What is the minimum pipe size for a pumped primary circuit to an open vented hot water storage vessel?

For a pumped primary circuit to an open vented hot water storage vessel, the minimum pipe size typically recommended is 22mm. This size is chosen to ensure that there is enough flow rate to adequately circulate water, which is crucial for maintaining the efficiency of the hot water system.

Using a larger diameter pipe like 22mm helps to minimize resistance and pressure drops within the system, allowing for smoother water flow from the heat source to the storage vessel. This is important in ensuring that the water is heated effectively and transferred to the storage vessel without significant delays or issues.

Additionally, a 22mm pipe is often deemed adequate for the volume of water that needs to be circulated, especially in residential applications, while still being manageable in terms of installation. Utilizing a smaller diameter pipe could potentially restrict flow, leading to inadequate heating and increased wear on the pump due to higher pressure requirements.