306A Water Heating Systems 4 — Questions and Answers
Question 1: What is the purpose of a dip tube in a gas or electric storage water heater?
- To mix hot and cold water inside the tank
- To direct incoming cold water to the bottom of the tank so it does not cool the hot water at the top (Correct answer)
- To drain sediment from the tank
- To measure the water level in the tank
Correct answer: To direct incoming cold water to the bottom of the tank so it does not cool the hot water at the top
The dip tube extends from the cold water inlet at the top of the tank down to near the bottom, directing cold replacement water to the bottom where the heating element or burner is located. This maintains thermal stratification with hot water available at the top outlet.
Question 2: What is the typical lifespan of a standard residential storage water heater?
- 3 to 5 years
- 8 to 12 years (Correct answer)
- 15 to 20 years
- 25 to 30 years
Correct answer: 8 to 12 years
Standard residential storage water heaters typically last 8 to 12 years, depending on water quality, maintenance frequency (anode rod replacement, sediment flushing), and usage patterns.
Question 3: Why must a drain pan be installed under a water heater located in an attic or on an upper floor?
- To collect condensation from the flue
- To contain water from a leaking tank and direct it to a drain, preventing water damage to the structure below (Correct answer)
- To insulate the floor beneath the heater
- To provide a platform for the heater
Correct answer: To contain water from a leaking tank and direct it to a drain, preventing water damage to the structure below
A drain pan catches water from a leaking or overflowing water heater and directs it through a drain pipe to a safe discharge point, preventing costly water damage to ceilings, walls, and floors below.
Question 4: What is the recommended frequency for flushing sediment from a residential water heater?
- Monthly
- Every 6 to 12 months (Correct answer)
- Every 5 years
- Only when water pressure drops
Correct answer: Every 6 to 12 months
Sediment should be flushed from the tank every 6 to 12 months. In areas with hard water, more frequent flushing may be needed. Sediment buildup reduces heating efficiency and can damage the tank bottom.
Question 5: What is a 'condensing' water heater and why is it more efficient?
- It removes moisture from the water
- It extracts additional heat from the flue gases by cooling them below the dew point, recovering latent heat that would otherwise be lost (Correct answer)
- It operates at lower temperatures
- It uses thicker insulation
Correct answer: It extracts additional heat from the flue gases by cooling them below the dew point, recovering latent heat that would otherwise be lost
A condensing water heater uses a secondary heat exchanger to cool the flue gases below the dew point (approximately 55°C for natural gas). The water vapor in the exhaust condenses, releasing its latent heat into the water, achieving efficiencies above 90%.
Question 6: When installing a gas water heater in a confined space, how must combustion air be supplied?
- Through a standard HVAC duct
- Through dedicated air openings — one high and one low — connected to the outdoors or to a larger interior space (Correct answer)
- Through the flue pipe
- No special provisions are needed in Canadian homes
Correct answer: Through dedicated air openings — one high and one low — connected to the outdoors or to a larger interior space
A confined space requires two permanent openings — one within 300 mm of the ceiling and one within 300 mm of the floor — to provide adequate combustion air. These openings must connect to the outdoors or to a sufficiently large interior space.
306A Water Heating Systems 4
What is the purpose of a dip tube in a gas or electric storage water heater?