Pipework and Flowrate

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Hi,

I've been having a bit of problem with rads at end of circuit taking a while to heat up. I've recently replaced them and balanced them as best as I could.

I still have the issue and began investigating the pipework I have found a small section on the flow and return that goes from 22mm to 15mm to 22mm. Now this just doesn't seem right and I'm guessing may not be helping with rads at the end of the circuit am I correct in my limited plumbing ability?

Thx
 
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Not usually done, but it may be OK if the 22mm after the 15mm doesn't really need to be 22mm, i.e it's carrying less wattage so could be 15mm.

Can you see any obvious reason why the 15mm has been inserted.

When you replaced the rads, did you rebalance the whole system or just the replacements?
 
the section that has the 15mm tees off to feed a rad in one of the bedrooms.

The section after where it returns to 22mm feeds the bathroom and the rest of the downstairs radiators. The radiators i replaced were all downstairs so i have left them open as there at the end of the circuit.
 
the section that has the 15mm tees off to feed a rad in one of the bedrooms.
I take it you mean like this:

(Sorry for the diagram; sketching is impossible on this site.)

22mm
15mm

[code:1]
||
||
=====================
[/code:1]

All I can think is that the installer did not have any 22/15 Tees, but he did have 22/15 straight couplers and 15mm tees. How long is the 15mm pipe between the two 22mm sections?

The section after where it returns to 22mm feeds the bathroom and the rest of the downstairs radiators.
How many rads does it feed?
Approximately how old is the heating system?

The radiators i replaced were all downstairs so i have left them open as there at the end of the circuit.
So you didn't balance them. :rolleyes:
 
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the diagram is spot on :) it feeds 7 rads downstairs around 9Kwh in total. The boiler is two years old a bosh worcester greenstar 30cdi. Ive not attempted a full rebalance with the new rads in place.
 
Close consideration needs to be given to the Delta T & Delta P when pipe sizing. These factors can have a huge bearing on the outcome of the size of tube used.

Also there's the materials used, plastic tubing has a vastly reduced bore.
 
Close consideration needs to be given to the Delta T & Delta P when pipe sizing.
Agreed; but it's only feasible when installing a brand new system. If just the boiler is being replaced you are stuck with the existing pipes which, in most cases will have been sized for a 10C/11C Delta T.

For the benefit of readers who may not know, Delta T is the difference between flow and return temperature at the boiler, and Delta P is the pressure drop round the system. Both are affected by the flow rate. Delta T increases as the flow rate decreases; but Delta P reduces as the flow rate decreases.

As for the OP's specific problem, the WB 30CDi boiler is designed for a 20C Delta T. If the system is commissioned with a 20C differential, a 15mm pipe is able to carry 12kW, so 9kW will not cause any problems.

Balancing the system need to be done, before trying anything else.

Do you have the Combi, Regular or System version of the boiler?
 
I have a regular wb cd30i combi interesting about the deltas. I may of been conservative on 9kwh I'm going to check the kWh on each.
 
Close consideration needs to be given to the Delta T & Delta P when pipe sizing.
Agreed; but it's only feasible when installing a brand new system. If just the boiler is being replaced you are stuck with the existing pipes which, in most cases will have been sized for a 10C/11C Delta T.

For the benefit of readers who may not know, Delta T is the difference between flow and return temperature at the boiler, and Delta P is the pressure drop round the system. Both are affected by the flow rate. Delta T increases as the flow rate decreases; but Delta P reduces as the flow rate decreases.

As for the OP's specific problem, the WB 30CDi boiler is designed for a 20C Delta T. If the system is commissioned with a 20C differential, a 15mm pipe is able to carry 12kW, so 9kW will not cause any problems.

Balancing the system need to be done, before trying anything else.

Do you have the Combi, Regular or System version of the boiler?

Oh but surely DH, all the course cowboys, chancers & so called heating experts, that this forum is awash with. They'll completely understand what you're talking about & be second nature to them all!!
 
I have a regular wb cd30i combi interesting about the deltas.
You can have a regular (open vent with separate HW cylinder), or you can have a combi; but I know what you mean. Just makes balancing a bit more complicated.

I may have been conservative on 9kwh I'm going to check the kWh on each.
If you don't know the brand but they are typical steel rads (not designer types), it doesn't really matter. Just use the figures from any reputable manufacturer, e.g Stelrad.

If you can size all the rads in the house and provide the info, it would be helpful.

Does your house get warm enough in the coldest weather?

Lastly, use Whole house boiler sizer and provide the figures.
 

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