Especially because all tenants wait until the last minute so all the HVAC contractors end up with a 2 week wait list where tenants have no AC or heat depending on season.

Whose paying for the heat? 

When those spaces are properly permitted to be living space, they then appear as 'finished' spaces and are reflected in the 'heated' or 'living' square footage. 

As Chris added, fire escape, AC/heat ducting. 

Atleast that way she’s heating the house for me

Taking $50-100 less per month on a 6-8 month lease is less than one full month of vacancy, not to mention added costs of vacant maintenance (heat, security, etc), so it is a no-brainer.I would suggest you see what the market rate is *right now* for units similar in location, size, and amenities to yours, and then consider taking 5-10% off of that figure, and go until late spring/early summer with the lease.

Nope, just your basic heat pump.   

A couple of things I have thought about are adding heat to the warehouse as it is currently not heated and I've got a bathroom and laundry that are on the same level as the warehouse.

You found the tiles and there is more; but it is not a big deal, unless for example, there is a forced air heating system and you decide to do an extensive re-model.

Basically the first thing that goes wrong will probably cost $500 just in materials -- think water heater, sink, heating unit, etc.