NATE Hydronics Oil flashcards
NATE Hydronics Oil · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Sensible heat formula
- BTUH = 500 × GPM × ΔT for water, where 500 combines water density, 60 minutes per hour, and specific heat. Use 485 for 30% glycol and about 450 for 50% glycol.
- Static pressure rise
- Water exerts 0.433 psi per foot of height. A fill point 20 feet below the top of a loop must supply at least 8.66 psi plus 4 psi margin to keep the top flooded.
- Series loop system
- A piping arrangement where all emitters are connected in one continuous loop. Full flow passes through every emitter, so the last unit receives the coolest water and total flow is fixed.
- Reverse return piping
- A two-pipe layout where supply and return run in opposite directions, making the water path length nearly equal for every emitter. This self-balances flow without balancing valves.
- Net stack temperature
- Flue gas temperature minus combustion air temperature. Higher net stack temperature means more heat is leaving the boiler up the chimney, lowering steady-state efficiency.
- Excess air for No. 2 oil
- Theoretical air is about 14.4 pounds per pound of oil. Oil burners typically run 12 to 15 percent excess air, giving 5 to 8 percent CO2 in the flue gas.
- Nozzle flow versus pressure
- Nozzle GPH ratings are stated at 100 psi and flow changes with the square root of pressure. A 1.00 GPH nozzle at 140 psi flows about 1.18 GPH.
- Electrode gap setting
- Oil burner electrodes are typically set at a 1/8 inch gap with tips 1/16 to 1/8 inch ahead of the nozzle face. Wrong gap causes delayed ignition or puffback.
- Cad cell resistance
- A cadmium sulfide flame detector drops below roughly 400 to 600 ohms when flame is present. Resistance above about 1,600 ohms signals no flame and the primary control locks out.
- Overfire draft
- The negative pressure measured in the combustion chamber. Natural draft oil boilers commonly run minus 0.02 to minus 0.04 inches water column to pull flue gases out.
- Smoke number target
- A smoke test reading of 0 to trace (1) is the goal for No. 2 oil. Higher smoke means incomplete combustion from poor atomization, low draft, or too little air.
- Aquastat high limit
- The safety setting that shuts off the burner when boiler water reaches the setpoint, typically 180 to 200 degrees Fahrenheit. It is a series safety device and must never be bypassed.
- Oil primary lockout
- If the cad cell does not prove flame within 15 to 45 seconds, the primary control closes the oil valve and locks out. Most modern primaries require manual reset.
- Low-water cutoff
- A safety control that stops the burner if boiler water drops below a safe level. Required on steam boilers and on hot water boilers above 400,000 BTUH input.
- Circulator hold-off
- A control feature that delays the circulator until boiler water reaches a set temperature. It reduces cold-start condensation and thermal shock in oil-fired cast iron boilers.
- Combustion air openings
- Confined spaces need two permanent openings sized per NFPA 31, and unconfined spaces need roughly 50 cubic feet per 1,000 BTUH input. Starved burners produce soot and carbon monoxide.
- Zone valve end switch
- A switch inside the zone valve that closes when the valve opens, completing the circuit to the circulator or boiler T-T terminals. Its rating must match the circulator load.
- Baseboard output per foot
- Copper fin-tube baseboard delivers roughly 550 to 600 BTUH per linear foot at 180 degrees Fahrenheit average water temperature and about 4 GPM flow.
- Pump head calculation
- Head in feet equals friction loss per 100 feet times total equivalent length divided by 100. Add 2 to 4 feet for each fitting, valve, or boiler in the circuit.
- Primary/secondary piping
- Boiler loop and system loop are joined by closely spaced tees, decoupling flow. Primary flow must exceed secondary flow to prevent temperature blending at the tees.
- Expansion tank sizing
- Acceptance volume must cover system water volume times the expansion factor. Diaphragm tanks are precharged to fill pressure; bladder tanks are not and must be charged on site.
- Air separator location
- Install an air scoop or spirovent at the boiler supply where water is hottest and pressure is lowest. Provide at least 12 to 18 inches of straight pipe upstream.
- Pump operating point
- The point where the pump curve crosses the system curve. Throttling a valve steepens the system curve, moving the point up the pump curve with less flow and more head.
- Glycol flow correction
- Glycol has lower specific heat and higher viscosity than water, so flow must increase and pump head rises. Use 485 in the heat formula for 30 percent glycol and about 450 for 50 percent.
- Combustion test sequence
- Check draft first, then smoke, then CO2 or O2, then stack temperature. Adjust the air shutter for 0 to 1 smoke, then recheck draft and record all readings.
- Puffback cause
- Delayed ignition lets oil accumulate in the chamber before it lights, causing a puffback. Common causes are worn electrodes, wrong gap, dirty nozzle, or excessive oil before ignition.
- Oil pump vacuum reading
- A vacuum gauge on the pump inlet above 10 inches of mercury indicates a restricted oil line, clogged filter, or excessive lift. Correct the supply before adjusting pump pressure.
- Relief valve discharge
- The relief valve outlet must terminate 6 to 12 inches above the floor or to a safe drain. Never cap, plug, or reduce the outlet because the valve protects against overpressure.
- Air-free CO reading
- Flue gas carbon monoxide above 100 ppm air-free signals a combustion problem. Check for a blocked flue, soot, or improper draft before leaving the job.
- System fill pressure
- Cold fill pressure equals static head plus 4 psi margin at the top of the loop. A typical two-story residence is filled to 12 to 15 psi cold.
- Two-pipe oil line
- Required when the tank is below the burner or lift exceeds about 8 feet with a single line. The return line bleeds air and stabilizes pump pressure.
- Annual oil boiler service
- Replace the nozzle and oil filter, clean the heat exchanger and flue, check electrodes, test the cad cell, and verify draft, combustion, expansion tank charge, and relief valve operation.