Got a question about bottlenecks, please!

[PotatoSoup]

Hiya, thanks for reading this. I'm confused about something a plumber has suggested.

He was replacing a radiator for me. He suggested by text that, as part of the radiator replacement, he could swap the 10mm central heating pipe currently supplying the radiator to 15mm pipework. I liked the idea because I've read on this forum somewhere that it could mean the radiator would heat up a bit more quickly. The ceilings are down so now is a good time for that sort of thing to get done.

The 10mm copper pipe is currently connected to a 22mm copper pipe that runs to the combi boiler.

Anyway, when he got here, he said he couldn't get to all the pipework (fine) so he could do some in 10mm and some in 15mm.

So, my question is this; (I asked him this question and he pretty much ran off so I didn't get an answer - it was a very surreal experience) what would be the impact on the time taken to heat the radiator if the pipework coming off the 22mm pipe is 10mm for about 30cms and then goes to 15mm? I would have thought the 10mm would act as a bottleneck of sorts and limit the rate of hot water passing through but that's just a guess based on my personal experience of using drinking straws!

I do understand the bloke pretty much running off because I wouldn't like to be asked that question out of the blue ...but then I've not done any physics relevant to that question for 30 years and I'm not a plumber so maybe a boffin on here knows the answer, please? I'm partly (hugely) curious to know what the answer is and I'm also partly asking to find out if it's worth asking the next plumber to change the pipework to the 15mm where possible or if I should just leave it as is. But mostly I'm just curious and in need of a kind brainiac to satisfy my curiosity...

 

[Harry Bloomfield]

The smaller and the longer a pipe is, the greater the restriction. Replacing just part of the 10mm, with 15mm, will help some, what matters is - the lengths, which will determine the improvements in flow.

 

[PotatoSoup]

Ah, ok - thank you very much!

 

[Notch7]

Hiya, thanks for reading this. I'm confused about something a plumber has suggested.

He was replacing a radiator for me. He suggested by text that, as part of the radiator replacement, he could swap the 10mm central heating pipe currently supplying the radiator to 15mm pipework. I liked the idea because I've read on this forum somewhere that it could mean the radiator would heat up a bit more quickly. The ceilings are down so now is a good time for that sort of thing to get done.

The 10mm copper pipe is currently connected to a 22mm copper pipe that runs to the combi boiler.

Anyway, when he got here, he said he couldn't get to all the pipework (fine) so he could do some in 10mm and some in 15mm.

So, my question is this; (I asked him this question and he pretty much ran off so I didn't get an answer - it was a very surreal experience) what would be the impact on the time taken to heat the radiator if the pipework coming off the 22mm pipe is 10mm for about 30cms and then goes to 15mm? I would have thought the 10mm would act as a bottleneck of sorts and limit the rate of hot water passing through but that's just a guess based on my personal experience of using drinking straws!

I do understand the bloke pretty much running off because I wouldn't like to be asked that question out of the blue ...but then I've not done any physics relevant to that question for 30 years and I'm not a plumber so maybe a boffin on here knows the answer, please? I'm partly (hugely) curious to know what the answer is and I'm also partly asking to find out if it's worth asking the next plumber to change the pipework to the 15mm where possible or if I should just leave it as is. But mostly I'm just curious and in need of a kind brainiac to satisfy my curiosity...

That’s an interesting question.

I suppose the question is once the water passes through a 10mm section does any 15mm beyond just act like 10mm.

I think a Harry might be correct, but maybe a pro can answer.

10mm layouts tend to go to a manifold I think with 10mm ports, I don’t know if having one leg at 15mm means that will get more flow than the others.

 

[terryplumb]

Why do you want to change the pipework to one rad from 10 to 15mm ?
Are all other rads piped in 10 mm ?

 

[Notch7]

Why do you want to change the pipework to one rad from 10 to 15mm ?
Are all other rads piped in 10 mm ?

I think his reasoning is this:

I've read on this forum somewhere that it could mean the radiator would heat up a bit more quickly.

 

[PotatoSoup]

That is indeed the answer!

 

[PotatoSoup]

Thanks, Notch7