18.1 Pipe Sizing, Valves, Fittings, Sealants & Layout

18.1 Pipe Sizing, Valves, Fittings, Sealants & Layout

Trade Area A (Pre-Installation) is 14 percent of the Class A trade exam and 12 percent of Class B. After plans, energy, and duct design, the outline asks you to size pipe from tables, account for liquid flow and friction, select valves and fittings, apply pipe sealants, and lay out piping. The 2026 Air Conditioning CBT reference that exists for this cluster is Pipefitters Handbook, 3rd Edition (1967) (Forrest R. Lindsey), listed as R82, together with Florida Building Code — Mechanical, 2023. This is not a “we always run 3/4-inch to the air handler” item.

Quick Answer: Convert load to flow with GPM = Btu/h ÷ (500 × ΔT). Size the pipe from the handbook friction and velocity tables, add equivalent lengths of fittings and valves, and lay the circuit out with isolation, drains, vents, expansion, and listed thread sealant. Class B may install hydronic piping and insulation; Class B does not pick up boilers, unfired pressure vessels, or pneumatic control piping.

Why pipe size is a design number

Water (or glycol) is the heat-transport fluid on chilled-water, hot-water, and condenser-water systems. The machine’s capacity is in Btu per hour. The pipe’s job is to move that heat as mass flow × specific heat × temperature change. Undersize the pipe and friction head explodes, the pump leaves its curve, coils starve, and the main sings. Oversize it and you waste money, drop below the velocity that helps sweep air and dirt, and still fail the exam item if the schedule called a specific diameter.

Nominal pipe size (NPS) is not the inside diameter. A 1-inch Schedule 40 steel pipe has an outside diameter of 1.315 inches and an inside diameter of about 1.049 inches. Copper Type L, Type K, and Type M have different wall thicknesses at the same nominal size. Handbook friction tables are built on the actual ID of the schedule or type you are installing. Reading the Type M row when Division 23 specified Type L is a wrong head number.

F.S. 489.105(3)(f) (Class A) and (3)(g) (Class B) both include piping and insulation of pipes, vessels, and ducts. That is hydronic, refrigerant, condensate, and process piping that completes the HVAC system. It is not potable water, sanitary sewer, or swimming-pool piping, and it is not new interior LP or natural-gas fuel lines (the statutory exception is disconnecting or reconnecting changeouts of those appliances). Class A also lists pressure and process piping and pneumatic control piping; Class B’s definition does not.

The 500 constant — worked GPM examples

For water:

(\text{GPM} = \dfrac{\text{Btu/h}}{500 \times \Delta T})

The 500 is unit conversion, not a code fudge factor: 8.33 lb/gal × 60 min/h × 1 Btu/lb-°F ≈ 500. Glycol blends need a different constant because specific heat and density drop. Do not blindly use 500 on a 40 percent propylene-glycol loop.

Cooling. A chilled-water coil is scheduled for 120,000 Btu/h (10 tons) at a 10°F leaving-minus-entering ΔT:

(\text{GPM} = 120{,}000 \div (500 \times 10) = 24\ \text{gpm})

A planning shortcut is about 2.4 gpm per ton at 10°F ΔT — the same formula: (12{,}000 \div 5{,}000 = 2.4). At a 12°F ΔT the same 10 tons needs (120{,}000 \div 6{,}000 = 20) gpm. Stretching ΔT to “save pipe” only works if the coil, chiller, and control valve are actually rated at that flow.

Heating. A hydronic coil delivers 100,000 Btu/h with a 20°F drop:

(\text{GPM} = 100{,}000 \div (500 \times 20) = 10\ \text{gpm})

Halving ΔT doubles gpm. FBC Mechanical hydronic installations follow the listing and the approved drawings, not a field ΔT invented at the balancing valve after the pipe is already too small.

Friction, velocity, and equivalent length

The handbook (and manufacturer charts) plot flow versus friction head per 100 feet of pipe and velocity in feet per second. The exam method is:

1. Compute gpm from the load and ΔT.
2. Pick a trial pipe size.
3. Read friction (feet of water per 100 feet) and velocity (ft/s).
4. Measure the developed length of the circuit from the piping plan (architect’s 1/4-inch or 1/8-inch scale — Chapter 15).
5. Convert every elbow, tee, reducer, and valve to equivalent feet of straight pipe from the handbook fitting tables.
6. Total equivalent length ÷ 100 × friction per 100 feet = pipe-and-fitting head. Add coil, control-valve, strainer, and (on open systems) elevation to get pump head.

Worked friction add-up. Flow is 24 gpm. The handbook row you selected shows 4 feet of head per 100 feet. The run measures 80 feet of pipe. Two standard 90° elbows, a tee on the branch, a strainer, and two isolation valves add 120 equivalent feet from the fitting table. Total equivalent length = 200 feet. Pipe-and-fitting head = (200 / 100 \times 4 = 8) feet. If the coil is 12 feet and the two-way valve is 5 feet, the pump must make about 25 feet of head at 24 gpm. Selecting “24 feet because it matches gpm” is not a method.

Velocity is the trap next to friction. Closed-loop HVAC water is commonly kept in a moderate band — roughly 2 to 4 feet per second in small branches and often not more than about 8 feet per second in larger mains — so you do not erode fittings or transmit noise. Too slow and air and sediment sit. Steam is a different handbook table: steam velocities are measured in thousands of feet per minute, not a handful of feet per second.

45° offsets. When two parallel pipes are offset, two 45° elbows and a travel piece connect them:

(\text{Travel} = \text{Offset} \times 1.414)

A 12-inch offset needs about 17 inches of travel, center-to-center, before you subtract the two elbow takeoffs for cut length. Using 0.707 (cos 45°) converts travel back to offset; it does not give travel from offset. Rolling offsets add a third dimension; the handbook has the combined-offset table. Layout on the plan is centerline; fabrication is cut length after takeoff.

Valves, fittings, and sealants

Fittings include elbows, tees, couplings, unions, flanges, reducers, and dielectric unions where copper meets steel. Unions or flanges at equipment are a layout requirement so the coil or pump can come out without cutting the main.

Pipe-joint compound and PTFE tape seal tapered pipe threads (NPT). They do not belong on flared or compression refrigerant joints, gasketed flanges, press-connect joints, or soldered copper. Apply tape with the helix, typically two to three wraps, and keep it off the leading thread so shreds do not enter a control valve. Over-taping prevents the thread from making up to the handbook engagement length and can crack a fitting. Use a compound listed for the fluid. Yellow gas-rated tape is not a license to run new interior fuel lines: F.S. 489.105(3)(f) and (g) bar that work except appliance changeout disconnect/reconnect.

Piping plans and Florida layout

A piping plan shows size, service (CHWS/CHWR, HWS/HWR, condenser water, condensate, steam), valves, and equipment connections. Risers may be NTS. You still put isolation and unions at equipment, drains at low points, air vents at high points, slope on steam mains to drip legs and traps, expansion loops or compensators with guides and anchors, and hangers from the structure at handbook/spec spacing — not from duct or sprinkler mains. FBC Mechanical Chapter 3 still wants access and listed equipment. Coordinate with fire sprinklers; you do not relocate them (Section 18.4).

Florida scenario. A certified Class B shop in Lakeland bids a medical-office 15-ton chilled-water air handler. The coil is 180,000 Btu/h total at 10°F ΔT, so flow is (180{,}000 \div 5{,}000 = 36) gpm. The plan shows 1-1/4-inch mains, four 90° elbows, two isolation balls, a strainer, and a circuit setter. Class B may install that piping and the insulation — 489.105(3)(g) includes piping and insulation of pipes, vessels, and ducts. The same drawings also show a small hot-water boiler for reheat. That boiler and its unfired expansion tank, as boiler/pressure-vessel work, are Class A under 489.105(3)(f). The Class B qualifier sizes the chilled-water pipe from the handbook, uses the 500 constant, seals NPT with listed compound, and does not bid the boiler as a Class B change-order.