Xiaoying Li, Södertörn University, will present the study "Tap gap: energy performance gap and rebound effects of hot water use in the Soviet-era multi-apartment buildings", co-authored with Andrius Kažukauskas, Vilnius University.

Retrofits of Soviet-era dwellings play an important role for post-Soviet countries in dealing with energy security and climate issues. One essential question is whether retrofits can deliver energy savings that are promised by the engineering model. The paper measures the energy performance gap - the discrepancy between realized energy savings for space heating and hot water and the predictions by engineers in the retrofit program of multi-apartment buildings in Lithuania. The results show performance gaps ranging from 47% to 69%, with larger gaps for energy-efficient buildings after the retrofit.

The study explores whether the gap can be explained by the rebound effects in energy use in multi-apartment buildings. The results suggest a limited rebound effect in the use of space heating but a larger effect in the use of hot water. Here, the rebound effect results in an increase in hot water use following energy efficiency improvements. This effect is especially large the first two years after the retrofit.

The authors argue that their findings on the performance gap and the rebound effect for hot water use generate implications for the design of the new retrofit program in the post-Soviet countries.