What condition can result from high velocity in an undersized heating main?

High frictional losses occur in a heating system when there is high velocity in an undersized heating main. This is primarily due to the fact that as fluid moves through a pipe, it encounters resistance, and if the pipe is not adequately sized to accommodate the volume and velocity of the fluid, the friction between the fluid and the pipe's interior surfaces increases.

As the flow increases but the pipe diameter does not, the fluid must travel faster to maintain the required flow rate. This leads to turbulent flow, which enhances frictional losses significantly. Consequently, more energy is required to maintain the flow, negatively impacting the system's overall efficiency.

In contrast, options that suggest improved energy efficiency, better heat distribution, or decreased noise levels are contrary to the reality of high friction in an undersized system. Increased friction typically leads to less efficient operation and can result in other complications such as noise from the movement of the fluid.