In the past diesel units were not a good choice for "continueous" indoor applications because of the "sooty" smoke and fumes they emitted. The newer diesels equipped with catylitic mufflers are doing a lot better at reducing the NOX emissions as well as the smell. Proper and adequate ventilation is a must!! as with any internal cumbustion engine. Fresh air must be coming in at all times, exhausting the bad air. Proper and regular maintenance on diesel units is important to keep away "pre-CAT" exhaust leaks and rich or incomplete combustion issues.

I would NOT recommend using diesel units in a "Closed" type building or warehouse unless it had an "Air exchanger" type of ventilation system.