On 21/05/2016 08:57, Tim Lamb wrote:
In message , polygonum
writes
On 21/05/2016 07:41, Andy Burns wrote:
Tim Lamb wrote:

Question 2 concerns Posi-joists.
Heating designer is opposed because you can't cut a slot through the
top
section to return the underfloor heating pipes.

With all them 'oles in the metal web, why would you even want to cut
slots?


So glad you asked that, Andy. Read the question last night and
scratched my head thinking I must be missing something. Still can't
see what...

Sorry! Inadequate description. Heating engineer is used to dealing with
conventional timber joists and his fitters expect to be able to cut a
15mm depth slot in the joist top to cross into the next joist/pair run.
They nail on a *p* clip to retain the pipe.

Because this is a chalet bungalow where the internal walls upstairs are
some distance in from the outer walls (joist supports) I am resisting
having slots cut of any depth.

My thinking is to take the pipe under the wall and return through or
over the Posi- joist. Hence lots of places where a length of pipe is
able to trap air.

For a unvented (i.e. pressurised) primary heating circuit, air traps are
not really much of an issue. It may make it slight harder to drain down
completely, but filling is usually straight forward, even if you do have
to do a second round of bleeding and topping up once the system is running.


--
Cheers,

John.

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