Artificial injections of SO₂ into the tropical stratosphere show an impact on the quasi-biennial oscillation (QBO). Different numerical models show only qualitatively but not quantitatively consistent impacts. We show for two models that the response of the QBO is similar when a similar stratospheric heating rate is induced by SO₂ injections of different amounts. The reason is very different vertical advection in the two models resulting in different aerosol burden and heating of the aerosols.