Patent ID: 7392661

Claim:
A method whereby an HVAC controller estimates a change in energy usage by an HVAC system controlled by the HVAC controller, the method comprising: maintaining a baseline energy usage for a current HVAC system setting including a condition-to temperature; changing the HVAC system setting in response to input from a user of the HVAC controller; maintaining a table indicating one of an estimate of degree-hours which a local climate will be above a temperature in a temperature range and an estimate of degree-hours which the local climate will be below a temperature in a temperature range; estimating a new energy usage for the changed HVAC system setting, including, looking up the condition-to temperature in the table of estimated degree-hours to determine a number of degree-hours of conditioning which the HVAC system will operate to maintain the condition-to temperature, calculating a cost of operating the HVAC system for the determined number of degree-hours, and determining a difference between the calculated cost and a previously stored cost; and displaying to the user an indication of a difference between the estimated energy usage and the baseline energy usage.