Ferdinand Posted October 10, 2019 Share Posted October 10, 2019 (edited) Not really sure if this is sufficiently boffin-y. However... I am currently having my upstairs bathroom redone, and when we exposed the pipes supplying the whb, it turns out that the Hot is a 22mm pipe, and the Cold is a 15mm. This was built by a self-builder, and we were trying to fathom why this might be the case. My fitter commented that making it 22mm would probably result in a slower supply of hot water, and mentioned the Venturi effect. Plumbing and fluids not being my thing, can someone supply an explanation as to why this is the case (or a link), and why he may have done it? One impact of the new bath I have installed in addition to the shower is that there is now backwash up through the plughole of the downstairs shower (which has replaced a bath) and it now needs a non-return valve. What fun. Cheers F Edited October 10, 2019 by Ferdinand Link to comment Share on other sites More sharing options...
Carrerahill Posted October 10, 2019 Share Posted October 10, 2019 11 minutes ago, Ferdinand said: Not really sure if this is sufficiently boffin-y. However... I am currently having my upstairs bathroom redone, and when we exposed the pipes supplying the whb, it turns out that the Hot is a 22mm pipe, and the Cold is a 15mm. This was built by a self-builder, and we were trying to fathom why this might be the case. My fitter commented that making it 22mm would probably result in a slower supply of hot water, and mentioned the Venturi effect. Plumbing and fluids not being my thing, can someone supply an explanation as to why this is the case (or a link), and why he may have done it? One impact of the new bath I have installed in addition to the shower is that there is now backwash up through the plughole of the downstairs shower (which has replaced a bath) and it now needs a non-return valve. What fun. Cheers F People think you are supposed to use 22mm for hot as standard because they didn't understand the logic behind it on old non-pressurised tanked hot supplies. I still see people immediately reach for 22mm pipe when they are doing hot water piping even though they are on mains pressure via combi/sealed tank. So my guess is ignorance? 1 1 Link to comment Share on other sites More sharing options...
Vijay Posted October 10, 2019 Share Posted October 10, 2019 Is the hot supply from a hot water cylinder or combi/mains pressure, and cold from water tank or mains pressure. The only reason I can think of why he's done that is cold is on mains pressure? 1 Link to comment Share on other sites More sharing options...
Ferdinand Posted October 10, 2019 Author Share Posted October 10, 2019 (edited) 3 minutes ago, Vijay said: Is the hot supply from a hot water cylinder or combi/mains pressure, and cold from water tank or mains pressure. The only reason I can think of why he's done that is cold is on mains pressure? The hot is from a Combi. He has done a few other idiosyncratic things in various places. Its the swings of buying a self-build compared to the roundabout of a developer house ?. The structure is relatively over-engineered compared to the first fit, which is relatively skimped in some places. I put that down to "bugger - budget consumption is ahead of house production". F Edited October 10, 2019 by Ferdinand Link to comment Share on other sites More sharing options...
Carrerahill Posted October 10, 2019 Share Posted October 10, 2019 Just now, Ferdinand said: The hot is from a Combi. He has done a few other idiosyncratic things in various places. Its the swings of buying a self-build compared to the roundabout of a developer house ?. F Go 15mm then. There is even the discussion re. 10mm for basin supplies. Link to comment Share on other sites More sharing options...
Ferdinand Posted October 10, 2019 Author Share Posted October 10, 2019 (edited) 3 minutes ago, Carrerahill said: Go 15mm then. There is even the discussion re. 10mm for basin supplies. Er .. no. Will not be ripping out all the walls to replace pipes ?. The horror - have just upgraded both bathrooms. If necessary I will apply a pump instead. Edited October 10, 2019 by Ferdinand Link to comment Share on other sites More sharing options...
joe90 Posted October 10, 2019 Share Posted October 10, 2019 I agree with ignorance, plus the fact bath taps are usually 22mm pipe threads. My new bath is 15mm pipe feeds with reducers to 15mm pipe from a pressurised DHW tank and mains cold (reduced to 3bar) and the flow is very good. Link to comment Share on other sites More sharing options...
Carrerahill Posted October 10, 2019 Share Posted October 10, 2019 1 minute ago, Ferdinand said: Er .. no. Will not be ripping out all the walls to replace pipes ?. If necessary I will apply a pump instead. I was meaning for the refit part of your bathroom... Link to comment Share on other sites More sharing options...
Ferdinand Posted October 10, 2019 Author Share Posted October 10, 2019 Just now, Carrerahill said: I was meaning for the refit part of your bathroom... Cheers. Unfortunately it is behind tiles we are not refitting - had to create a one tile sized hole because the Ikea sink is different to a normal sink. F Link to comment Share on other sites More sharing options...
PeterW Posted October 10, 2019 Share Posted October 10, 2019 22mm hot is still in a lot of the text books - makes no sense as that was when gravity was king. Link to comment Share on other sites More sharing options...
Conor Posted October 10, 2019 Share Posted October 10, 2019 (edited) All things being equal, you get a higher flow rate through a 22mm pipe than a 15mm pipe. But in your case, the combi boiler won't be able to produce enough hot water to make use of the extra capacity in the pipe. When I did my bathroom, I ripped out all the old 1" copper and replaced with 15mm plastic. Venturi effect is something completely different. It describes how a sudden change in fluid velocity has a corresponding change in pressure.This is how those wine aerotors / guzzlers work. A small hole at a narrow point in the tube where you effectively have negative pressure, draws in air from the outside. Going back a century or so, this is how a lot of large water meters worked. The ratio of the lengths/diameters of two opposing cones would produce a predicted pressure change depending on the flow rate. So by measuring the upstream and downstream pressures, you could calculate the flow through the meter. Genius. http://hyperphysics.phy-astr.gsu.edu/hbase/Fluids/venturi.html Edited October 10, 2019 by Conor Link to comment Share on other sites More sharing options...
Ed Davies Posted October 10, 2019 Share Posted October 10, 2019 4 hours ago, Ferdinand said: My fitter commented that making it 22mm would probably result in a slower supply of hot water, and mentioned the Venturi effect. Anybody else think mention of the Venturi effect is a complete red herring here? 4 hours ago, Ferdinand said: Plumbing and fluids not being my thing, can someone supply an explanation as to why this is the case Just in case this isn't obvious to anybody, 22mm won't provide a slower supply of hot water (in litres/minute or whatever) once it's run through to hot but it'll take longer for the water to get hot at the tap when you first turn it on, compared with 15 or 10mm pipe, simply because there's a greater volume of cold water waiting in the pipe which has to be run through and replaced. 1 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now