Rough calculation of system water content

[TFGplumbing]

Pricing for a boiler change, custard thinking of going to a sealed system.

Boiler that i'am pricing for will require an additional expansion vessel if system is over 100 litres (its 30cdi classic system)
Its Fairly large property.

900x450 indirect cylinder on an S-plan with 11 rads

Rads

1200x600 k2
1250x600 single
1600x600 k2
1600x600 k2
1750x600 k2
1750x600 k2
1300x700 k2
950x600 k2
900x600 single
1500x600 k2
800x600 single

roughly 20Kw worth of output

Evidently its going to be hard to calculate the exact length pipe runs.

Any of you guys know a rough calculation for water capacity of systems? I'am reasonable certain that there is more that 100 litres worth here anyway

 

[mfgs]

If you go on the stelrad website, have a look at the technical info for rads and you will find the water content in litres for each one.