.California Plumbing Code, Fuel Gas provisions

Where must an accessible manual shutoff valve be located relative to a gas appliance it serves?

• a.Concealed inside the appliance cabinet
• b.Within 6 feet of the appliance, in the same room✓
• c.At least 20 feet away for safety
• d.Only at the gas meter, no valve needed at the appliance

Each appliance requires an accessible manual shutoff valve located in the same room, generally within 6 feet of the appliance. This lets a technician isolate that unit for service without shutting off the whole building. The valve must remain accessible, not buried behind the appliance.California Plumbing Code, Fuel Gas provisions

What is the primary purpose of a sediment trap (drip leg) installed ahead of a gas appliance control?

• a.To increase gas pressure at the burner
• b.To vent excess gas to the outdoors
• c.To act as a required shutoff valve
• d.To catch moisture and debris before they reach the appliance gas valve✓

A sediment trap is a short capped nipple that catches condensate, scale, and dirt carried in the gas stream so they drop out instead of fouling the appliance gas control. It is installed downstream of the appliance shutoff valve and as close as practical to the appliance inlet. It does not regulate pressure or replace the shutoff valve.California Plumbing Code, Fuel Gas provisions

A helper wants to route a flexible appliance connector through the back wall of a cabinet to reach the gas cooktop. What is the correct rule?

• a.Not allowed; connectors must not pass through walls, floors, partitions, or ceilings✓
• b.Allowed if the connector is at least 6 feet long
• c.Allowed if the connector is copper
• d.Allowed if wrapped with tape where it passes through

Listed appliance connectors are for the final connection only and must not pass through any wall, floor, partition, ceiling, or appliance housing. Running one through a wall can chafe or crimp the thin tubing and hide a leak. If piping must penetrate the wall, use rigid pipe to a shutoff valve on the appliance side, then the connector.

For a rough-in pressure test of a new low-pressure gas piping system, which test condition is commonly required by the plumbing code?

• a.Air or inert gas at not less than 10 psi held for at least 15 minutes✓
• b.Oxygen at 50 psi for 10 minutes
• c.Water at 5 psi for 5 minutes
• d.Natural gas at working pressure for 1 hour

New gas piping is proof-tested with air or an inert gas, typically at not less than 10 psi held for a minimum of 15 minutes with no drop on the gauge (verify the value required by your local jurisdiction). The medium is never oxygen or fuel gas, and never water, because gas lines must stay dry. A pressure loss during the hold indicates a leak to locate and repair.California Plumbing Code, Fuel Gas provisions

A propane (LP) appliance has an input of 75,000 BTU/hr. Using an approximate heating value of 2,500 BTU per cubic foot for propane, what is its demand in cfh?

• a.3 cfh
• b.30 cfh✓
• c.300 cfh
• d.75 cfh

For propane, divide the input by about 2,500 BTU per cubic foot: 75,000 divided by 2,500 equals 30 cubic feet per hour. Propane carries far more energy per cubic foot than natural gas, so its cfh demand is much smaller for the same BTU load. Always match the sizing table to the correct fuel.California Plumbing Code, Fuel Gas provisions

Corrugated stainless steel tubing (CSST) gas systems have an important electrical requirement. What is it?

• a.It must be electrically bonded, commonly with a jumper of at least No. 6 AWG copper✓
• b.It must be filled with inert gas
• c.It must be painted red
• d.It must be pressurized to 25 psi

CSST is thin-wall tubing that can be damaged by an electrical arc from a nearby lightning strike, so the manufacturer and code require it to be bonded to the electrical grounding system. Bonding is commonly done with a clamp on the rigid pipe or CSST fitting and a jumper of at least No. 6 AWG copper. Always follow the CSST manufacturer's listed bonding instructions.

Under what condition is copper tubing generally permitted for a natural gas distribution system?

• a.Copper is never allowed for any fuel gas
• b.Only where the gas supply is not corrosive to copper, i.e., low hydrogen sulfide content✓
• c.Copper is always allowed with no conditions
• d.Copper is allowed for propane but never natural gas

Copper may be used for fuel gas only where the delivered gas will not corrode it, which means a low hydrogen sulfide (sulfur) content below the code threshold. Many utilities do not guarantee this, so black steel is the default choice. Where copper is used it must be listed for gas and properly identified, and interior surfaces must not shed material that could plug controls.

When using the longest-length (longest-run) method to size a gas piping system, which length is used to select pipe size for every section?

• a.The shortest branch length
• b.Exactly 100 feet regardless of the layout
• c.The length of the smallest appliance connector
• d.The total developed length from the meter to the most remote outlet✓

In the longest-length method you find the total developed length from the gas source to the farthest outlet, then use that single length column in the table to size every section based on its own cfh demand. Using the most remote run assures adequate pressure everywhere in the system. Add equivalent lengths for fittings where the code or table requires it.

What is the typical manifold (burner) pressure delivered to a standard residential natural gas appliance?

• a.About 3.5 inches water column✓
• b.About 14 inches water column
• c.About 11 inches water column
• d.About 2 psi

A standard natural gas appliance operates at a manifold pressure of about 3.5 inches water column, set by the appliance regulator. Propane appliances by contrast typically run near 10 to 11 inches water column. Manometer readings in inches of water column are how these low pressures are measured and verified.

A single gas main serves a 40,000 BTU/hr water heater, a 100,000 BTU/hr furnace, and a 65,000 BTU/hr range. What total connected load must the main be sized to carry?

• a.165,000 BTU/hr
• b.40,000 BTU/hr
• c.205,000 BTU/hr✓
• d.100,000 BTU/hr

The section feeding all three appliances must carry the sum of their inputs: 40,000 plus 100,000 plus 65,000 equals 205,000 BTU/hr. Convert to cfh (about 205 cfh for natural gas) and size that section for the full connected load. Individual branches downstream only carry the demand beyond that point.

What is the function of a gas pressure regulator in a piping system?

• a.To trap sediment before the appliance
• b.To reduce and hold gas pressure to a stable, lower value for downstream piping or an appliance✓
• c.To bond the piping electrically
• d.To measure total gas consumption

A regulator takes a higher, sometimes variable, supply pressure and delivers a lower, steady outlet pressure that the piping and appliance are designed for. Service and line regulators are used where supply pressure exceeds what the appliances need, such as stepping a 2 psi system down at each appliance. Regulators are not meters, sediment traps, or bonding devices.

A sediment trap is generally NOT required at which of the following appliances?

• a.A gas water heater
• b.A listed range, clothes dryer, or outdoor grill, where exempted by code✓
• c.A gas boiler
• d.A gas furnace

Code generally exempts certain appliances such as listed ranges, clothes dryers, and outdoor grills from the sediment-trap requirement, while furnaces, boilers, and water heaters still require one. The trap protects the automatic gas valve on heating appliances from moisture and debris. Always check the specific list in the adopted code and the appliance instructions.California Plumbing Code, Fuel Gas provisions

Which material is the traditional default choice for interior fuel gas piping in residential and light commercial work?

• a.Black (steel) pipe with malleable iron or steel fittings✓
• b.Cast iron soil pipe
• c.Type M copper for all gases
• d.PVC plastic pipe

Black steel pipe with threaded malleable-iron or steel fittings is the traditional workhorse for interior gas distribution. PVC and other thermoplastics are used only underground where listed for gas, not for interior aboveground piping. Cast iron soil pipe is a drainage material and is not approved for fuel gas.

A tankless natural gas water heater lists an input of 199,000 BTU/hr. Using 1,000 BTU per cubic foot, what gas demand must the branch supplying it be sized for?

• a.99 cfh
• b.19.9 cfh
• c.199 cfh✓
• d.1,990 cfh

Divide input by heating value: 199,000 divided by 1,000 equals 199 cubic feet per hour. High-input tankless heaters often need a larger branch and meter than a tank-type unit because of this large instantaneous demand. Verify the meter and upstream piping can also supply this cfh at the required pressure.

A building is served by an elevated-pressure (2 psi) gas system. What component is required near each appliance?

• a.Nothing extra; appliances run fine on 2 psi
• b.A sediment trap that also reduces pressure
• c.A second gas meter at every appliance
• d.A line pressure regulator to step the 2 psi down to the appliance operating pressure✓

In a 2 psi (elevated-pressure) system, the smaller high-pressure piping must be stepped down by a line pressure regulator to the low pressure (inches of water column) each appliance needs. Without the regulator the appliance regulator would be overwhelmed and the burner would over-fire. The regulator is a separate device from the shutoff valve and sediment trap.

What is the typical operating (manifold) pressure for a standard residential propane (LP) appliance?

• a.About 10 to 11 inches water column✓
• b.About 2 psi
• c.About 3.5 inches water column
• d.About 25 inches water column

Standard propane appliances operate at roughly 10 to 11 inches water column at the manifold, higher than natural gas at about 3.5 inches. This is why an appliance and its regulator must be matched to the correct fuel; installing a natural gas orifice on propane, or the reverse, is dangerous. Confirm the appliance rating plate and regulator spring for the fuel supplied.

Which statement about listed flexible appliance connectors is correct?

• a.They must not pass through a wall, floor, ceiling, or partition and must be accessible✓
• b.They may be concealed permanently inside a finished wall
• c.They are the same thing as CSST distribution tubing
• d.They may be spliced together to gain length

A listed appliance connector is a single, one-piece final connection that must remain accessible and must not be run through walls, floors, ceilings, or partitions. Connectors may not be joined end-to-end or spliced to reach farther. CSST is a distribution piping product with its own rules and is not the same as a short appliance connector.

A sizing table (0.5 psi drop, natural gas) shows that 3/4-inch schedule 40 pipe at a 40-foot run carries 170 cfh, and 1-inch pipe carries 320 cfh. A section must supply a 250,000 BTU/hr load over that 40-foot run. What is the smallest listed size that works?

• a.1-inch pipe✓
• b.1/2-inch pipe
• c.No pipe in the table is large enough
• d.3/4-inch pipe

Convert the load: 250,000 divided by 1,000 equals 250 cfh. The 3/4-inch pipe carries only 170 cfh, which is not enough, but the 1-inch pipe carries 320 cfh, which exceeds 250. Therefore 1-inch is the smallest listed size that meets the demand at that length.

Where should the sediment trap be installed in relation to the appliance shutoff valve and the appliance gas control?

• a.Anywhere on the branch is fine
• b.Only inside the appliance cabinet
• c.Upstream of the shutoff valve, near the meter
• d.Downstream of the shutoff valve and as close as practical to the appliance inlet, ahead of the gas control✓

The sediment trap is placed downstream of the appliance shutoff valve and just ahead of the appliance gas control, as close as practical to the appliance inlet. In that position it can catch debris before the gas reaches the control valve. It is typically a tee with a short capped nipple pointing down.California Plumbing Code, Fuel Gas provisions

What is a common standard delivery pressure of natural gas to a typical single-family residence downstream of the utility meter?

• a.About 15 psi
• b.About 60 psi
• c.About 1/4 psi, roughly 7 inches water column✓
• d.About 100 inches water column

A common residential natural gas service delivers roughly 1/4 psi, which is about 7 inches water column, at the outlet of the meter and pressure regulator. The appliance regulator then trims this to about 3.5 inches water column at the burner. Elevated-pressure (2 psi) systems exist but require a line regulator at each appliance.

Low gas pressures for appliances are commonly expressed in inches of water column. Which instrument directly reads this pressure during setup and testing?

• a.A megohmmeter
• b.A pyrometer
• c.A manometer (water column or digital)✓
• d.An amp clamp

A manometer, either a U-tube filled with water or a digital equivalent, directly measures the low gas pressures used by appliances in inches of water column. It is the standard tool for checking supply pressure and manifold pressure. A megohmmeter, amp clamp, and pyrometer measure electrical resistance, current, and temperature instead.

When performing a gas piping pressure test, why should the test gauge have an appropriate scale for the test pressure?

• a.Because gauges must always read in psi, never inches of water
• b.Because a bigger gauge always reads more accurately
• c.So that a small pressure drop is readable, the gauge increment should be fine enough to detect a leak✓
• d.Because the code bans digital gauges

The test gauge or manometer must have an increment fine enough that a small leak shows up as a readable pressure drop over the hold period. An oversized gauge with coarse graduations can hide a slow leak. Match the instrument range and resolution to the required test pressure and the sensitivity needed.

What best describes CSST used in gas distribution?

• a.Plastic pipe for underground gas only
• b.Rigid black steel pipe with threaded joints
• c.A rubber appliance connector
• d.Corrugated stainless steel tubing, a flexible listed distribution system installed per its manufacturer's instructions✓

CSST stands for corrugated stainless steel tubing, a flexible, semi-rigid distribution piping system with proprietary fittings that speeds installation compared to threaded steel. It must be installed strictly per its listing and manufacturer instructions, including protection from physical damage and required electrical bonding. It is not the same as a short appliance connector or plastic underground pipe.

Two runs leave the meter: Run A is 55 feet to the farthest outlet; Run B is 30 feet. Using the longest-length method, which length column governs sizing of the entire system?

• a.The 30-foot column
• b.The average, 42.5 feet
• c.The sum, 85 feet
• d.The 55-foot column✓

The longest-length method uses the single longest developed run from the source to the most remote outlet, here 55 feet, to select the length column for the whole system. Each section is then sized from that column by its own cfh demand. You do not average or add the runs together.