What does the pressure switch on an induced-draft furnace prove before ignition is allowed?
- That the gas supply pressure at the valve inlet is high enough
- That the circulating blower is moving air across the heat exchanger
- That the air filter is clean enough for the furnace to run safely
- That the inducer is moving air through the heat exchanger and vent
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D. That the inducer is moving air through the heat exchanger and vent
The switch senses the negative pressure created by the draft inducer, confirming that combustion air is flowing and the vent is not blocked. It does not measure gas pressure, despite its name.
Reference: Appliance manufacturer installation and service instructions
About how many cubic feet of air are needed to completely burn one cubic foot of natural gas?
- 2 cubic feet
- 5 cubic feet
- 10 cubic feet
- 24 cubic feet
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C. 10 cubic feet
Natural gas needs about 10 cubic feet of air per cubic foot of gas for complete combustion. About 24 cubic feet is the figure for propane, which has more carbon and hydrogen in each cubic foot.
Reference: Combustion fundamentals; NFPA 54 Annex
Which of these materials is not permitted for fuel gas piping under the IFGC?
- Schedule 40 steel pipe
- Cast-iron pipe
- Corrugated stainless steel tubing
- Polyethylene pipe underground
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B. Cast-iron pipe
Cast-iron pipe is specifically excluded from gas piping. Steel pipe, listed CSST and polyethylene (outdoors, underground) are all recognized materials.
Reference: IFGC 2021 Section 403; NFPA 54 Section 5.6.2