Heat loss/resistance in CH system

[John Rumm]

Flow resistance is proportional to both the pipe internal diameter, and also the length of the pipe. So a short run of smaller diameter pipe will have less effect than a longer one.

The rate of heat "loss" in the rad will depend on its temperature and surface area, plus a bit on the ambient temperature in the room.

So as long as the flow of water can deliver heat at or above that rate, then you would expect no difference in performance.

You can basically ignore them...

The boiler circulators are deigned to cope with most likely pipework arrangements.

[Roger Hayter]

For the sake of future readers who may know that you are an expert, I take it you are using "proportional" in the colloquial sense of "depends on". As you know. it is actually proportional to quite a high power of the internal diameter, the exact relation depending on whether there is any turbulence.

[Roger Hayter]

Since I'm doing corrections, I suppose it's reciprocal resistance, flow per unit pressure rather then pressure per unit flow, that goes up with diameter!

[John Rumm]

Perhaps proportional is a poor choice of word since that normally implies that you can swap in an equal sign and a constant and you have yourself an equation. The influences on flow resistance are more complex than simple variables than you rightly state. Perhaps flow resistance would be better described as a function of pipe length and diameter and other variables. :-)

The thrust of what I was getting at was, yes a reduction in diameter will restrict flow, however a very short length reduction in diameter will have much less effect than a longer run at the same smaller diameter. So using a pipe insert that reduces a nominal 15mm^2 to 10mm^2 for 20mm will not be anything like as "damaging" as a 5m run of 10mm^2 micorbore pipe.