Three or four inch pellet vent for insert?

I've mail ordered 3" duravent pro for my existing chimney install of an insert. It's a ranch and I think the total length will only be about 18 feet. The breckwell manual in one section says the "equivalent vent length" for 3" should not go over 15 feet. In the section for the chimney install it doesn't mention this though.

Will 3" be OK? need to change my order soon if it isn't...

thanks,

Steve

Ah, I'm OK then. Thanks for the quick reply!

Yes, that's implied from what the manual says (ie fire may not burn well). The manual says not to go over an EVL of 15 though using 3" so it seems like I'm good with 9.

-steve