QUB is an innovative method enabling the experimental measurement of the total heat loss coefficient (HLC) of a building envelope in one night only. It is based on a simple theory, yet can be demonstrated to be accurate even in a short time and in real buildings, as long as certain experimental conditions are fulfilled. This study combines analytical and numerical approaches to exactly solve the temperature response of an equivalent building submitted to a QUB test. This allows understanding that even with a short time experiment (less than a night), a reasonable accuracy on the estimated HLC can be obtained. The experiment has to be designed following a simple heating power criterion. Calculation is then tested experimentally in various cases whether in climate chamber or in real field, and whether on light weight/not insulated building or a heavy weight/highly insulated building. Results show that the QUB method performed by fulfilling this criterion is a promising method to estimate the HLC of a real building in the field with a reasonable accuracy in one night. (C) 2018 Elsevier B.V. All rights reserved.