Selecting cortrect radiator tails 20mm & 25mm connectors

Ant555

Can anyone assist in selecting some radiator tails please.

Existing 800mm wide radiator removed and I am looking at putting a 700mm wide one in its place.

A google search reveals that I should be able to get extendable tail pipes to suit but what I don't know is how I select the correct size at the existing pipe - one is 20mm and one is 25mm (1 inch?)

I have drawn a pic - link here
https://www.dropbox.com/s/w06kzrghqjvb3zq/20191124_183435.jpg?dl=0

Can anyone with plumbing experience please point me in the right direction.
Thanks

neilmcl

Why put in a 700mm rad, what's wrong with an 800mm?

Ant555

neilmcl wrote: »

Why put in a 700mm rad, what's wrong with an 800mm?

A valid question but I bought a brand new 800mm rad and there is barely enough room for me to place the rad between the pipes let alone add connectors and tails to it.
The one I got from screwfix measures 812mm between the pipe outlets at the bottom of the rad - the rad panel itself is 800mm wide but the connector bits protrude beyond - which I thought was weird but I have the luxury of laying both rads on the floor and measuring.
Old one 796mm distance between connectors, new one 812 and its all a bit tight. New rad is pretty much butted up against the pipes before I add any connectors or couplers - 700w x 600h rad is more than enough watt/btu for the room so I thought that would be the easy options here.

Im thinking the 25 year old radiator I took off the wall (showing signs of rust) is an old or weird size.

king132

I'm no plumber but wouldn't you be able to use a 20mm piece of copper pipe, attach it to the 20mm trv with the fittings in the box and then use a 25mm to 20mm compression reducing coupler (brass type)on the other end?!

ianto11

From your drawing is it the external thread your measuring, so although the TRV has a 20mm diameter thread and the lockshield has a 25mm diameter thread, are they not just connected to standard 15mm copper into the rad ?

ianto11

20mm thread is 1/2"BSP nut....25mm is 3/4" BSP nut

ianto11

Link (table halfway down page )

neilmcl

Ant555 wrote: »

A valid question but I bought a brand new 800mm rad and there is barely enough room for me to place the rad between the pipes let alone add connectors and tails to it.
The one I got from screwfix measures 812mm between the pipe outlets at the bottom of the rad - the rad panel itself is 800mm wide but the connector bits protrude beyond - which I thought was weird but I have the luxury of laying both rads on the floor and measuring.
Old one 796mm distance between connectors, new one 812 and its all a bit tight. New rad is pretty much butted up against the pipes before I add any connectors or couplers - 700w x 600h rad is more than enough watt/btu for the room so I thought that would be the easy options here.

Im thinking the 25 year old radiator I took off the wall (showing signs of rust) is an old or weird size.

Did you remove any bungs in the connector points where the tails will go before measuring, I would be very surprised if these holes protrude beyond the panel itself. What make of rad? A 800mm radiator plus tails is going to be around 820mm wide.

Ant555

ianto11 wrote: »

20mm thread is 1/2"BSP nut....25mm is 3/4" BSP nut

I have seen those acronyms quoted but was equating the sizes incorrectly

25mm I was thinking is 1"
20mm I was thinking is 3/4"

Did you remove any bungs in the connector points where the tails will go before measuring, I would be very surprised if these holes protrude beyond the panel itself. What make of rad? A 800mm radiator plus tails is going to be around 820mm wide.

Yes, bungs removed. I wonder if its a quality control issue as those bits definitely protrude 6mm beyond the radiator at each side which I too was surprised about and have checked, measured, glasses on/glasses off etc. I could tell immediately that it was far wider than the old one when I held the bare rad up to the pipes and it pretty much touched them at both sides.
Its a Kudox rad from Screwfix.

Anyway, thanks to everyone for the assistance - I'll speak to a plumber (which is what I was hoping to avoid!)