Limit on heat from 15mm pipes?

[Martin Pentreath]

Hi,

As part of my efforts to get the living room warm enough to actually be habitable over the winter I've done a quick heat-loss calculation and realised that the "professional" who did some work on the heating system a few years back undersized the rads so that the room only has around 60% of the heat going into it that it should have. That could explain a few things.

Anyway, a nice new rad turned up today to go under one of the windows to beef things up. The easiest way to plumb this in is to T off from the flow and return to a nearby rad. If I do this there will be a total of around 8.5kw all coming off one spur of 15mm pipes. Can 15mm pipes carry this much heat, I'm wondering? I could go back and T off from the main 22mm pipes, but frankly that will be a pain in the arse and require a lot of floorboard-lifting and joist-notching (not to mention extortionate copper-tube-buying) and I really don't want to.

Cheers!

Martin

[grimly4]

Rough rule of thumb:

28mm - 24kW 22mm - 12kW 15mm - 6kW

[Nutkey]

Plastic won't be any cheaper, but you wouldn't have to notch...

[Doctor Drivel]

Not quite so...

Condensing boilers with a 20C temp differential require smaller pipes, making them more economic to fit.

At 11C temp diff:

15mm - 6.0 kW 22mm - 13.4 kW 28mm - 22.5 kW

At 20C temp diff:

15mm - 9 kW 22mm - 24 kW (81,888 BTU/hr) 28mm - 70 kW

[Roger Mills]

The rule of thumb puts an arbitrary 6kW limit of 15mm pipes. AIUI, this is based on limiting the flow velocity to a level where it won't create noise. If you don't mind the noise, you can wind the pump up and increase the velocity. Or, as others have said, if you can accept a larger temperature drop across your radiators, you can extract more heat at a lower flow rate, and go beyond the 6kW limit.

[Nutkey]

Drill a hole in the centre of the joist.

[Jonathan]

Why can't you do that for copper pies?

Jonathan

[Phil]

You could ... if you could then get the pipe in! (sometimes possible)

[NT]

all you need to achieve that is an overrated rad.

NT

[82045]

15mm sometimes, 22 or 28 never.

[John Rumm]

You could, but you might have to carry on through the outside wall to give you a straight path to run the pipe in!

[dennis]

That maths doesn't add up.

[Doctor Drivel]

Dennis, please do not think.

[Doctor Drivel]

...and a condensing boiler.

[dennis]

So you don't see what's wrong then.

[ARWadsworth]

If I was a child in a playground I would now be shouting "fight fight fight"

FIGHT, FIGHT, FIGHT

[Roger Mills]

You probably could if you made sure that the holes in the joists were exactly in line *and* if you drilled an access hole in the end wall in order to feed the pipe in straight.

The point about plastic pipes is that they're flexible enough to allow you to feed then in without having a straight run.

[js.b1]

There is coiled copper... but unfortunately it work hardens, holes would again need to be drilled inline accurately via a simple hand made jig... and it is not exactly cheap (although not as bad as plastic coated).

[Roger Mills]

There's coiled copper in small sizes - but in 22mm?!!

[grimly4]

They'd taste awful and wouldn't bend.