"John Keith" wrote in message

What exactly is meant by a "mechanical door"? My friend thought this
implied a door with a closer attached to it but I've never seen a
residential utility room door with a closer.

Check your local code. It may require a fire rated door. The new boiler
should also have an outside air intake for combustion air.

Next steps lacking any feedback will be to probe the HVAC installers
for more detail and/or call the city building inspector for more
insight. I assume a permit was pulled for this job and if so shouldn't
the installer finish the job to meet any inspection?

Thanks for any insight.

They may have pulled a permit for the install of the boiler. That is all
they are required to do. They have no responsibility for the door, use of
adjacent area, etc. That is up to the building owner to comply with codes.
If he has bedrooms in the area he should also check the code for other
requirements, such as a means of egress.