USA
Technical Q&A - How are low-flow areas created, and are they common?
Very often you find that, depending on how the system is plumbed, low-flow areas are created where new parts have been added to a system. For example, where you have an extension of the system into an addition on the home.
Frequently, the extension contains “dead legs.” For example, if you build a ground-floor extension onto a home or building where you have radiators, you would ideally want to plumb from the downstairs pipework. But if you have a solid floor, sometimes in order to avoid digging up that floor, the contractor will come up to the first level, and lift up some floor boards to access the pipework directly beneath. Then he’ll plumb it from the first floor back down to the ground floor, creating a drop in the heating system. The pipe will go down and then feed that radiator, and then it will go back up and reconnect to the first floor pipe works.
It is incredibly difficult to clean out that section, and you would need a very high head of pressure in order to push any debris down the pipe, and then back up the pipe and out the drain. This type of scenario can occur in commercial and residential installations.
In addition to these engineered low-flow areas, radiators and baseboards — by the nature and intent of their designs — slow the flow of system water, so these are natural low-flow areas where iron oxide can collect and cause problems.