Plumbing question

[teaky]

Yes, I know this is a railway modelling forum but there are electricians on here so there may be plumbers too.

 

As a result of having the boiler changed to a combi a few years ago, I now have a 15mm pipe running up from the airing cupboard into the loft where it splits into two.  One run feeds an en-suite shower and the other feeds the bathroom bath/shower.  Just after the pipes divide the bathroom feed changes to 22mm.  (I have no idea why this should be.  There may be a reason or it may simply be that the boiler installer only had enough 22mm in his van.)

 

My question is: if I change the 22mm pipe to 15mm will it have any effect on the water pressure in the bathroom?

 

[Robert]

It shouldn't do - because the feed to the point where it splits is 15mm.  That means that both sides of the T-piece are fed with the same 15mm pipe.

 

Maybe the reason for the 22mm pipe is that it was part of the original installation?

 

I should add, I am not a plumber - However, I am sure one will be along soon!

[teaky]

It shouldn't do - because the feed to the point where it splits is 15mm.  That means that both sides of the T-piece are fed with the same 15mm pipe.

 

Maybe the reason for the 22mm pipe is that it was part of the original installation?

 

I should add, I am not a plumber - However, I am sure one will be along soon!

Thanks Robert.

 

I suspect that is the case.  I didn't pay too much attention to the original plumbing arrangements.  It all looked standard and everything worked, so why nose around?  The pipes in the loft are encased in foam insulation, so you cannot see what the pipe diameter is until you remove this.  Originally these two pipe would have come from the cold water cistern and the feed pipe would have topped up the cistern as required.  The bathroom tap is a large Victorian style mixer with a shower head that either sits in a cradle or slots into a bracket on the wall.  It has quite a large outlet so maybe the 22mm was put in to increase the flow rate.

 

I am expecting the answer to be that it makes no difference because the feed is 15mm, just as you say, but thought there was no harm in double checking since my plumbing knowledge does not extend beyond 'straightforward domestic'.

[APOLLO]

Yes, I know this is a railway modelling forum but there are electricians on here so there may be plumbers too.

 

As a result of having the boiler changed to a combi a few years ago, I now have a 15mm pipe running up from the airing cupboard into the loft where it splits into two.  One run feeds an en-suite shower and the other feeds the bathroom bath/shower.  Just after the pipes divide the bathroom feed changes to 22mm.  (I have no idea why this should be.  There may be a reason or it may simply be that the boiler installer only had enough 22mm in his van.)

 

My question is: if I change the 22mm pipe to 15mm will it have any effect on the water pressure in the bathroom?

 

It could do. All fluids (both gas & water) flowing through a pipe undergo a drop in pressure from start to finish. This pressure drop can be reduced by enlarging the pipe diameter. In your case the first pipe run is 15mm, then changes to a larger 22mm dia. This seems a little odd - it's usually the other way round !!. However changing the last bit by reducing the diameter from 22mm to 15mm MAY increase the pressure drop resulting in a smaller flow.

 

If all is well now - leave it as is. If you need a little more flow upsize some / all the 15mm to 22mm. I would be inclined to leave it all alone if it works OK.

 

Brit15

[teaky]

It could do. All fluids (both gas & water) flowing through a pipe undergo a drop in pressure from start to finish. This pressure drop can be reduced by enlarging the pipe diameter. In your case the first pipe run is 15mm, then changes to a larger 22mm dia. This seems a little odd - it's usually the other way round !!. However changing the last bit by reducing the diameter from 22mm to 15mm MAY increase the pressure drop resulting in a smaller flow.

 

If all is well now - leave it as is. If you need a little more flow upsize some / all the 15mm to 22mm. I would be inclined to leave it all alone if it works OK.

 

Brit15

Thanks Apollo.

 

Unfortunately, I don't have the option of leaving it as it is because I am about to convert the loft.  The 22mm pipe runs diagonally across and about 150mm above several ceiling joists which means it will be in the way of the new floor joists and a steel beam.  I suspect I am just going to have to change it and see what the impact is and if the bathroom pressure is affected you will have pointed me towards a possible reason and solution.

[chris p bacon]

Rob, It sounds like the original 22mm delivery pipe from a tank feed to a bath tap, you can take out as much as you like and it won't affect the flow adversely, it could even improve it as there is less water for the water pressure to "push" out of the way. 

Combi boilers are now 22mm feed pipe in from a main (to give a larger water flow) and 15mm feed from boiler to sink/bath/shower,  In days gone past with a 15mm (old 1/2 inch) incoming main if more than one hot tap was opened then the flow would drop to a dribble, by having the incoming as a 22mm then the flow rate is improved to the boiler meaning more than one tap can be opened. without it affecting it too much.

 

On our last Combi installation we took the main from it's incoming position in the bungalow and fed the boiler first before taking the cold feed off, this meant the boiler is the last to be deprived of water/pressure even if there is a hosepipe running.

[jcm@gwr]

Firstly, the pipe would have been 22mm (3/4") because

it came from the storage tank and there wouldn't have

been enough pressure to feed the multiple outlets.

(a larger pipe will have more flow to compensate)

Also bath fillers have 3/4" tails, whereas the basin taps

and toilet are 1/2", so the pipe would have 15mm (1/2")

pipes 'teeing' off.

If your mains pressure is good, then reducing it to 15mm 

will have little effect, and is probably going to help to

balance it to the hot (the combi cannot supply hot at the

same rate, the hotter you have the water, the more the

combi has to slow it down to heat it, unless you have a

massive combi!)

If you can change the hot feed pipes from 22mm to 15mm,

you will benefit more by reducing the volume of cold water

you have to displace before you get the hot at the outlet.

(which will save gas!)

 

Edit: Dave beat me to it!

[Happy Hippo]

Fwiw, when I replaced the plumbing in our bathroom I removed the 22mm pipe from the bath and replaced it with a 15mm version.

 

The flow rate changed from good to abysmal!

 

Fortunately it was only a temporary job whilst we  carried out a complete refurbishment which also included a pump for the shower.

[chris p bacon]

Fwiw, when I replaced the plumbing in our bathroom I removed the 22mm pipe from the bath and replaced it with a 15mm version.

 

The flow rate changed from good to abysmal!

 

Fortunately it was only a temporary job whilst we  carried out a complete refurbishment which also included a pump for the shower.

If you installed a pump then it was because you were on a gravity feed so by reducing from 22mm to 15mm you effectively halved the water flow to the bath. 

 

You can't pump from a combi boiler.

[Enterprisingwestern]

 

 

You can't pump from a combi boiler.

 

Pedantically and technically you can, as there are pump systems to boost the incoming mains pressure.

As the dhw outlet from the combi will be 15mm, the delivery pipework only needs to be 15mm throughout, so removing the 22mm will have no adverse effect. The only problem i can foresee is that if the pipes are going up and over there may be a shorter run to the existing draw offs which will help with standing water not wasting heat and transfer time.

 

Mike.

[teaky]

Dave & Jeff - Thanks, that all makes sense.

 

Jeff - Just to pick up on your "Also bath fillers have 3/4" tails, whereas the basin taps and toilet are 1/2", so the pipe would have 15mm (1/2") pipes 'teeing' off."  One thing about which surprised me is that our original plumbing set up appears to be a mixture of direct and indirect feed.  My limited knowledge had me thinking that, typically, older systems are indirect feed, i.e. only the kitchen has potable water and other taps etc. are fed from the cold water cistern, and newer systems (with combi boilers) are direct feed with everything at mains pressure.  This had me scratching my head for a while struggling to figure out what the pipes in the loft did.  When I turned off the supply at the stop cock in the airing cupboard all the upstairs taps and toilets still worked.  It seems that our original set up had direct feed to cold taps and toilets, and indirect feed to the bath and shower.  When the combi boiler was installed the original cistern feed was connected to the bath and shower making them direct feed too (albeit with a convoluted pipe run).  On the bright side: my knowledge has increased a little and when I do make these pipe changes, the only things temporarily out of action will be the bath and shower.

[chris p bacon]

Pedantically and technically you can, as there are pump systems to boost the incoming mains pressure.

 

Mike.

Thats pumping the incoming feed to create a constant pressure, you cannot pump on the delivery side of the boiler. (I bet someone finds something obscure that say you can if there's a unicorn in your bath)

[teaky]

Pedantically and technically you can, as there are pump systems to boost the incoming mains pressure.

As the dhw outlet from the combi will be 15mm, the delivery pipework only needs to be 15mm throughout, so removing the 22mm will have no adverse effect. The only problem i can foresee is that if the pipes are going up and over there may be a shorter run to the existing draw offs which will help with standing water not wasting heat and transfer time.

 

Mike.

Thanks Mike.

 

I'm stuck with the pipe runs really.  If I want to change them I'd have get under floors and into walls and ceilings.  It would nice to have neat pipe runs and no redundant sections, but it is too much trouble so I'm going to live with the wasted heat and transfer times as they stand.  I may gain a little once the loft is done as part of the pipe runs will still be in the insulated sleeving but now be within an insulated floor space rather than an unheated loft.

[Enterprisingwestern]

Dave & Jeff - Thanks, that all makes sense.

 

Jeff - Just to pick up on your "Also bath fillers have 3/4" tails, whereas the basin taps and toilet are 1/2", so the pipe would have 15mm (1/2") pipes 'teeing' off."  One thing about which surprised me is that our original plumbing set up appears to be a mixture of direct and indirect feed.  My limited knowledge had me thinking that, typically, older systems are indirect feed, i.e. only the kitchen has potable water and other taps etc. are fed from the cold water cistern, and newer systems (with combi boilers) are direct feed with everything at mains pressure.  This had me scratching my head for a while struggling to figure out what the pipes in the loft did.  When I turned off the supply at the stop cock in the airing cupboard all the upstairs taps and toilets still worked.  It seems that our original set up had direct feed to cold taps and toilets, and indirect feed to the bath and shower.  When the combi boiler was installed the original cistern feed was connected to the bath and shower making them direct feed too (albeit with a convoluted pipe run).  On the bright side: my knowledge has increased a little and when I do make these pipe changes, the only things temporarily out of action will be the bath and shower.

 

You've about got your head round it, the excess pipework needs to be trimmed if at all practically possible.

 

Mike.

[Enterprisingwestern]

Thats pumping the incoming feed to create a constant pressure, you cannot pump on the delivery side of the boiler. (I bet someone finds something obscure that say you can if there's a unicorn in your bath)

 

Shows how far behind the regulations you are, it's a dodo in the bath now.

 

Mike.

[Colin_McLeod]

For a job/question like this I would seek professional advice from a qualified plumber whom you can let inspect the system. Just as one would for a major electrical or structural issue.

 

Best wishes with the overall project.

[chris p bacon]

For a job/question like this I would seek professional advice from a qualified plumber whom you can let inspect the system. Just as one would for a major electrical or structural issue.

 

Best wishes with the overall project.

Rarer than a Unicorn....Dodo in a bath.

 

The plumber I've worked with has said he's going to retire as he's 74 next year and it's been a huge headache to find another that has any idea what he's doing. It seems a a couple of weeks at the local college is enough to say "Qualified".....Found someone eventually.

[teaky]

For a job/question like this I would seek professional advice from a qualified plumber whom you can let inspect the system. Just as one would for a major electrical or structural issue.

 

Best wishes with the overall project.

Normally I'd agree with you Colin but on this occasion all I am going to end up doing is swapping about 3m of 22mm pipe for 15mm and altering the overall shape so that things are at right angles rather than chopping across the joists.  Now that I have figured out that it is only the bath and shower that are affected I should be able to make these changes well in advance of the builders coming in and, therefore, only call in a professional if the water pressure is affected negatively.  There's nothing safety related here and all the amended pipework will be visible in the short term so I'm comfortable with making the alterations.

[34theletterbetweenB&D]

...our original plumbing set up appears to be a mixture of direct and indirect feed.  My limited knowledge had me thinking that, typically, older systems are indirect feed, i.e. only the kitchen has potable water and other taps etc. are fed from the cold water cistern, and newer systems (with combi boilers) are direct feed with everything at mains pressure.  This had me scratching my head for a while struggling to figure out what the pipes in the loft did.  When I turned off the supply at the stop cock in the airing cupboard all the upstairs taps and toilets still worked.  It seems that our original set up had direct feed to cold taps and toilets, and indirect feed to the bath and shower...

 My observations based on my own and friends and relatives homes over the years is that the direct feed to kitchen tap, all other water in the house drawn from a header tank (cold water cistern) usually in the loft or attic would be typical of pre WWII build. Post WWII the direct feed to all cold taps and toilets, indirect feed from header tank to bath arrangement you have deduced became usual. And then at some date with the introduction of combi boilers and the like, houses may be built or modified to all take off points at mains pressure, and there is no cold water header tank. But that's just amateur observation, I am sure a time served plumber could tell more.

[Arthur]

Rarer than a Unicorn....Dodo in a bath.

 

The plumber I've worked with has said he's going to retire as he's 74 next year and it's been a huge headache to find another that has any idea what he's doing. It seems a a couple of weeks at the local college is enough to say "Qualified".....Found someone eventually.

Agree there. We've a bathroom with ceramic disc, quarter turn 'waterfall' taps built into the bath itself. One of the taps developed a strange problem, dripped when turned off yet had almost no flow when turned on. Replacements were not available. Two different plumbers both said can't be fixed you'll need to install new non matching taps. No examination of the taps, just can't be done. Installing taps as suggested would have looked awful.

 

Bit the bullet, took the tap off, had a look, and fixed it myself.

[Free At Last]

While we are on plumbing, where can I get a syphonic toilet from? Had one in my last house, it left nothing behind.

[chris p bacon]

While we are on plumbing, where can I get a syphonic toilet from? Had one in my last house, it left nothing behind.

A Museum.....

 

I don't think they meet current regs as they use a lot of water and I can't remember the last time I saw one for sale let alone in a house. I did say to one customer a few years ago that if the contents didn't go with the first flush it was the diet that needed changing not the WC.

[chris p bacon]

 My observations based on my own and friends and relatives homes over the years is that the direct feed to kitchen tap, all other water in the house drawn from a header tank (cold water cistern) usually in the loft or attic would be typical of pre WWII build. Post WWII the direct feed to all cold taps and toilets, indirect feed from header tank to bath arrangement you have deduced became usual. And then at some date with the introduction of combi boilers and the like, houses may be built or modified to all take off points at mains pressure, and there is no cold water header tank. But that's just amateur observation, I am sure a time served plumber could tell more.

It really depended on the plumber fitting the house out.

 

I have always prefered all cold taps to be direct feed so that there isn't a problem if someone should drink from one but I know of some plumbers who made the cold tap in the kitchen the only one. I do remember when I questioned why, the answer was it was just easier.

[34theletterbetweenB&D]

.... I did say to one customer a few years ago that if the contents didn't go with the first flush it was the diet that needed changing not the WC.

 Good theory, but I challenge. We have in our family a nameless someone with a circa 3 inch diameter exhaust. Instead of logs, the output is depth charges roughly the size and shape of a Nestle Carnation 397g condensed milk tin.  These are practically custom designed plugs for the two close coupled WC's in the house, he has to be reminded when visiting with us to only use the 1950s downstairs WC with its capacious four inch outlet.

[chris p bacon]

 Good theory, but I challenge. We have in our family a nameless someone with a circa 3 inch diameter exhaust. Instead of logs, the output is depth charges roughly the size and shape of a Nestle Carnation 397g condensed milk tin.  These are practically custom designed plugs for the two close coupled WC's in the house, he has to be reminded when visiting with us to only use the 1950s downstairs WC with its capacious four inch outlet.

Does my brother come and stay with you?