|Where a domestic
hot water system has long runs of pipe with numerous bends, the friction
may be sufficient to prevent the normal and natural circulation of the
hot water. In these cases, a pump is often installed on the return end
of the system to supply the circulation.
The purpose of this pump is not to pump the water to the fixtures, but to circulate the water through the system fast enough so that when a faucet is opened, hot water may be almost instantly drawn. Therefore, this pump must have the capacity to move the water sufficiently fast to keep it from cooling.
The capacity of this pump is determined by the following rules and will ensure that a supply of hot water may always be available.
One gallon per minute for each twenty fixtures using hot water where hot water pipes are covered.The friction in a domestic hot water system is usually nominal (as compared to industrial systems), therefore the
head against which the pump must discharge will rarely exceed fifteen to twenty feet.
for Forced Hot Water Circulation at
Example: 1,000,000 BTU are being dissapated hourly and the temperature drop in the system is 15°F. The pump must therefore handle 150 US GPM.