New central heating system

[Jever]

Hi all,

I'm puttung in the radiators and pipework for a central heating system and the pipework is running under the screed.

The problem I have is that in some parts the screed is 50mm thick and 75mm thick in others.

In the deeper areas I reckon I can plumb in 15mm copper with the lagging on it and still get coverage with the screed.

However, in the 50mm area I don't think that will work out. A plumber suggested to me that I should switch to 10mm copper in the shallow area. Apparently you can buy 10mm pipe with a coat of lagging already on it.

A couple of thoughts here:

• If I go down to 10mm in the shallow area, doesn't that mean I will lose flow rate and need to compensate for this with bigger radiators?
• If it does come pre-lagged, what do you do if you solder in some t's and elbows? Strip it back, solder and then re-lag I guess?

TIA

Jever

 

[ianmcd]

using 10mm will restrict what size of radiators can be used and you dont want to tee off 10mm to feed another radiator, any joints in screed are a very bad idea

 

[ScottishGasMan]

The coating on the 10mm pipe is not lagging, its just a protective coating, so will still loose a notable heat into the screed, however actual lagging for 10mm will use less space than the 15mm.

If your fitting it right there wont be any tees or elbows in the screed on 10mm as your realistically not going to tee off it, and its easy to bend. as said, joints under the screed is something you want to plan to avoid to begin with

 

[muggles]

You actually get a higher velocity through a 10mm pipe than a 15mm pipe, so there isn't always a reduction in flow rate. Flow rate does not equal heat output though, it's a bit more complicated than that.

So no, you don't need to have bigger radiators for 10mm. You should, however, ensure that your radiators are suitably sized for a condensing boiler. Most radiators calculators are still working on old non-condensing sizes which will make your condensing boiler less efficient. Heating isn't just about throwing some pipes and radiators in - good system design can make a huge difference to running costs.

 

[bernardgreen]

You actually get a higher flow rate through a 10mm pipe than a 15mm pipe.

To achieve the same flow rate delivered to the radiator, ( litres per minute ) the velocity in a 10 mm pipe would have to be higher than the velocity in a 15 mm pipe.

 

[muggles]

To achieve the same flow rate delivered to the radiator, ( litres per minute ) the velocity in a 10 mm pipe would have to be higher than the velocity in a 15 mm pipe.

Sorry, tired brain, edited for clarity

 

[bernardgreen]

Sorry, tired brain, edited for clarity

I know that feeling...... too much pressure. makes the velocity greater.

.

 

[ianmcd]

You actually get a higher velocity through a 10mm pipe than a 15mm pipe, so there isn't always a reduction in flow rate. Flow rate does not equal heat output though, it's a bit more complicated than that.

So no, you don't need to have bigger radiators for 10mm. You should, however, ensure that your radiators are suitably sized for a condensing boiler. Most radiators calculators are still working on old non-condensing sizes which will make your condensing boiler less efficient. Heating isn't just about throwing some pipes and radiators in - good system design can make a huge difference to running costs.

so you are saying that a 10mm pipe with equal length as a 15mm pipe can always adequately supply a radiator that was at its max on a 15mm supply ?