28mm pipe boiler flow/return

[lonspwi]

Hello,
I have a question -
The flow and return pipes from boiler are 28mm and they are reduced down to 22mm when they reach the divertor valve and pump on the first floor.

Now, are there any reasons why the 28mm pipe from the boiler cant be reduced down to 22mm as soon as they leave the boiler ?
Or is there a certain length the 28mm pipes have to be continued from the boiler, before they can be reduced.

Thanks in advance

 

[kevplumb]

sound's as if an old gravity system has been converted to fully pumped

 

[Bahco]

Changing down to 22 mm would not noticeably affect the flow as the water is being pumped around your system.

Why would you wish to change from 28 to 22?.

I can't see how you will benefit unless you are bored and want something to do.

 

[ChrisR]

WRONG ANSWERS! IT DEPENDS HOW BIG THE BOILER IS!
EG A Suprima 120 is likely to lock itself out on overheat fairly frequently if the pipes are too small.

You can and should do the simple sums to determine what you need

 

[kevplumb]

yeah so when it get's the flow restriction of a 22 mm three port valve all is rosy

 

[ChrisR]

I've got lots of 28mm 3 ports. I might even sell you one at a quid below RRP
And before someone says the resistance of a 3 port is more than a 2 port, look it it up. With the make I saw last, it wasn't.

And "get's" shouldn't have an apostrophe.

 

[kevplumb]

scuse me for only being a lowly working man



or not at the moment

 

[ChrisR]

Yer, can we assume you're "resting"? I'm just OFF to work..

 

[kevplumb]

you assume what you like marra
i'm wrapping myself round 2 gall of grog

 

[doitall]

Yer, can we assume you're "resting"? I'm just OFF to work..

I had to start at 7:30 AM

 

[kevplumb]

grabbing git

 

[lonspwi]

Thanks for all the replies.
It certainly does look like a gravity feed conversion to fully pumped, the boiler is quite old, and there are a few hacked out 28mm pipes lying under the floorboards on the first floor.
Considering the pipes are 28mm up to the diverter valve/pump and then 22mm from then on, i.e feeding the rest of the rads and the heating coil in the cylinder, is it feasable to replace the 28mm pipes with 22m up to, say, a metre from the boiler ? The reason I want to do this ? - I am moving the cylinder and want to tidy the pipes at the same time.

 

[ChrisR]

IT DEPENDS HOW BIG THE BOILER IS!


Is that easier to read? Find a figure in Btu/Hr or kW.

 

[lonspwi]

I can understand your argument if the complete circuit was 28mm, but surely when the 28mm pipe is reduced at the divertor/pump/cylinder as it is already, the flow rate is not going to be any greater if the 28mm pipes are 4 metres or 1 metre in length.
Even if I instal a 28mm divertor, the flow is again going to be restricted once it reaches the cylinder and the CH pipework on the first floor.

*Unless* the divertor is at mid position, I suppose.

BTW the boiler is rated at 80000btu

 

[doitall]

It depends how big the boilers is, this also applies to the size of the system and the two go hand in hand.

At 80000 btus you have a larger than average 2 bedroom semi.

Back to the boiler, for it to opperate with the minimum of circulation problems the main flow and return would be at least 28mm up to and including the divertor valve, 22mm would then be run to the cylinder when on a pumped system and a minimum, again this depends on the installation 22mm for the heating, but more often than not 28mm to at least the split between floors.

Unfortunately good practice and design is getting left in the closet as more and more so called plumbers chuck plastic pipe in by the van load.

You can only be adviced as to the importance of ChrisR comments.