Water Heating Systems Flashcards
6 cards from real 306A practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Water Heating Systems flashcards as text
What is the purpose of a thermostatic mixing valve (TMV) on a water heater?
Answer: To blend hot and cold water to deliver a safe, consistent temperature to the distribution system while allowing higher storage temperatures
A TMV at the water heater outlet allows the tank to store water at 60°C (to prevent Legionella) while delivering tempered water at a safe 49°C or lower to the fixtures, protecting occupants from scalding.
What type of venting is used for a standard natural-draft gas water heater?
Answer: Type B double-wall metal vent pipe connected to a vertical chimney or vent
Standard natural-draft gas water heaters use Type B double-wall metal vent pipe, which connects to a vertical chimney or dedicated vent. The hot exhaust gases rise naturally through the vent due to buoyancy (natural draft).
What is the minimum distance a gas water heater's flue must be from combustible materials?
Answer: 150 mm (6 inches) for single-wall vent pipe
Single-wall vent pipe requires a minimum clearance of 150 mm (6 inches) from combustible materials. Type B double-wall vent requires only 25 mm (1 inch) clearance due to its insulated construction.
What is the function of the thermocouple in a gas water heater?
Answer: To generate a small electrical voltage when heated by the pilot flame, keeping the gas valve open as a safety measure
The thermocouple is a safety device that generates a small electrical voltage (millivolts) when heated by the pilot flame. This voltage holds the gas valve open. If the pilot goes out, the thermocouple cools, the voltage drops to zero, and the gas valve closes, preventing gas accumulation.
When replacing a water heater, what must be checked regarding the existing gas supply line?
Answer: The gas supply line size must be verified to ensure it can deliver adequate volume for the new heater's BTU rating, and the gas type must match
When replacing a water heater, the existing gas supply line must be verified to ensure it can deliver the required gas volume for the new unit's BTU input rating. An undersized gas line will cause incomplete combustion, sooting, and potentially dangerous carbon monoxide production.
What is the purpose of the drain valve at the bottom of a storage water heater?
Answer: To allow periodic draining of sediment from the tank and complete draining for maintenance or replacement
The drain valve allows the homeowner or technician to periodically flush sediment that accumulates at the bottom of the tank and to completely drain the tank for maintenance, repair, or replacement.