Chests of heavy smokers by the sound of it (7)

I believe the answer is:

coffers

I'm a little stuck... Click here to teach me more about this clue!

'chests' is the definition.
(I know this)

I cannot understand how the remainder of the clue works.

(Other definitions for coffers that I've seen before include "Money-chests" , "Treasury boxes" , "Financial resources or money boxes" , "Funds, financial resources" , "Treasury funds" .)

I've seen this clue in the Sydney Morning Herald.

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