Does that oil-burning heater need oxygen? If it does then it needs ventilation, air movement in/out of the house, pushing that 90% efficiency number way down.
Efficiency wise, the comparison between a heat pump and a furnace depends on the outside temperature. Heat pumps lose their efficiency for high ∆T, so for winter in a Russia, a furnace is likely the better option
90% is overtall efficiency including losses due to ventilation. Such system with its heat exchangers is not cheap, but long term it pays off compared with less advanced heater.
