Sealed system expansion vessel question(s)

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i am feeling tired now too:)!!!

where do you get the pre-charge vessel pressure from? what MFR? boiler?
fitting an external expansion vessel for a heating / heating and hwsv sealed system.....
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:oops: yeah usually, but it is confusing now!!! what is the basic rule of thumb that can be applied here!!! ..... all these different calc's contradict each other!!!!!!!!!!!
Kev - sorry i have been way too annoying i know (one of those days)!!

Basically, if my house is a 3 bed semi, and the height from the vessel to the highest rad is less than 2 metres, what size (volume) vessel is OK and what charge is acceptable for it to work properley?! Last post I promise you!!!! And if I over charge it is do i need a larger size or is it still OK size-wise??

I'll assume you have panel radiators and not cast iron.

Buy 12 litre expansion vessel.
Precharge to 1 bar.
Fit to system.
Pressurise system to 1.2 bar cold.

Don't worry about height of rads etc.
You need to know the system volume.

Then you need to know the pre-charge, most boiler manufacturers say between 0.5 and 1bar.

What pressure are you running the system at 1-1.5bar is normal

Then consider the higher the pre-charge the smaller the vessel can be, but up to the manufacturers guidelines.

So lets assume you have 100Ltrs, a pre-charge of 1bar, and an system pressure of 1.5bar

Look at the chart 100 x 0.152 + the size of the vessel, if they don't make a 15Ltr vessel you go up the next size 18Ltrs

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