Gravity Furnace in duplex

[Cody Barrett]

I found a duplex that needs the works.... I walked it and found an octopus style gravity furnace. At 25 yrs old I've never heard of one or seen one so I was at a lost.  All I knew was that it looked like asbestos was on it.  

So just out of curiosity what does it cost to replace a gravity furnace with 2 new furnaces that services each unit?  My other duplex has 2 furnaces so I figured that is the way to go.  It will need new ductwork too.  

thanks BP!