ideal classic lx ff 270?

i have this boiler it has a straight flu that is 20cm long and finishes on an outside wall i am looking a puting an open lean to on the back of my house and wonderd could the flue for this boiler have a 90 degree bend as it leaves the outside wall and go up another 20cm
if this is not possable could i build a u shape around the flue out of wood about 50 cm square leaving the top open

normski
August 2008