A single stage furnace will deliver the same amount of heat and airflow no matter what the temperature is outside. A 2-stage furnace with a 2-stage thermostat will begin in first stage (low burner, low airflow) and only go to second stage if the indoor temperature drops during first stage. This makes the furnace run longer, providing greater air circulation, temperature distribution, and air filtration. This also provides a more consistent indoor environment. The second stage will only come on when the need is there and then it will be able to run longer and maintain the comfort level. The more your system starts and stops, the less control you will have of your home’s environment – and the less efficiently it works, partly due to duct heat loss. The advantage of Trane’s 2-stage, variable-speed furnace is it has Comfort-RT Enhanced mode. This allows the coil to cool quickly and the blower to slowly ramp up and ramp down or operate at 50 percent of the cooling air speed in the FAN ON position. This provides greater humidity control, quieter operation, and maximum air circulation, temperature distribution, and air filtration.