Hello,

I was browsing through some old posts and they said that 15mm pipe was
suitable for carrying up to 6kW according to one post and 9kW
according to another.

I'm a bit worried! It's very cold upstairs. We moved in last year and
the first thing we did was to insulate the loft. That hasn't been
enough, so I was going to change some radiators to bigger ones.

The thing is that the boiler has 22mm pipe come out of the boiler and
upstairs but on the landing this is reduced to 15mm which tees, with
one 15mm run going to the back rooms and one 15mm run going to the
front rooms. I am sure there must be more than 6kW of radiator
connected to that!

Is this why it's so cold? Will upgrading the rads. have no effect if
it is that the pipe cannot carry that capacity?

I'm not sure if it would be easy to change the pipe work without
ripping up the floor in each room. I would use plastic pipe to weave
through the joists. At the moment they've taken a big chunk out the
top of the joist to fit the two 15mm pipes through. That would be too
small to fit two 22mm pipes in, so I guess I'd be best to drill two
22mm holes in the middle of the joists. How far away from the existing
notch would I need to be to make sure I do not weaken the joist?

I also noticed that the gravity fed HW goes from the boiler in 28mm
pipe but is reduced in the airing cupboard to 22mm.

In both these cases, doesn't it defeat the object of using big pipe if
you then reduce it down later 22 to 15, or 28 to 22?

Thanks.