In the rear center of the building was a mechanical room accessed from outside by him only, between the two units.

You will most likely get a cheap 6-7mm product that has a very weak locking mechanism.

If they were to enforce it with a fine or other enforcement mechanism, they would be sued and a court would strike down the law. 

The pandemic has reshaped the way people travel, with more emphasis on remote work and extended stays.

This makes my mechanicals work less also extending their life.

A review of the term "fiduciary" is in order here, as a real estate agent (at least in MA - and I suspect in the other 49 states) is a fiduciary for their client.From Investopedia: (Emphasis is mine)What is a 'Fiduciary'Essentially, a fiduciary is a person or organization that owes to another the duties of good faith and trust.

They are similar to other mechanical systems.

I got quotes of $35,000, $40,000 and $35000.Cut out and remove the existing cast iron hot water boiler, both hot water heaters.Cut out and remove the existing 11/2"-21/2" supply and return heating mains that run from the mechanical room (back of the house) to the meter room (front of the house).Install 2- 9 port manifold stations in the mechanical for supplying heat to the cast iron radiators.Plumb the supply and return (home runs) 1/2" pex tubing for the cast iron radiators from the manifolds to the existing branch of risers in the basement ceiling.Pressure test all piping.Pipe new 11/4"x 50' gas piping from the meter room to the mechanical room.Pressure test gas piping.Install a HTP UFT 140 high efficient modulating condensing hot water boiler and a Turbomax 45 Reverse Indirect Tank (Buffer tank and Potable hot water) with near boiler piping and controls containing:The supply and return header piping from the UFT 140 boiler to the Turbomax 45 will be piped in a 2 pipe buffer tank configuration.Isolation drain and purge valves.Air and dirt magnet separators.High efficient ECM circulating pumps with isolation pump flanges.Hydronic expansion tank with support bracket.Back flow preventer and auto filer combo unit.Inline sediment and De-minerlized filter.Controls & Wiring:Low Water Cut Off.18- Manifold Actuators.Zone Control Box's.3-Thermostats with wireless sensors.Outdoor Sensor.Cold and Hot water potable water side:Isolation valves.Thermostatic mixing valve.Thermal expansion tank with support bracketPipe 3" Polypropylene and PVC flue and air intake piping from the boiler to the outside along with a thin low profile termination kit.Install a Condensate neutralizer pump and plumb the discharge tubing from the pump to the indirect stand pipe in the mechanical room.Pressure test all piping.Install and wire in all controls in the mechanical room.Power flush the system and remove any debris that is in the radiators and piping.Drain the water out of the entire system.Re-fill the entire heating system with De-mineralized water and power purge all the air out of the entire system.Set and adjust the flow meters on the manifolds as per radiators btu's output.Perform a combustion analysis on the boiler and make any adjustments if needed.

The roof seems solid, the mechanicals are newer, and no glaring defaults with the property, but I do need to have it inspected and appraised still.I cannot view the occupied unit and have only seen photos.

Crawl spaces make it MUCH easier to distribute rough mechanicals (plumbing and HVAC, mostly).