I only get its "too hard to solder the aluminum" when I start asking about putting nitrogen gas in the line before soldering. 

Did you also check if the unit are metered separately so the tenant pay for their gas, water, electric?

Currently all units are ~$50-75 below market in the zip code with water, hot water, gas heat/cooking included.Monthly gas is ~$300/month year round (higher in Winter of course, etc) and the current gas boiler/heater is 20 years old and the longest tenured tenant told me that it was on recently after a circuit breaker trip and it had to be turned off manually at the unit. 

Gas, food, office set up, taxes

It's no secret that gas prices are on the rise, with some stations charging as much as $4 per gallon. If you're ever feeling strapped for cash and need to find a cheaper station, be sure to check out the prices listed...

But, some inflation is curable, high gas prices, cost of goods ect.

Over the last couple of decades, I’ve been in the motel business, owned several c-store/gas stations and now operating several QSRs.

Increasing gas, food, commodities prices.

Meanwhile, property values more than doubled in the past ten years (pre-pandemic), rents rates doubled, and the rental market is stronger than it's ever been despite coal and gas leaving.

Currently all units are ~$50-75 below market in the zip code with water, hot water, gas heat/cooking included.Monthly gas is ~$300/month averaged year round (higher in Winter of course, etc) and the current gas boiler/heater is 20 years old and the longest tenured tenant told me that it was on recently after a circuit breaker trip and it had to be turned off manually at the unit.