> Or is the rate based on the difference between inside and outside temperature?
Both conductive heat loss and "air leak" heat loss is dependent upon the temperature difference between inside and outside temperature.
For conductive loss, the heat differential determines the amount of heat that "moves" per unit time from the hot side to the cold side.
For "air leak" heat loss, the temperature difference between outside and inside determines the amount of "heat" lost/gained by the leaks per unit time (assuming the leaks are constant).
Are both "linear"? To a first order approximation they are probably "linear enough" to treat them as "linear" given your use case (lower/raise interior temp when no one is home). But also consider that the greater the raise/lower, the longer any recovery will take, so consider than in your calculations as well.
Both conductive heat loss and "air leak" heat loss is dependent upon the temperature difference between inside and outside temperature.
For conductive loss, the heat differential determines the amount of heat that "moves" per unit time from the hot side to the cold side.
For "air leak" heat loss, the temperature difference between outside and inside determines the amount of "heat" lost/gained by the leaks per unit time (assuming the leaks are constant).
Are both "linear"? To a first order approximation they are probably "linear enough" to treat them as "linear" given your use case (lower/raise interior temp when no one is home). But also consider that the greater the raise/lower, the longer any recovery will take, so consider than in your calculations as well.