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

[chapeau]

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

Cheers Chris.

Oh that's a low blow....

But you cannot argue with my content. As long as he finds a skilled tradesman who can measure up and pull bends in copper pipe then solder a joint, and not a bodger who can unroll plastic and press inserts on the end - then he will be fine.

Flow is dependant on cross sectional area of the bore, not external diameter of the pipe.

Simples...

 

[doitall]

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

Combi depends on you hot water needs, 10ltrs/min average and they are great.

Changed my 40 plus year old Servowarm for an Intergas HRE 2 year almost to the day. Great boiler with non of the usual suspect parts.

And 22mm pipe will be a complete waste of time unless you can increase the pressure, and an even bigger waste if you go the combi road.

 

[chapeau]

Nope, you are wrong, with a gravity system increasing the bore has a definite effect on flow and the pressure (head) stays the same.

Baths in these systems have their hot water taps plumbed in 22mm for a reason.

This is really really simple stuff.

 

[Agile]

Thanks lads,

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

There is nothing so very wrong with a gravity HW system:-

Store of water in case mains fails.

Works without electricity or gas.

BUT

Pressure is poor upstairs.

Takes up space in the loft.

Can leak and bring down ceilings.

Needs 22 mm pipes.

 

[Agile]

Thanks lads,

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

Now have you looked up the efficiency of your Potty King?

And then calculated the cost of the gas you are wasting keeping it?

If your house and gas bill is higher like £1500 pa then you could easily be wasting £400-£500 compared with the cost of running a nice condensing boiler!

Tony

 

[ChrisR]

This is really really simple stuff.

So simple you'll be able to tell us what all the other factors other than pipe diameter are. Start with the internal friction parameters appropriate for polybutylene and then pex and do the sums for those perhaps?

While you're at it you'll be able to work out what pipe thickness I already put in when I worked out the head drops above.

We'll wait to be astonished what difference you get, for this 3 metres of pipe.

 

[chapeau]

er, your figures prove my point.

The internal friction of the pipes is negligible compared to the decrease in cross sectional area due to the increased wall thickness of plastic pipes.

 

[ChrisR]

1)I didn't give you figures on that.

But NO it's not negligible - you do the sums.

2) you don't have a "point". The guy has only a 10cm head loss with 15mm pipe.

 

[chapeau]

And it's less with 22mm, as you demonstrated. Which is my point.

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

The different in surface friction in a plastic/copper pipe at 5l per min is trivial. It only shows at higher flow rates. Completely irrelevant at the flow rates in a gravity system.

BUT

The resistance to flow in a pipe is inversely proportional to the radius ^^ 4 !

That's the fourth power !!!!! Small changes in bore have dramatic effects on flow rates.

So, are you somebody who thinks it's OK to put 15mm plastic pipe and fittings on the hot water side of a gravity system?

 

[ChrisR]

And it's less with 22mm, as you demonstrated. Which is my point.

You need to learn what "significant" means.
10cm head difference on a head of around 2.5m makes no significant difference.
You don't have a point.

^^ 4 ! ... the fourth power !!!!!

Oh no it's not.
Back to skule for you.
Now run along.

 

[chapeau]

Excuse mistakes on phone...

Equation is

http://upload.wikimedia.org/math/d/7/f/d7fc954111a08e3140b5005f6014bd32.png

where change in pressure in inversely proportional to radius to power of four.

Do you use plastic pipe in hot water gravity systems?

 

[ChrisR]

Look at the title of the thread.
The answer's still "no".

And you've got the wrong equation.
It's very basic plumbing knowledge.

ANY pipe in gravity systems can be fine, or not, it depends.
You have to see what's significant. Perhaps you'd like to look that up on Wikipedia too.

 

[chapeau]

So you should point me to the correct one.

What's the equation for drop in pressure for a fluid in a pipe?

 

[chapeau]

Ok, back on computer.

That equation image above didn't come out well but it shows the change of pressure for fluid flowing in a pipe is inversely proportional to the radius ^^ 4.

But let's stick to tables as you might understand them more.

http://www.copperinfo.co.uk/plumbin...-copper-tubes-in-domestic-heating-systems.pdf

Looking at the figures you gave above Chris, which were taken from a table (and you misread the table by the way), they also show that the loss in pressure (m head per m run) are inversely proportional to ( radius of bore ) ^^ 4. Stick some numbers in and you will see that's how it works.

As for what does 'significant' mean? Well to me, it is a statistical concept relating to confidence intervals and whether something happens due to chance alone. Generally measured using p, significant is p < 0.05.

In the case of plumbing, it means does the punter think it's better.

And using fatter pipes without those nasty plastic inserts will make the punter a happier man, even if you like to blame the tap.....

 

[doitall]

The only way you'll make the punter a happy man in this case is too change the taps or increase the pressure.

And fatter pipes will do neither.