Oil Furnace does not heat the rental rooms very well.

[Devin Cutler]

So, my house is set up with just an oil furnace, each winter we have struggled to keep the rooms on the other side of the house warm. Now we have renters moving into those rooms, (we moved into the low portion of the house) and I am nervous about how I should heat them, I want to add electric wall heaters with thermostats to maintain 72F but I am afraid the tenants will get crazy with the heat and I will be stuck with the bill. Does anyone have some advice on an economical way to address this issue? I know that the burner in the furnace is brand new, and it does heat most of the house but not all of it.