Ohio (OH) Hydronics Contractor Practice Exam Questions With Correct Solutions, Already Passed!!

1. A hydronic heating system’s expansion tank must be located on the _____ side of the circulator pump. A) Discharge B) Suction C) Bypass D) Return header after the last return connection Answer: B Explanation: The expansion tank should be installed on the suction side of the circulator to ensure that the pump sees a positive net positive suction head (NPSH) and to prevent cavitation. On the discharge side, the tank could cause erratic pressure changes and air binding. 2. In a primary-secondary hydronic system, the purpose of the secondary circulator is to _____. A) Overcome friction loss in the primary loop only B) Circulate water through the distribution system or zone independently of the primary loop C) Provide domestic hot water D) Act as a backup for the primary pump Answer: B Explanation: Secondary circulators create separate flow paths so that each zone or load can have its own flow rate without affecting the primary loop’s boiler flow. This allows for variable flow in secondary circuits while maintaining constant flow through the boiler.3. What minimum pipe size is typically required for a residential hydronic system’s boiler blow-off or drain valve per Ohio code? A) ½ inch B) ¾ inch C) 1 inch D) 1 ¼ inch Answer: B Explanation: Ohio Mechanical Code (based on IMC) typically requires a ¾-inch drain valve on a boiler to allow for proper flushing and maintenance. A smaller size may clog, and a larger size is not standard for residential boilers. 4. The maximum allowable working pressure (MAWP) for a low-pressure hydronic boiler, as defined by ASME Section IV, is _____. A) 15 psi steam / 30 psi water B) 30 psi steam / 50 psi water C) 15 psi steam / 160 psi water D) 50 psi steam / 100 psi water Answer: C *Explanation: ASME Section IV (Heating Boilers) defines low-pressure heating boilers as having MAWP not exceeding 15 psi steam or 160 psi water. Ohio adopts this standard for hydronic systems.* 5. The purpose of a thermostatic mixing valve in a hydronic heating system is to _____. A) Increase boiler efficiency by raising return water temperature B) Blend hot boiler water with cooler return water to prevent condensation in the boiler C) Separate air from the water D) Control zone valve operation Answer: B *Explanation: In condensing boilers, low return water temperatures cause flue gas condensation. A mixing valve (e.g., 4-way) blends supply water with return water to keep boiler inlet temperature above dew point, preventing corrosion and thermal shock.*6. A hydronic system’s air separator should be installed at the point where the water temperature is _____ and the velocity is _____. A) Highest, highest B) Highest, lowest C) Lowest, highest D) Constant, variable Answer: B Explanation: Air separators work best where water is hottest (air is less soluble) and velocity is lowest (allowing air bubbles to rise). This is typically at the boiler outlet before the circulator suction. 7. According to the Ohio Plumbing Code, a backflow preventer is required on the makeup water line to a hydronic boiler when _____. A) The system uses antifreeze B) The boiler pressure exceeds 30 psi C) There is a potential for chemical additives to backflow into the potable water supply D) The expansion tank is undersized Answer: C Explanation: Hydronic systems often contain corrosion inhibitors, glycol, or other chemicals. A reduced pressure principle backflow preventer (RPZ) or equivalent is mandatory to protect potable water from contamination. 8. What is the minimum recommended flow velocity in copper piping to prevent air accumulation? A) 1 ft/s B) 2 ft/s C) 4 ft/s D) 10 ft/s Answer: B *Explanation: A velocity of at least 2 ft/s helps sweep entrained air bubbles toward airseparators and vents. Below that, air can stagnate and form pockets, leading to noise and corrosion.* 9. In a series loop hydronic system, the temperature drop across each subsequent baseboard unit _____. A) Remains constant B) Increases C) Decreases D) Is irrelevant to heat output Answer: B Explanation: As water flows through baseboards in series, it loses heat. Each downstream unit sees cooler water, so the temperature drop between supply and return becomes larger relative to the room air temperature, reducing output per foot. 10. The Ohio Mechanical Code requires that a pressure relief valve on a hydronic boiler be _____. A) Rated at or below the MAWP of the boiler B) Set 50% above the boiler’s operating pressure C) Installed with a shutoff valve between the boiler and the relief valve D) Threaded directly into the boiler without a discharge pipe Answer: A Explanation: The relief valve’s set pressure must not exceed the boiler’s MAWP. Shutoff valves are prohibited between boiler and relief valve. Discharge piping must extend to within 6 inches of the floor. 11. A hydronic circulator operating with a closed discharge valve will likely experience _____. A) Reduced amp draw and possible cavitation B) Increased amp draw and rapid overheating C) No change in performance due to closed loop D) Immediate mechanical seal failure Answer: BExplanation: In a centrifugal pump, closing the discharge valve increases resistance, reducing flow. Power draw increases until near shutoff head, potentially overheating the motor and damaging the impeller. 12. The ideal pH range for water in a hydronic heating system with steel components is _____. A) 6.0 – 6.5 B) 7.0 – 8.5 C) 8.5 – 10.5 D) 11.0 – 12.5 Answer: C Explanation: Slightly alkaline water (pH 8.5–10.5) passivates steel surfaces, reducing corrosion. Acidic water (below 7) attacks steel; highly alkaline can cause caustic corrosion or gaskets failure. 13. A hot water boiler’s low water cutoff (LWCO) device must be installed _____. A) On the boiler supply piping at least 12 inches above the boiler B) At the lowest permissible water level point of the boiler C) On the return piping near the circulator inlet D) Anywhere in the system as long as it is above the boiler Answer: B Explanation: The LWCO must sense water level at or slightly above the boiler’s minimum safe water level (usually the top of the heat exchanger). Installing it too high causes nuisance shutdowns; too low risks overheating.