Answer: 1/3 horsepower
Explanation: The most commonly installed horsepower for a sump pump is typically 1/3 horsepower. This horsepower is sufficient for the majority of residential applications, providing adequate pumping capacity without being overly powerful or energy-intensive. However, the appropriate horsepower for a sump pump can vary depending on factors such as the size of the home, the amount of water the pump is expected to handle, and the specific requirements of the installation.