Would I be mad to use 10mm plastic pipes for radiators?

[Colin Stamp]

Hi all,

For various reasons, I want to replace the downstairs radiators on my
1970ish Y plan heating system, along with their plumbing. There are
currently four large radiators downstairs. I'll be adding more when I
get to work on an extension in the spring but, for now, I just want to
replace those four rads.

My current plan is to run "backbone" pipework in 22mm plastic from the
controls in the airing cupboard, through the floor void to each of the
rad positions. I'd do the drops from the backbone to the rads in 10mm
plastic to make installation quicker and to keep the chase depth down to
a minimum.

Does this sound like a really stupid thing to do? A quick look online
seems to suggest that opinion is divided on plastic in general and 10mm
in particular...

Cheers,

Colin.

[Brian Gaff]

Gonna be harder to find plastic if you want to drill the wall!

Brian

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From the Sofa of Brian Gaff Reply address is active
"Colin Stamp" <dus...@stamp.plus.com> wrote in message
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[Colin Stamp]

On 23/01/2013 13:23, Brian Gaff wrote:
> Gonna be harder to find plastic if you want to drill the wall!
>
> Brian
>

Good point. I think you can get metallic tape. Otherwise I'll use steel
capping.

Cheers,

Colin.

[newshound]

Assuming you use pipe on a coil, you are going to need steel capping to
keep it in place prior to replastering.

FWIW I just replaced some 10 mm copper drops with 15 mm copper, boxed
in, because of inadequate flow on the 10 mm. Part of that though was a
blockage which I never located, either from solder or from a flat or
kink in the copper somewhere.

[Dave Liquorice]

On Wed, 23 Jan 2013 14:02:11 +0000, newshound wrote:

> FWIW I just replaced some 10 mm copper drops with 15 mm copper, boxed
> in, because of inadequate flow on the 10 mm.

This is well worth noteing, the wall thickness of plastic is higher than
copper. How big is the ID of 10mm plastic, can't be much...

--
Cheers
Dave.

[John Rumm]

On 23/01/2013 14:02, newshound wrote:
> On 23/01/2013 13:39, Colin Stamp wrote:
>> On 23/01/2013 13:23, Brian Gaff wrote:
>>> Gonna be harder to find plastic if you want to drill the wall!
>>>
>>> Brian
>>>
>>
>> Good point. I think you can get metallic tape. Otherwise I'll use steel
>> capping.
>>
>> Cheers,
>>
>> Colin.
>>
> Assuming you use pipe on a coil, you are going to need steel capping to
> keep it in place prior to replastering.

A clout nail either side of the pipe every so often will also do the job..


--
Cheers,

John.

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[Colin Stamp]

On 23/01/2013 14:02, newshound wrote:

> Assuming you use pipe on a coil, you are going to need steel capping to
> keep it in place prior to replastering.

Yep. It'll certainly need something. Steel capping looks like the best
bet to hold it down and make it detectable.

>
> FWIW I just replaced some 10 mm copper drops with 15 mm copper, boxed
> in, because of inadequate flow on the 10 mm. Part of that though was a
> blockage which I never located, either from solder or from a flat or
> kink in the copper somewhere.

This is the main worry for me. JG reckon 10mm is good for nearly 2kW at
11C drop. They don't say what length of pipe that's for though...

Cheers,

Colin.

[Colin Stamp]

Indeed - it won't be much. The big question is, does it need to be much?

My previous house had some pretty big rads on 8mm copper, with much
longer runs than I'm planning, and the system worked fine for the 13
years we lived there. I wonder how 8mm copper compares to 10mm plastic.
I need to do some more digging...

Cheers,

Colin.

[Colin Stamp]

On 23/01/2013 15:59, John Rumm wrote:
> On 23/01/2013 14:02, newshound wrote:
>> On 23/01/2013 13:39, Colin Stamp wrote:
>>> On 23/01/2013 13:23, Brian Gaff wrote:
>>>> Gonna be harder to find plastic if you want to drill the wall!
>>>>
>>>> Brian
>>>>
>>>
>>> Good point. I think you can get metallic tape. Otherwise I'll use steel
>>> capping.
>>>
>>> Cheers,
>>>
>>> Colin.
>>>
>> Assuming you use pipe on a coil, you are going to need steel capping to
>> keep it in place prior to replastering.
>
> A clout nail either side of the pipe every so often will also do the job..
>
>

I've used hot melt on cables in the past. I guess I'd run into trouble
here unless I remembered not to use the rad until after the plaster had
gone off...

Cheers,

Colin.

[meow...@care2.com]

On Wednesday, January 23, 2013 4:26:16 PM UTC, Colin Stamp wrote:

> JG reckon 10mm is good for nearly 2kW at
> 11C drop. They don't say what length of pipe that's for though...
> Cheers,
> Colin.

It also depends on how many elbows, what pump speed and what temp drop.


NT

[Colin Stamp]

Yep - there's certainly not enough info to be definitive. It's to be
hoped that they've chosen sensible, moderate values for all the
variables. In that case I should be OK, since only the drops from
ceiling to radiator will be in 10mm. Surely that would be about the
minimum flow-resistance common set-up you could expect.

Then again, maybe they've assumed a 10cm section of perfectly straight
pipe...

Cheers,

Colin.

[Roger Mills]

On 23/01/2013 16:26, Colin Stamp wrote:

>
> This is the main worry for me. JG reckon 10mm is good for nearly 2kW at
> 11C drop. They don't say what length of pipe that's for though...
>

Not sure that length is an issue - within reason. The limit is usually
based on keeping the water velocity below the level where it starts to
get noisy.
--
Cheers,
Roger
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[Colin Stamp]

On 23/01/2013 22:32, Roger Mills wrote:
> On 23/01/2013 16:26, Colin Stamp wrote:
>
>>
>> This is the main worry for me. JG reckon 10mm is good for nearly 2kW at
>> 11C drop. They don't say what length of pipe that's for though...
>>
>
> Not sure that length is an issue - within reason. The limit is usually
> based on keeping the water velocity below the level where it starts to
> get noisy.

With an @11C drop and 1.95kW, they quote the velocity as 1.2m/sec. Not
sure how noisy that would make it, but I'm still more concerned about
the length. They give the pressure drop as .283 m/m, so my 5m pump will
run out of steam at about 17m of 10mm pipe. Presumably the flow reduces
pro-rata.

One of the rads will be close to 2kW and I reckon on about 7m of 10mm
pipe, dropping 2m, plus a couple of elbows and a few pipe inserts. I
think maybe I'm getting a bit too close for comfort here.

Perhaps chases deep enough for 15mm won't be so bad after all...

Cheers,

Colin.

[Roger Mills]

On 23/01/2013 23:19, Colin Stamp wrote:
> On 23/01/2013 22:32, Roger Mills wrote:

>> Not sure that length is an issue - within reason. The limit is usually
>> based on keeping the water velocity below the level where it starts to
>> get noisy.
>
> With an @11C drop and 1.95kW, they quote the velocity as 1.2m/sec. Not
> sure how noisy that would make it, but I'm still more concerned about
> the length. They give the pressure drop as .283 m/m, so my 5m pump will
> run out of steam at about 17m of 10mm pipe. Presumably the flow reduces
> pro-rata.
>

The JG figure will assume that you're using a pump with sufficient grunt
to supply the required pressure and flow - which may or may not be the
case in reality!

If you look at the spec of your 5m pump, that's probably 5m at zero
flow, with a curve going down to a high flow rate at zero pressure.
Ideally, you want to be running it somewhere in the middle of that
curve. So you need to look at total circuit resistance and total flow in
order to see whether it can cope. Remember that all your radiators are
in parallel - so their pressure drops are not additive, even though
their flows are.

[Colin Stamp]

On 24/01/2013 18:52, Roger Mills wrote:
> On 23/01/2013 23:19, Colin Stamp wrote:
>> On 23/01/2013 22:32, Roger Mills wrote:
>
>>> Not sure that length is an issue - within reason. The limit is usually
>>> based on keeping the water velocity below the level where it starts to
>>> get noisy.
>>
>> With an @11C drop and 1.95kW, they quote the velocity as 1.2m/sec. Not
>> sure how noisy that would make it, but I'm still more concerned about
>> the length. They give the pressure drop as .283 m/m, so my 5m pump will
>> run out of steam at about 17m of 10mm pipe. Presumably the flow reduces
>> pro-rata.
>>
> The JG figure will assume that you're using a pump with sufficient grunt
> to supply the required pressure and flow - which may or may not be the
> case in reality!

Indeed. I guess that's why they don't need to reference the pipe length.
They just give the pressure drop per metre an I can work out a sensible
length depending on how much pump I've got.

>
> If you look at the spec of your 5m pump, that's probably 5m at zero
> flow, with a curve going down to a high flow rate at zero pressure.
> Ideally, you want to be running it somewhere in the middle of that
> curve. So you need to look at total circuit resistance and total flow in
> order to see whether it can cope. Remember that all your radiators are
> in parallel - so their pressure drops are not additive, even though
> their flows are.

Yep. Guessing a bit at pressure drops for elbows and stuff, I reckon the
worst-case radiator will need about 3 metres, which sounds a bit on the
high side for a 5 metre pump to me. I'll need to wind down all the other
rads a fair bit to get the pressure up to 3m, then the flow might be
getting a bit marginal. Plus, I want to heat the water using the boiler,
not the pump ;o).

I'm leaning towards 10mm copper for the radiator drops now. If my last
system was anything to go by, that will easily be enough.

Cheers,

Colin.

[Colin Stamp]

Thanks for all the replies on this. I thought I'd post an update.

The new rads are now on, with the 22mm Speedfit backbone pipework and
10mm copper drops to the rads. I filled the system and fired it up for
the first time a couple of hours ago. There were a couple of weeping
compression joints, but all of the Speedfit stuff seems to be
watertight. After a bit of very crude balancing I have no radiator
temp-drops over 10C, even with all the TRVs wide open.

It was a bit chilly for the day-and-a-half it took to swap everything
over, but we're back up to a toasty 18.5 now. I'm dead chuffed :o)

Right - time to sweep up. There seems to be an awful lot of wall on the
floor. I think I have some plastering to do...

Cheers,

Colin.