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

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.

Reply to
Colin Stamp
Loading thread data ...

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

Brian

Reply to
Brian Gaff

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

Cheers,

Colin.

Reply to
Colin Stamp

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.

Reply to
newshound

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...

Reply to
Dave Liquorice

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

Reply to
John Rumm

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

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.

Reply to
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.

Reply to
Colin Stamp

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.

Reply to
Colin Stamp

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

NT

Reply to
meow2222

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.

Reply to
Colin Stamp

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.

Reply to
Roger Mills

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.

Reply to
Colin Stamp

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.

Reply to
Roger Mills

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.

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.

Reply to
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.

Reply to
Colin Stamp

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.