The purpose and novelty of this work was to evaluate both the total and the transient energy efficiency of three types of modern wood stoves based on experimental results at different loads and elaborate on the level of energy efficiency increase that can be achieved by improved stove operation (user-controlled) and control (by design or automation). The experimental results show that the energy efficiency for modern wood stoves is around 80%, which is much higher than for old wood stoves due to improved stove designs and better combustion process conditions. This gives much reduced emission levels, contributing to a higher combustion efficiency, improved mixing conditions reducing the excess air need and improved heat exchanger designs reducing the chimney inlet temperature, both increasing the thermal efficiency. However, there is a significant improvement potential through further improved combustion control and stove operation, reducing the negative effects on emissions and efficiencies of the crucial period after igniting a new batch and in the final part of the char burnout. Improved heat exchanger designs and increased heat storage capacity will further increase the thermal efficiency. The total (stove) efficiency has the potential to approach the efficiency of pellets stoves.