How much do duct reducers effect airflow?

How much do duct reducers effect airflow? Specifically a 6 inch 400cfm inline fan with a 6"-4" reducer? Asking because tent hole is smaller than my fan and hood.

Zorak said:

How much do duct reducers effect airflow? Specifically a 6 inch 400cfm inline fan with a 6"-4" reducer? Asking because tent hole is smaller than my fan and hood.

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Not exactly yhe answer your looking for but i connectwed a 6 inch fan with reducer to a 4 inch carbon filter my room temps were too high so i took off the filer and reducerr and it easily keeps temps down now.

Still more effective to have a 6 inch with a 4inch reducer than a straight 4 inch imo.

Why not make the hole bigger?

are you pulling or pushing air with it? pulling shouldn't hurt, in fact it should increase velocity a little( if my math is right).

Just the duct reducer by itself shouldn't really affect your airflow.