22mm or 28mm

[dreww]

when running feeds/return to a copper cylinder in an indirect system from a 80btu or so boiler 4m away, which size cu pipe is the norm, 22 or 28... is there a reg for this? or do you use 22 out of boiler thru pump and flow directors and such like and then 28 to the tank??
Many Thanks

 

[JohnD]

28mm was (is) used for Gravity flow to cylinders, to encourage an easy flow.

They are mostly pumped now, so if you have an ordinary domestic cylinder, and pumped flow to it, 22mm will be enough. If you already have an old system with 28mm, no point in ripping it out, though.

 

[dreww]

cool. thanks. just a thought, is the heat output of the boiler a factor?? Would the cylinder heat up time be reduced from what it could be if I used 22 or is that not relivent on a pumped 8m total circuit. Is there something about CH HW balancing that I need to be thinking about? Thanks

 

[Agile]

22mm is fine but you need a gate valve ( with the head removed after adjustment ) so that the HW can be balanced against the CH.

Tony

 

[corgiman]

22mm is fine but you need a gate valve ( with the head removed after adjustment ) so that the HW can be balanced against the CH.

Tony

whys that tony if he is fitting a Part L compliant Cylinder the heat loss to the rads whilst its heating up wouldnt even be noticed.

 

[Gasman77]

Is he fitting a new cylinder?

 

[dreww]

yes new cylinder, feeds, valves, pump. Existing boiler fitted a year ago. reason for the work, the HW side is over 20 years old and importantley a long way from the boiler in a location that has a change of use. Plan to fit the cylinder much closer to the boiler.
Thanks for the info so far.

 

[powell30]

Did you say 80btu's??......thats about the heat output of a candle I assume you meant 80k of btu's or 24kw approx. The circ pipe size shouldn't be an issue at 22mm.

Some very large output boilers (suprima 120L for instance) require 28mm or 35mm for the circs just to ensure the heat can be stripped away quickly enough to prevent overheat

 

[dreww]

oh well at least someone is on the ball. yes 24Kw
Thanks.

 

[D_Hailsham]

22mm is fine but you need a gate valve ( with the head removed after adjustment ) so that the HW can be balanced against the CH.

Why's that Tony? If he is fitting a Part L compliant Cylinder the heat loss to the rads whilst its heating up wouldn't even be noticed.

Because, when both CH and HW are being heated, the circulating water will take the path of least resistance, which will be through the cylinder. This will deprive the heating circuit of water. It's the same reason why you balance radiators.

 

[Nordio]

Balance the HW coil with the CH.
So if a cylinder coil required 13/Lmin for optimum performance some of you guys would do a trade off with the CH.
Don't make sense.

Whatever happened to HW priority?

 

[Agile]

whys that tony if he is fitting a Part L compliant Cylinder the heat loss to the rads whilst its heating up wouldnt even be noticed.

There are two reasons why I would always advise putting a gate valve.

Firstly, the flow can then be balanced against the heating circuit.

Secondly if the flow rate is not slowed a bit the temperature differential will become too small and prevent condensing and thus lower efficiency.

The resistance of a cylinder coil is very low as its only a few turns of 22 mm tube. Reducing the flow will increase the temperature differential and also in a few cases ensure the correct operation of boiler flow switches as some dont work well with little circuit resistance.

Tony

 

[Agile]

oh well at least someone is on the ball. yes 24Kw
Thanks.

Dont worry, we all all on the ball !

Particularly Spurs after their 3:1 win last night !

Tony

 

[Nordio]

Firstly, the flow can then be balanced against the heating circuit.

And what output from the boiler does the coil receive?
Probably not much more than a couple of kw's!

Secondly if the flow rate is not slowed a bit the temperature differential will become too small and prevent condensing and thus lower efficiency.

So when HW only selected the flow is restricted to such a degree that the coil cannot reach its optimum heat transfer capability and the boiler cycles inefficiently!

What's the point of manufacturers fitting highly efficient heat exchangers into their cylinders when the flowrate to them is restricted/balanced with the CH circuit?.

 

[corgiman]

whys that tony if he is fitting a Part L compliant Cylinder the heat loss to the rads whilst its heating up wouldnt even be noticed.

There are two reasons why I would always advise putting a gate valve.

Firstly, the flow can then be balanced against the heating circuit.

Secondly if the flow rate is not slowed a bit the temperature differential will become too small and prevent condensing and thus lower efficiency.

The resistance of a cylinder coil is very low as its only a few turns of 22 mm tube. Reducing the flow will increase the temperature differential and also in a few cases ensure the correct operation of boiler flow switches as some dont work well with little circuit resistance.

Tony

Thanks for a concise and informative post tony