My wife and I bought a commercial building and transformed it into apartments. Of course, we have the loft apartment. The other apartments are paying for our purchase and renovation of the property. It was not cheap, but nothing in New York City is. I remember us paying more for a studio apartment in Manhattan than what my parents pay for a mortgage on a farm with a house, barn and other buildings in upstate New York. We did good with our HVAC contracts in NYC to make our building compliant with the codes for residential living. These guys are geniuses. They were able to re-purpose a lot of the commercial air conditioning and heating equipment already in the building to make it comfortable for people to live there. I am amazed at the transformation.
The brick walls are really thick, and they look really good inside. They are more than one brick thick. This acts as an insulator for cold and heat. Our loft has big windows but is not drafty or cold in the winter, nor is it hot in the summer. It is just right. The HVAC system is also quiet. I remember an apartment we lived in where the sound of the AC or furnace coming on sounded like a vacuum cleaner running in another room of the apartment. Not so bad during the day, but it was very annoying when you were trying to sleep.
We are in the loft, and the company who did our HVAC work in New York sound-isolated the AC units on the roof from the roof structure. We do not hear any noise from them in the quiet of the night. The apartments were all leased before we were even done with the renovations. This investment pretty much paid for itself from the start.