In this work, two indirect approaches are compared to estimate the efficiency of the cold metal transfer welding process with two different current waveforms. The first approach is based on an analytical heat transfer model coupled with thermocouple measurements. The second method includes numerical heat transfer simulation of aluminium filler on the galvanised steel sheet. Then a diffusional-growth model allows evaluating the thickness of the Fe-Al intermetallic layer that was compared it to that of the experimental one. Results show that both methods give very similar process efficiencies. The process efficiency reaches a high value (0.92) with current wave-forms using high-intensity pulses of short duration, whereas it decreases to 0.78 with current waveforms using low-intensity pulses of long duration.