And ... you will need to have adequate ventilation to furnace
enclosure, which local officials can specify to you. They can also tell
you what you need for fire-retardancy of surfaces "visible" to
heat-sources in there- with emphasis on the area above.

Bear in mind that future equipment service may include R&R of major
items. E.g. the furnace. You might be well advised to plan now for any
water that might be released in there- maybe even provide drainage.
DAMHIKT.

HTH,
J