Gravity fed sink pressure scenario

[PASUK]

Hi
Doing up my bathroom and wanted to ask [more] questions hoping for some help...
On a gravity fed system at home and the current bathroom sink hot and cold feed is great (no pumps to the sink), no complaints at all about the pressure or hot water.

The current bathroom sink happens to be the room just under the water tank and the hot water cylinder is in a cupboard in the same room. Per my very simple diagram:

I am installing an additional bathroom on the same floor, but the other side of the house.
It is very difficult to pull up all the floors to get pipes via under the floorboards so the only practical way is up into the loft and back down a stud wall per my next diagram - (truly this is my best attempt at drawing my plumbing!)

My first concern and request for advice is whether the hot water might struggle without a pump to go up to the loft and over a ~10 mtr horizontal stretch and still maintain decent pressure like we have at the moment in the main(first) bathroom.

Of course this scenario isn't just a sink, a toilet and shower will be installed...

I was told to consider having a pump in the loft for the shower only.
I would prefer to situate the pump nearer the hot water cylinder as I'd prefer the noise to be that end of the house and for maintenance purposes it's easier to get to, but not sure about having the sink and toilet on the same pipe that will push highly pressurized water from the pump. So ultimately I am concerned about too much and too little pressure in either scenario.

Any advice on best practice or alternative options would be appreciated.

Thank you

 

[terryplumb]

The hot supply for shower should come directly from the cylinder ,via a suitable flange ,and dedicated to the shower only. The cold supply should also be a dedicated supply to the shower from the loft tank. Both via the pump.
The cold supply to WC can be fed from the cold mains ,as can the cold to the basin if seperate taps are used (as opposed to a mixer ,which would be better fed from the loft tank)

 

[PASUK]

Thank you v much @terryplumb
The sink is indeed a mixer so I think it is best to run 4 15mm pipes to that new bathroom.
One pair via water pump for the shower.
One pair (cold from loft water tank and hot from the hot water cylinder) for the sink.
Do you think if the current bathoom sink pressure feels more than enough that using gravity fed for the sink in this way will still be ok pressure or going up and 10mtrs over create a large loss of pressure?

 

[terryplumb]

The pressure would be the same ,however, the flow rate would be less. That would be due to the restrictions in the supply pipework , particularly the hot, more bends = more resistance to flow. Small bore flexible tap connector hoses on mixer taps being the greatest restriction. Is your existing bathroom tap a mixer ?

 

[PASUK]

Hi - yes existing bathroom taps are a mixer and pressure is v good.

 

[terryplumb]

Then your new one should be ok ,albeit slightly less flow.

 

[PASUK]

Many thanks!

 

[Harry Bloomfield]

The up and back down layout will also be inclined to cause airlocks, in the hot supply. Always better to go down first, along, then up to minimise them.

 

[PASUK]

The up and back down layout will also be inclined to cause airlocks, in the hot supply. Always better to go down first, along, then up to minimise them.

This was actually a problems before, if the system was every drained, getting back up and flowing was almost impossible. Any way of fixing this? a component that would allow the air out on refill perhaps?

 

[Harry Bloomfield]

This was actually a problems before, if the system was every drained, getting back up and flowing was almost impossible. Any way of fixing this? a component that would allow the air out on refill perhaps?

A question for the plumbers - could an automatic bleed valve be fitted, be worth fitting?

 

[Madrab]

Under normal conditions, with a gravity system like that you would fit manual bleed valves at the highest points in the system. On that I would fit 2, one at the top bend as it rises into the attic and one at the other bend where it drops. Don't fit AAV's, over time they're almost 100% guaranteed to leak.

How large is the cold water storage cistern (CWSC)

Given all this work you are doing and expense, have you considered converting to a mains cold and unvented HW, rather than pumping? Mains cold supply and pressure not withstanding of course.

 

[PASUK]

Thanks again, manual sounds like a good option as whenever we have had the issue has only been when we drain and refill the system, but never once it's all running so doing a manual bleed on refill (which is rare occurrence anyway) is very ok!

How large is the cold water storage cistern (CWSC)

I should go and measure it as I don't know off hand, I do know it seems huge (not helpful I know!) and take up a load of space but maybe the insulation is hiding a small tank! I'll get a measurement later. Curious as to the question, might it be a concern if the tank is small and I'm using pumps etc that I may drain the tank faster than it can refill?

Given all this work you are doing and expense, have you considered converting to a mains cold and unvented HW, rather than pumping? Mains cold supply and pressure not withstanding of course.

I had two quotes to shift over from locally recommended pros and the cost was really high and of course not a job I can tackle myself. But it is a good point and did really want to consider it. It's also so hard to find availability of a good professional these days!

 

[Madrab]

I may drain the tank faster than it can refill?

Yes, you are adding demand without understanding capacity, never a good starting point. Check the size of the HW cylinder too.

the cost was really high

It can be, but over the longer term ... that's another consideration ... that and it vastly simplifies your HW and CW systems.

Cost is a factor of course but hugely expensive? What were the quotes and what were they recommending? resource availability is another point of course.

 

[MeldrewsMate]

Have you considered raising the height of your present cold water tank?
You have been given good advice re: locating the pump low in the airing cupboard - this will avoid air bubbles as far as possible and lead to longer pump life.
I would also add that I advise against using pumped water to the WC - the pump will start and stop several times on each nightime flush, which will be irritating. Better advice (already supplied) is to connect the toilet supply to the cold mains feed already in the loft.

If you're going to take gravity hot water across the loft, tee into the hot supply as low as possible before rising to the loft, again to avoid airlocks. It can be tempting to tee into the hot vent pipe already in the loft, but that is almost guaranteed to create HW airlocks.

Manual air vents - definitely, but keep them short and covered in insulation.

 

[PASUK]

Yes, you are adding demand without understanding capacity, never a good starting point. Check the size of the HW cylinder too.
It can be, but over the longer term ... that's another consideration ... that and it vastly simplifies your HW and CW systems.

HW cylinder is about 250ltrs (label in tank is unreadable but I did a simple diameter and height measurement excluding the insulation)
Cold water tank is 227ltr (found the label on this one!)
So what I do know is that the property previously had a extra bathroom when we moved in but it was falling apart and we stopped using it. So I'm assuming I'll be ok because I am reinstating the same overall demand the house had when we first got it. Although who's to say the water tanks were fit for that purpose in the first place. Do the numbers above look ok?
We do fire up the boiler for the hot water twice a day which serves the household ok.

Cost is a factor of course but hugely expensive? What were the quotes and what were they recommending? resource availability is another point of course.

Got two quotes, both came in about £3k parts and labour to replace the cylinder with an unvented one and associated pipe work. It does not include upgrading the water feed from the street to the property which is the old smaller standard (sorry don't know the name). They both said I *might* get away without upgrading it but ideally it would be upgraded which would need the drive to be dug up for the trench to replace it and I'd need to organise that myself. Seemed like a lot more cost and hassle - but I could be wrong!

Have you considered raising the height of your present cold water tank?
You have been given good advice re: locating the pump low in the airing cupboard - this will avoid air bubbles as far as possible and lead to longer pump life.
I would also add that I advise against using pumped water to the WC - the pump will start and stop several times on each nightime flush, which will be irritating. Better advice (already supplied) is to connect the toilet supply to the cold mains feed already in the loft.
If you're going to take gravity hot water across the loft, tee into the hot supply as low as possible before rising to the loft, again to avoid airlocks. It can be tempting to tee into the hot vent pipe already in the loft, but that is almost guaranteed to create HW airlocks.
Manual air vents - definitely, but keep them short and covered in insulation.

Thanks for that.

So after doing some pipe work in the bathroom and taking them up into the loft I discovered two 22mm pipes which presumably served the bathroom. I haven't yet been able to trace if it takes the HW feed from low in the cupboard vs the vent pipe. I will need to investigate this tomorrow. If it is coming from lower in the airing cupboard then it is so tempting to use this to supply the bathroom! However this brings back the potential issue of using this pipe to then tee off it (22mm in and reduce to 2x 15mm) and the pipes going to the shower having a pump above the bathroom in the loft. Interestingly the guys that gave the quotes were suggesting to locate the pump in the loft so wondering if I could somehow try to test this. + of course install manual air vents. Or is this all a really bad idea!?