Question about adding heat source for older home

[Brian H.]

Found a property built in 1926. It is rented as a triplex with possible great cash flow.  It does not have a permanent source of heat. I guess people buy heaters? That's not something I want in a property I own. In a property like that, what is the best option for a permanent heat source? Adding forced air heat would be crazy expensive, right? I just hate baseboards because of the potential of fire from carelessness.