Which device delays the furnace blower startup to increase efficiency?

• A. Delay timer
• B. Thermostat
• C. Time-delay relay
• D. Blower relay

Answer: (C)

The device is used to sequence the furnace start-up so air isn’t blown before the heat exchanger is warm, which improves heat transfer and overall efficiency. After the burner lights, the time-delay relay holds the blower off for a short, preset interval. Once that delay expires and the heat exchanger is hot enough, it energizes the blower circuit to start circulating conditioned air. This delay reduces delivering cold air and minimizes heat loss up the flue, making the system more efficient. The thermostat only signals demand for heat, and the blower relay simply switches the blower on or off; they don’t impose the startup delay by themselves. A delay timer could provide a delay, but the standard control element that provides this startup timing in furnace controls is the time-delay relay.