Pipe sizes query

[cjard]

Several times over the years I've heard plumbers max reference to using larger pipes for better flow rates - running 22mm to the bathroom tap, for example. While I can accept that a larger pipe has a greater volume per surface area of internal bore (the inner surface being where friction/resistance to flow comes from) I'm not convinced that using a larger pipe (particularly for hot) gives you better performance, because the outlet is only going to have a certain size and all a larger pipe is going to do is give a larger standing volume of water that must be discharged through the outlet

In the case of hot water (not on a continually pumped circuit) there could be quite a considerable volume to get rid of - by my reckoning 10 metres of 22m pipe has nearly 4 litres of water in it - and that's not very eco friendly..

So when I'm looking at a quote saying 22mm copper for highest flow rates surely this is nonsense (aside from larger pipes having slower flow) and I should be saying to the plumber to use a smaller bore, or even plastic (lower friction, fewer elbows) or I should be finding another plumber who can accurately justify every pipe choice in terms of material and bore depending on the application?

 

[Dan Robinson]

I should be giving up if I were you as you have no idea.

Unless you are on a wind up.

 

[Hugh Jaleak]

The whole point of using 22mm pipe to a bath for example, is that 22mm (3/4") taps are of greater diameter to allow a faster flow. I certainly get more volume of water from my bath hot tap, (3/4" and fed with 22mm pipe), than I do the basin hot tap, (1/2" and fed with 15mm pipe)....

 

[Biggles..]

Ahhhhh, pressure vs flow....q TellyT and his static flow measurement/ dynamic flow measurement.

 

[cjard]

I should be giving up if I were you as you have no idea.

Unless you are on a wind up.

No, I seem to be looking at a plumbing quote to do everything in 22mm copper for "best flow rates".. which I think is a crock. Basin tap fed with 15mm vs basin tap fed with 22mm - same distance of piping from the same tap off point on the tank, let's say. Tell me Dan - which tap do I get more water out of in a minute? Which one takes longer to get warm?

 

[Dan Robinson]

The only thing in your opening post that is anywhere near accurate is the mention of pipe volume. But then most ten year olds can work out the volume of a cylindrical object.


As for the rest...... Are you suggesting a 10m run of, 10mm poly is going to give a higher flow rate than the same length of 22mm copper at a given pressure?

I think not. And as for plastic giving lower resistance than copper in general?

Hhhmmm.

 

[Dan Robinson]

do I get more water out of in a minute?

Are they the same taps?


I think not.

 

[Dan Robinson]

Which one takes longer to get warm?

A different issue entirely.

 

[MJGas]

I very much doubt he's going to take 22mm to the basin tbh...

 

[Dan Robinson]

Maybe - but imagine being his plumber?

 

[simond]

I think his original post was referencing the pointlessness of running big bore pipes to small bore HW outlets because of the wasted water.

And this is true, but it is also true that most punters want their bath to fill up quickly off a mains pressure system.

It clearly doesn't make financial sense in terms of pipe, nor is it a good idea from a notching floorboard and legionella risk viewpoint, to run separate ideal bore-matched pipes from the heat source to each outlet.

Especially in a simple domestic situation. Asking a plumber on a domestic to justify every pipe choice in terms of flow could result in a long wait for the quote to arrive, never mind the hot water - to put it politely.

 

[cjard]

do I get more water out of in a minute?

Are they the same taps?
.

Let's say they are.. That was rather the spirit of the query after all!

As for the length of time to get warm, it's not exactly a different issue, is it? The flow rate determines how long it takes to empty the standing water and deliver hot, and if you're making a case for larger diameter pipes having higher flow rates then it has a bearing on how long it takes to get warm..

Ultimately, I'm curious as to why a quote would even have a line like that on it, implying that 22mm copper is going to be used throughout for best flow rates..

 

[Dan Robinson]

Are you suggesting a 10m run of, 10mm poly is going to give a higher flow rate than the same length of 22mm copper at a given pressure?

 

[Dan Robinson]

For the record..... I have 22mm from softener to unvented cylinder safety group. Then 22mm from there to bathroom. Bath fills at 25 l/min.

Have 10mm tube from cylinder to utility room. Similar linear distance in the opposite direction without the 3 metre rise from ground to bathroom.


Do you want a crack at the flow rate to the utility tap (unfettered)?

 

[cjard]

justify every pipe choice in terms of flow could result in a long wait for the quote to arrive, never mind the hot water - to put it politely.

Yes, perhaps I shouldnt have said every pipe, like I was going to be asking for a detailed spec on each metre of pipe used.. The house was designed to minimise pipe runs because the missus can't stand waiting ages for the hot to come through, so most taps can probably be plumbed in less than 5 metres of pipe fm the storage tank/heat source. I'd imagine that most taps would be fed via a dedicated pipe run simply because he arrangement of the house is such that here isn't really a loop or branch layout that would use less pipe than a point to point.. Apart from one ensuite that is above the bathroom that is above the utility

So really the query was about the implication that using bigger pipes was better for flow rates(possibly it is) but surely worse for reaction times (which the wife is far more likely to care about, than whether a tap can deliver 10 litres a minute)