Ok, firstly your 'tiger loop' should not be installed indoors, it is an outdoor model
and would be considered an increased fire risk installed internally beside a heat source.
What the heck is the green garden hose connected to???????
And as for all the tappings off in half inch? is you system microbore?
I would guess around a 70-90k btu boiler, doesn't look a whole lot bigger, but always hard to tell for sure, but as it is sporting a riello g3b (r40) burner, well this is only rated 90k btu max anyhow.
What size nozzle is installed in it? (us/gal ph)
What fuel are you using kero or gasoil?
to 90k b