The Verdict ! Will the 22mm pipe increase the hot taps flow?

[masona]

Got water cylinder and the hot feed draw off is in 22mm but the shower basin and the kitchen hot supply flow rate is poor and it's in 15mm copper pipe approximately 3-4m run, will the 22mm all the way increase the flow at the from the water cylinder to the hot taps The bathroom hot basin tap is okay.

 

[Armo74]

Yes. Ideally on a gravity hot water system you should run as far as you can in 22mm with as little amount of joints as possible nice sweeping bends are preferred. A 90 degree elbow can add the equivalent resistance as an extra half a metre length of pipe. 22mm also holds about twice as much volume of water. Choosing the right taps will help aswell.

 

[doitall]

Yes and no.

If you had an open pipe you'd get more water out of the 22mm than the 15mm.

However if you have high pressure taps for example, the higher volume would not improve the flow, you will need an increase in pressure to do that.

 

[masona]

Choosing the right taps will help aswell.

However if you have high pressure taps for example, the higher volume would not improve the flow, you will need an increase in pressure to do that.

How do we know what taps to buy unless they do low pressure taps?

Is it written on the instruction?

I can run a temporary 22mm plastic pipe from my bathroom basin which is a good flow and run it over the floor to the kitchen tap to test the flow. Am'I being silly doing this?

 

[Armo74]

They will either be high or low pressure, Low pressure will usually be suitable for a minimum of 0.1 bar which is 1m head of water. Low pressure taps would be ok on high pressure systems. It will tell you on the box/instruction's.

 

[masona]

I'm assuming the high pressure taps are design for combi boilers?

 

[doitall]

Yes and unvented cylinders, or boosted where a pump is fitted.

 

[Agile]

Not really!

High pressure taps are cheaper to make and are fine for 98% of the world where hot water is derived from mains pressure .

In the UK we are pretty unique is having a few houses still supplied with gravity hot water!

Tony

 

[masona]

In the UK we are pretty unique is having a few houses still supplied with gravity hot water!

Tony

Is the gravity hot water slowly fading out in the UK?

If I go for a Combi boiler which most of my hot supply is in 22mm copper pipe, will that cause any problem with flow rate?

Is it also difficult to change the pipework from gravity to Combi set up?

 

[doitall]

15mm is ideal for a combi set-up provided the mains pressure can deliver, 22mm is not good for a combi boiler.

 

[ChrisR]

Is the gravity hot water slowly fading out in the UK?

Ever so gradually, but some properties will have it forever. If you've got a straightforward oldfashioned tap and a floor or more of head, then the flow is ok, so most people are happy. Fancy taps are a pain, even a combined single lever one designed for "low pressure" won't have great flow from a tank on the floor of the loft above, whether it's fed by 15 or 22. It's the tap that matters. "Designed for 0.1m head" means little if they don't quote a flow rate.

That 3-4m lengh of pipe is not likely to make a difference you can see, though you may be able to measure it, would be my guess, though I don't know the nubers you'd have.

I thought I'd get my calculator out as you're an old timer here masona ...
assuming a lowish flow rate of 5 litres per minute, you'd have a head loss per metre of ~ 2.5cm with 15mm, and 0.4cm with 22mm.
3m, 3 elbows, makes maybe 10cm head difference
Not enough to show much, if your pipe head's say 2.5 metres.

A better tap would mean more flow so the pipe makes more difference, but with better flow, you'd care less!

By the way some tap flexible connectors are quite restrictive, but again not usually too significant compared with the tap itself.


22mm on a combi means it takes longer for the hot to arrive, and you waste more heat when you turn it off, though often the house gets it.

 

[masona]

Thanks lads,

22mm on a combi means it takes longer for the hot to arrive, and you waste more heat when you turn it off, though often the house gets it.

All the plumbers I'm hearing are quoting the Combi are the way to go but I would have to change a lot of pipe work to do this, I was never keen on Combi boilers in the early days but I believe they are getting better(?) My Potterton Kingfisher boiler is now over 30 years old and so reliable so far and I find it hard to go the Combi route

 

[Armo74]

If it's not broken why fix it?

 

[chapeau]

Got water cylinder and the hot feed draw off is in 22mm but the shower basin and the kitchen hot supply flow rate is poor and it's in 15mm copper pipe approximately 3-4m run, will the 22mm all the way increase the flow at the from the water cylinder to the hot taps The bathroom hot basin tap is okay.

22mm COPPER will be better. Don't let any bodger put plastic in as the bore is significantly smaller due to the extra thickness of the plastic wall. We had some monkey put 15mm plastic on the hot part of our gravity system and the bloody water just trickled out. I had to replace it all which was hassle.

The cross sectional area of the bore is what counts and it's really significantly reduced in plastic. They talk about the external diameter and they just don't geddit. You (should) also put inserts into the plastic pipe at joints and they close it down even more...

 

[misterdubya]

Got water cylinder and the hot feed draw off is in 22mm but the shower basin and the kitchen hot supply flow rate is poor and it's in 15mm copper pipe approximately 3-4m run, will the 22mm all the way increase the flow at the from the water cylinder to the hot taps The bathroom hot basin tap is okay.

22mm COPPER will be better. Don't let any bodger put plastic in as the bore is significantly smaller due to the extra thickness of the plastic wall. We had some monkey put 15mm plastic on the hot part of our gravity system and the bloody water just trickled out. I had to replace it all which was hassle.

The cross sectional area of the bore is what counts and it's really significantly reduced in plastic. They talk about the external diameter and they just don't geddit. You (should) also put inserts into the plastic pipe at joints and they close it down even more...

Spoken like a true Joe...... erm pro.....

Cheers Chris.