There are a few potential reasons why your new furnace may take several minutes or longer to turn on after adjusting the thermostat:
Pre-heating period: Some modern furnaces have a built-in pre-heating period before they start blowing warm air. This pre-heating helps ensure that the air coming out of the vents is already warm, providing more immediate comfort. During this period, the furnace is warming up to its optimal operating temperature before starting to distribute heated air.
Thermostat calibration: The new thermostat may have different calibration settings compared to your old one. It could have a wider temperature differential or a different algorithm for determining when to turn the furnace on or off. This can lead to a delay in activating the furnace when adjusting the temperature.
Furnace ignition process: Modern furnaces might have more complex ignition systems, such as hot surface igniters or electronic ignition, which can take a little longer to ignite the burners and start the heating process compared to older furnaces with a pilot light.
System efficiency settings: Newer furnaces often come with energy-saving features that help improve efficiency. Some models may have a delayed start to optimize energy consumption and avoid frequent cycling on and off, especially if the temperature change is minor.
Air distribution: It's also possible that the ductwork or air distribution system has been modified during the furnace replacement. Changes in the duct design or size can affect the time it takes for warm air to reach the vents and circulate throughout the house.
Furnace size and capacity: If the new furnace has a different heating capacity or size compared to the old one, it might require more time to reach the desired temperature and activate the blower.
Unless there is a significant delay or if you notice any unusual behavior with your new furnace, a slight delay in turning on may be normal. However, if you have concerns about the furnace's performance or operation, it's best to contact the company or technician who installed the furnace to have it inspected to ensure everything is working correctly. They can also help address any specific questions or issues related to your particular furnace model and thermostat.