The ability of manual metal arc welders to reach target heat input (HI) values between 1.3 kJ/mm and 2.9 kJ/mm by varying weld travel speed was examined. Weld process data was collected during the downhand and overhead welding of 6 highly restrained quenched and tempered (QT) steel plates and the results showed that the measured average H I values were closely matched to the target HI. However, there was considerable scatter, particularly at higher H I targets, which warranted investigation. The frequency at which welders achieved their target H I (or travel speed) decreased at higher H I values, but nonetheless the standard deviation (SD) from the average HI was less than 10% for all target HI values, which is well within the average 15% deviation allowed for a qualified weld in the Australian Pressure Vessel Standard, AS3992-1998. The effect of localised variations in voltage on H I was also considered. Even though voltage fluctuated by as much as 40% during the deposition of an electrode, the overall impact on arc energy H I was considered negligible because of the short duration at these ‘extreme ’ voltages. Moreover, it was found that the levels of diffusible hydrogen marginally decreased as H I increased, which lends support to the fact that HI is a contributor to weldment cooling rate. Additionally, differences in microstructure and hardness were also observed between low (1.3 kJ/mm) and high (2.9 kJ/mm) HI values in the diffusible hydrogen test (bead on plate) samples.