Fireplace duct

[James R. Szczesny]

This duct was coming down from a gas fireplace insert that was vented through the chimney, there was a draft going thru the fireplace. What could this be for, clearly it is not installed correctly laying on the crawlspace floor. Have any ideas?

[Barry Adair]

many mfr. & ahj require

Prefabricated Fireplace Air Supply:
Prefabricated fireplaces must have fresh air supply direct to exterior of dwelling.

crawl space supply is ill advised and i would note as a deficiency/repair

[KEVIN WOOD]

It may be a supply to keep the crawlspace area warm. This will need to be checked when the fireplace is running for some time to get the sensor to start the blower.
If it is an air intake Barry is right and it cannot be taken form inside the dwelling.