A thermostat is described for controlling air temperature in a building. The time associated with causing the controlled air temperature to reach a target temperature is estimated and displayed to a user. Input from a user indicating the target temperature can be received and the estimating and displaying can be carried out in real time. The thermostat can be wall-mounted or the user input can be received and estimated time can be displayed using a remote device, for example that communicates wirelessly with other components of the HVAC system.