Heating Systems Flashcards
7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Heating Systems flashcards as text
Which heating system type is best suited for a building where individual room temperature control and zoning flexibility are the top priorities?
Answer: Electric resistance baseboard heaters with individual thermostats per room
Electric resistance baseboards with individual thermostats offer the most granular room-by-room control with no shared ductwork or piping constraints.
A gas furnace's inducer motor runs but the igniter does not glow. The control board has power. What is the most likely cause?
Answer: Tripped high-limit switch or failed pressure switch preventing the board from advancing the sequence
After the inducer runs, the control board waits for pressure switch confirmation before energizing the igniter; a stuck or failed pressure switch halts the sequence at that step.
What is the purpose of a modulating gas valve in a variable-capacity furnace?
Answer: To continuously vary the gas firing rate between minimum and maximum to match heating demand
A modulating gas valve adjusts firing rate continuously (e.g., 40–100% of capacity), improving comfort and efficiency by matching output closely to the actual heating load.
When retrofitting a new high-efficiency condensing furnace to an existing chimney-vented system, what must the technician do with the chimney?
Answer: Abandon the chimney for flue venting and run PVC vent pipes directly through a wall or roof
Condensing furnaces produce cool, moist flue gases unsuitable for masonry chimneys; they require PVC or CPVC direct vent piping routed through an exterior wall or roof.
In a heat pump heating mode, at what outdoor temperature does the system's COP typically drop to approximately 1.0, making it no more efficient than electric resistance heat?
Answer: 17°F (-8°C) to 0°F (-18°C), depending on the system
Most standard air-source heat pumps reach a COP near 1.0 between 0°F and 17°F, below which auxiliary electric strip heat becomes the primary heat source.
What type of pipe is required for the condensate drain on a 96% AFUE condensing gas furnace?
Answer: Schedule 40 PVC or CPVC rated for acidic condensate
Condensate from high-efficiency furnaces is mildly acidic (pH 3–4) and should be drained with PVC or CPVC; metal pipes corrode and must be avoided.
A technician performs a combustion analysis and finds the CO2 reading in the flue is 12% for a natural gas furnace. What does this indicate?
Answer: A near-stoichiometric air-fuel ratio indicating efficient combustion
For natural gas, peak theoretical CO2 is about 12%; readings of 10–12% CO2 combined with low CO indicate good combustion efficiency.