Pipe sizing - Replacing a one pipe system with flow and return

[Fwds2andback]

Incase anyone is interested.
For UFH pipe sizing i'd use a temp differential of 10 or less

Thanks again Knappers. Once again I appreciate you taking the time. I guess I’ve been a bit spooked as currently the last 5 rads in the back half of the house do not heat up and apparently never have to any great degree. I believe this is most likely due to it being a one-pipe system though and hopefully not due to pipe sizing. The HW cylinder is 7m away from the boiler and plumbed in 28mm which I reckon could be a legacy thing from an old system. Whereas the CH is in 22mm. The current oil fired boiler is a Grant Vortex Utility 26-36 which again I reckon is over spec’d due to the old one pipe system. I intend to replace the boiler next year with a gas one by someone suitably qualified. Everything I’ve read suggests that replacing a one-pipe (albeit with a by-pass under each rad) with a two pipe will be worth my while in terms of efficiency. Does all of the above sound like sound logic or am I barking up the wrong tree? Thanks again

 

[Knappers]

What do you mean when you say a bypass under each rad?
One-pipe systems can be temperamental especially if modified and modern hardware doesn't often work well with them.
You will have much more control over the system with 2pipes and you can use modern TRVs etc effectively.

 

[Fwds2andback]

What do you mean when you say a bypass under each rad?
One-pipe systems can be temperamental especially if modified and modern hardware doesn't often work well with them.
You will have much more control over the system with 2pipes and you can use modern TRVs etc effectively.

The feed for the rad is a 22mm it then reduces to a 15mm tail and a 15mm pipe that runs under the rad. This pipe then meets the other rad tail reducer and goes back up to 22mm …. on some rads. On others there is no bypass. Hope that makes sense?

 

[tamzbackforalook]

Will be fine on 22mm but if you want to future proof a bit 28mm would be best and tee off in 22mm when there a run of 2 or more rads

I see you have never really gotten any cleverer with your answers

 

[ShaunCorbs]

I see you have never really gotten any cleverer with your answers

How far would you like me to go in-depth most of the time it’s lost on a diyer so tend not to confuse them

 

[tamzbackforalook]

How far would you like me to go in-depth most of the time it’s lost on a diyer so tend not to confuse them

Fill your boots. I'd be interested to see if you are learning

 

[ShaunCorbs]

Well 22mm can carry 0.29lps which works out to around 24kw at dt20 with a 0.9mps flow rate

28mm will carry 0.49lps which works out to around 40kw at dt20 with a 0.9mps flow rate

Now with England recommending you start sizing your Emitters for a flow of 50dc eg dt20 rads eg ready for heat pumps your pipework needs to be sized the same

For example

22mm will carry 6kw with a dt 5 on water and 5.4 on gycol
28mm will carry 10kw with a dt 5 on water and 9.2 on gycol

 

[tamzbackforalook]

Well 22mm can carry 0.29lps which works out to around 24kw at dt20 with a 0.9mps flow rate

28mm will carry 0.49lps which works out to around 40kw at dt20 with a 0.9mps flow rate

Now with England recommending you start sizing your Emitters for a flow of 50dc eg dt20 rads eg ready for heat pumps your pipework needs to be sized the same

For example

22mm will carry 6kw with a dt 5 on water and 5.4 on gycol
28mm will carry 10kw with a dt 5 on water and 9.2 on gycol

Keep going

 

[ShaunCorbs]

Keep going

For that I would need pipework lengths / runs and emitter loadings which op doesn’t state and tbh not worth it on a free forum your more than welcome to spend your time on it though and send a full report to the op eg emitter sizing and pipe pressure losses/ pump head required etc

 

[tamzbackforalook]

Can't be bothered but you should change your numbers on your calculating base.
But what do i know. I'm retired

 

[tamzbackforalook]

How many boilers come with 28mm F&R these days and water is not compressable?

 

[ShaunCorbs]

How many boilers come with 28mm F&R these days and water is not compressable?

Same as why most heat only come with 15mm gas doesn’t mean I can run it straight from the meter in 15mm 20m etc (at 15kw)