Matt, If you are looking at historically built properties such as your classic bungalows, 2-flat and 3-flats in Chicago, many of those properties were built well before the modern zoning code was established.

Making it more modern What was the outcome?

Have you thought of just renovation to make it more modern?

We added appliances and created an eat-in kitchen next to the existing galley kitchens which already had granite counters and modern fixtures.

I think what matters most is if the bathroom is nice, modern, and user friendly then either option will work. 

All modern furnaces have <20 year life span, and that is according to HVAC technicians I've spoken with.

Many times, a listing agent will use estimated rents for vacant units and those estimates might be for full rehabbed modern units where the existing unit is not near that.

The ratio of mail that wants my money, my possessions, my vote - compared to the mail that wants my time, my attention, my presence - tells me society has only two expectations for me: spend money or get out of the way.

Absolutely gorgeous property just needing modern updates.

It's crucial for electrical safety and modern compliance.Replacing a Gas Furnace: Since you're dealing with a gas furnace, the replacement cost will depend on the unit's efficiency and your home's size.