System boiler kw sizing and expansion vessel

[meakinsl]

If we had an idea of system volume I could calculate for you a suitable size. As Shaun says though oversizing a vessel will never cause a problem but an undersized vessel/vessels will.

Many thanks, for my understanding is the additional tank in addition to the integral tank or does the additional one bypass it ? From everything read and from replies no idea why plumber would think that 7L is enough,

Lawrence

 

[SJB060685]

You would need an additional tank as well as that within the boiler.

 

[John.g]

A 7Ltr EV with precharge/filling pressures of 1.0/1.5 bar with mean rad temps of 70C will accomodate a system volume of 75 litres with a final pressure of 2.53 bar.
A 7Ltr EV with precharge/filling pressures of 0.8/1.3 bar with mean rad temps of 70C will accomodate a system volume of 85 litres with a final pressure of 2.48 bar.

 

[meakinsl]

You would need an additional tank as well as that within the boiler.

Cool thanks, so looking like need about 15 overall so would need an additional 8L external vessel to cover things,

Many thanks,

Lawrence

 

[John.g]

If room allows why not install a 15/18 litre, if the internal one then fails, the boiler PRV will not lift and you can replace it (if ever) at your leisure.

 

[meakinsl]

If room allows why not install a 15/18 litre, if the internal one then fails, the boiler PRV will not lift and you can replace it (if ever) at your leisure.

Thanks for advice, boiler is in garage so not constrained on space so can go bigger which sounds like no downside,

Many thanks,

Lawrence

 

[SJB060685]

Cool thanks, so looking like need about 15 overall so would need an additional 8L external vessel to cover things,

Many thanks,

Lawrence

Again, without an idea of system volume we're just guessing but an educated guess suggests a 15/20 litre will be more than enough. As we've discussed too large a vessel is not going to cause system function problems and will also hold a certain amount of reserve water should the system need it, the only downsides to oversizing a vessel are additional cost being larger and space but you said above space is not an issue and there's not going to be much of a difference in cost.