Central heating long lengths of 15mm

[EAST61]

The difference is that Option 2 short circuits all of the radiators and will be the path of least resistance - meaning water will always try and flow through that path rather than where you want it to go (i.e. through the radiators).

Ok thank you

It makes me wonder why we bother using 22mm at all though, if it's going to be bottlenecked by 15mm at the end of the run, why don't we just do the whole thing in 15mm?

 

[fezster]

Ok thank you

It makes me wonder why we bother using 22mm at all though, if it's going to be bottlenecked by 15mm at the end of the run, why don't we just do the whole thing in 15mm?

Because you have multiple radiators coming off of a 22mm "trunk". There's a maximum BTU a 15mm pipe can deliver. I think the rule of thumb (something I read on here many years ago) was a maximum of 3 "average sized" radiators from a 15mm pipe.

Pipe length and resistance also comes into it. The longer the length of pipe, the more resistance it has. Using a larger pipe reduces this resistance.

 

[D_Hailsham]

The difference is that Option 2 short circuits all of the radiators and will be the path of least resistance - meaning water will always try and flow through that path rather than where you want it to go (i.e. through the radiators).

Balancing would be impossible if Option 2 was used.

 

[EAST61]

Balancing would be impossible if Option 2 was used.

Good point.

The penny just dropped for me with regards to how balancing works. Thank you.

 

[Terry lambert]

Some rads are more average than others, what is an average rad ? If It was at the end of a large system you could run out of pump head

If velocity through the pipe is too slow you can get other issues

 

[Pin 5]

Im not sure about how velocity being too slow on a sealed system is detrimental.

 

[Steelmasons]

Im not sure about how velocity being too slow on a sealed system is detrimental.

 

[Terry lambert]

Im not sure about how velocity being too slow on a sealed system is detrimental.

Yeah, okay

 

[Pin 5]

Lets not be shy @terrydoh . If we had a typical 600 x 600 type 11/k1 with a flow and return dt20 pipe in 15mm would we have an issue?

 

[Terry lambert]

On 50 meters of pipe, fittings with a high resistance hex and 6 metre head pump you may struggle

No need to be bashful

What's the target design velocity for central heating ?

What's the method for pipe sizing ?

 

[Pin 5]

Wasnt being bashful. Your reply of "yeah okay" started this.

Would always look to design a system around 1m/s velocity with a max of 1.5m/s minimum 0.5m/s (although my example showed 15mm would be well oversized for this).

Pipe size would depend on kw required, length of pipe number of bends fittings etc, type of pipe used.

 

[Terry lambert]

So velocity can be too slow then ?

 

[Terry lambert]

cant be bothered

 

[Pin 5]

Typical 600 x 600 single panel would be approx 600w with a Dt20 n 15mm that would be approimatley 0.05m/s through that size pipework. A tad low one might say.

With less that 0.001 m head resistance per m I reckon my rad would be ok on 50m of pipework and a high resistance hex

 

[Terry lambert]

just a tad