The topic of flexibility is gaining importance in the energy sector, including flexibility on the household level. Not only electrical storage but also heat pumps can provide the much-needed flexibility and can be pooled to participate in a number of electricity markets. The aim of this work is to determine the economic potential of the flexible use of heat pumps in single-family houses. For this, we use an example of the Austrian balancing market for manual frequency restoration reserve for a simulated pool consisting of 400 single-family houses with different thermal properties. Using a linear bottom-up optimization model, we identify a technically feasible flexibility range and achievable economic revenues, perform parameter variations, and examine various influencing factors. Building insulation, electric power of the installed heat pumps and the permitted room temperatures seem to have particularly significant effects on profitability. The greatest revenues can be achieved with existing buildings due to their higher heating load, followed by low-energy houses with air heat pumps. An additional storage tank has little influence on the flexibility potential. Most balancing energy can be offered in winter and autumn while in summer practically no market participation makes economic sense. Results further show that, depending on the building type, balancing power can be provided four to eight hours a day; a passive house in turn can offer up to twelve hours of service. With a heat pump and building distribution typical for Austria, it is possible to achieve 65-69 per heat pump on the balancing market for manual frequency restoration reserve in 2016. In order to obtain a positive business case, above all an affordable, standardized communication infrastructure is crucial.