Changing bath from 15mm to 22mm

[EAST61]

I've got the ceilings down downstairs at the moment on a house I'm renovating.

Bath taps take a 3/4" threaded connection and I can see they currently have 15mm pipe plumbed in. The 15mm is about 1 metre in length teed off some 22mm.

It would be trivial for me to change the 15mm to 22mm direct to the taps.

Mains flow rate is 20lpm at 2 bar static. 22mm into/out unvented cylinder.

I should do it, right? The bath will fill up a lot quicker?

 

[ianmcd]

All depends on what supplies your water ? is it a Combi Boiler ? an unvented Cylinder ? a stored cylinder ? static pressure means absolutely nothing to anyone other than your water supplier

 

[EAST61]

I said it right there Ian!

 

[ianmcd]

so did I , static pressure means absolutely nothing , you have 20 L/Min flow rate so what do you think you would achieve by increasing the diameter for the short length to 22mm ?

 

[EAST61]

I don't know that's why I'm asking you.

I said in my first post I have an unvented cylinder with 22mm pipe you doughnut.

 

[oilboffin]

Now now don't be rude to someone who's trying to help you people come on here asking for help and if we make a mistake we get abused how dare you give Ian some respect he's been in the trade for years forgot more than you'll ever know DOUGHNUT

 

[EAST61]

How dare I call someone a doughnut? Do you struggle to get through a day without being fake offended?

Don't be so sensitive, it's all light hearted. I'm sure Ian will recover from being called a doughnut.

 

[EAST61]

so did I , static pressure means absolutely nothing , you have 20 L/Min flow rate so what do you think you would achieve by increasing the diameter for the short length to 22mm ?

Out of interest, would the answer change if:

- the current 15mm run was longer, say 10 metres

Or

- it was to serve a shower not a bath

Thanks for your help

 

[oilboffin]

Technically the flow would increase slightly but as the feed is from an unvented cylinder it really
wouldn't be worth doing but there will be people who will disagree.Bob

 

[EAST61]

Is it fair to say the with an unvented cylinder the bigger the pipes the better? or are there some situations where small diameter pipe is preferable?

For example I can see that my bath takes 3/4" but my shower takes 1/2". Do showers provide a better experience with small pipe?

 

[copea]

No, but with a smaller bore you have less cold standing water to run off before you get the hot to the outlet.

 

[EAST61]

Understood copea. But would the shower be "better" I.e. More powerful with 22mm or 15mm pipe?

 

[copea]

It'd be the same on both. The shower is the bottleneck.

 

[EAST61]

Thanks!

And if I wanted to Install a new shower 10 metres away from my unvented cylinder, the shower performance would be the same on 10m of 22mm versus 10m of 15mm? Wouldn't the resistance in the 15mm be higher causing a poorer shower?

Sorry for all the questions!

 

[copea]

Yes and yes.
But not enough to make any noticeable difference.