The Grid FriendlyTM Appliance (GFA) controller, developed at Pacific Northwest National Laboratory, was originallydesigned to autonomously switch off appliances by detecting under-frequency events. In this paper, the feasibility of usingthe GFA controller to provide primary frequency response is investigated. In particular, the impacts of an important designparameter, i.e., curtailing frequency threshold, on the primary frequency response are carefully analyzed for different situations. In the normal situation, the current method of selecting curtailing frequency thresholds for GFAs is found to be insufficient to guarantee the desired performance especially when the frequency deviation is shallow. In the extreme situations, the power reduction of online GFAs could be so excessive that it can even impact the system frequency negatively. As the first step towards the efforts to make GFAs suitable for providing primary frequency response, the existing controller design is improved by modifying the strategy of selecting curtailing frequency thresholds to ensure the effectiveness of GFAs in the normal situation.