My sheet has cells whose values are determined by the result
of an IF formula, eg

=IF(LEFT(F20,3)=I$5,$G20,0)

I want to have a total of each colum but when I insert a SUM
formula it gives a 0 result. I thought it might be something to do
with the calculation order but I don't know how to change this.

Any ideas how I can get this to work?

Thanks,
Seamus