A method for determining the heat loss coefficient K of a premises, characterized in that it comprises steps in which: - there is undertaken, in the premises, over two successive time periods D 1 and D 2: i. over the first time period D 1, the application of a first heating power P 1 of the premises, and a campaign of measurements of at least one temperature inside the premises T i 1 at closely-spaced time intervals, as well as the determination of the temperature of the outside air T e 1 at closely-spaced time intervals, the first heating power P 1 being such that the parameter α = 1 − Δ T 1 0 K ref P 1 is less than or equal to 0.8 with ΔT 1 = T i 1 ( t =0) - T em, where t = 0 is the starting point of the first time period D 1, T em is the average temperature of the outside air over all of the time periods D 1 and D 2, and K ref is a reference value of the heat loss coefficient K of the premises determined on the basis of the heat transfer coefficient of the envelope of the premises obtained according to the standard ISO 13789:2007, and then ii. over the second time period D 2, the application of a substantially zero second heating power P 2 of the premises, and a campaign of measurements of at least one temperature inside the premises T i 2 at closely-spaced time intervals, as well as the determination of the temperature of the outside air T e 2 at closely-spaced time intervals; - for each of the first and second time periods D 1 and D 2, a time interval Δ t 1 or Δ t 2 is selected for which the evolution T i 1 ( t) or T i 2 ( t) is substantially linear, where the time intervals Δ t 1 and Δ t 2 are such that the time interval Δ t 1 extends up to the end of the first period D 1 of application of the first heating power P 1 and such that, when the starting points of the first period D 1, and of the second period D 2 are superimposed, the time intervals Δ t 1 and Δ t 2 have the same end point; - the slope a 1 or a 2 of the tangent to the curve ( T ik ( t)) k = 1 or 2 over each time interval Δ t 1 or Δ t 2 is determined; - the value K calc of the heat loss coefficient K of the premises is deduced on the basis of the slopes a 1 and a 2. - there is undertaken, in the premises, over two successive time periods D 1 and D 2: i. over the first time period D 1, the application of a first heating power P 1 of the premises, and a campaign of measurements of at least one temperature inside the premises T i 1 at closely-spaced time intervals, as well as the determination of the temperature of the outside air T e 1 at closely-spaced time intervals, the first heating power P 1 being such that the parameter α = 1 − Δ T 1 0 K ref P 1 is less than or equal to 0.8 with ΔT 1 = T i 1 ( t =0) - T em, where t = 0 is the starting point of the first time period D 1, T em is the average temperature of the outside air over all of the time periods D 1 and D 2, and K ref is a reference value of the heat loss coefficient K of the premises determined on the basis of the heat transfer coefficient of the envelope of the premises obtained according to the standard ISO 13789:2007, and then ii. over the second time period D 2, the application of a substantially zero second heating power P 2 of the premises, and a campaign of measurements of at least one temperature inside the premises T i 2 at closely-spaced time intervals, as well as the determination of the temperature of the outside air T e 2 at closely-spaced time intervals; i. over the first time period D 1, the application of a first heating power P 1 of the premises, and a campaign of measurements of at least one temperature inside the premises T i 1 at closely-spaced time intervals, as well as the determination of the temperature of the outside air T e 1 at closely-spaced time intervals, the first heating power P 1 being such that the parameter α = 1 − Δ T 1 0 K ref P 1 is less than or equal to 0.8 with ΔT 1 = T i 1 ( t =0) - T em, where t = 0 is the starting point of the first time period D 1, T em is the average temperature of the outside air over all of the time periods D 1 and D 2, and K ref is a reference value of the heat loss coefficient K of the premises determined on the basis of the heat transfer coefficient of the envelope of the premises obtained according to the standard ISO 13789:2007, and then ii. over the second time period D 2, the application of a substantially zero second heating power P 2 of the premises, and a campaign of measurements of at least one temperature inside the premises T i 2 at closely-spaced time intervals, as well as the determination of the temperature of the outside air T e 2 at closely-spaced time intervals; - for each of the first and second time periods D 1 and D 2, a time interval Δ t 1 or Δ t 2 is selected for which the evolution T i 1 ( t) or T i 2 ( t) is substantially linear, where the time intervals Δ t 1 and Δ t 2 are such that the time interval Δ t 1 extends up to the end of the first period D 1 of application of the first heating power P 1 and such that, when the starting points of the first period D 1, and of the second period D 2 are superimposed, the time intervals Δ t 1 and Δ t 2 have the same end point; - the slope a 1 or a 2 of the tangent to the curve ( T ik ( t)) k = 1 or 2 over each time interval Δ t 1 or Δ t 2 is determined; - the value K calc of the heat loss coefficient K of the premises is deduced on the basis of the slopes a 1 and a 2.