In Greece the heating oil went up to 1.20 Euros. Meaning that is WAY too expensive to burn. Therefore, I look for alternatives and the used olive/vegetable oil from local souvlaki/gyro store seems more appealing as alternative fuel.

But what modifications needed in order to use filtered used cooking oil to my central's heating burner? Usually the most common fuel for central heating is the red diesel, but that priced over 1 euro made it too expensive.

Central Heating in Greece use diesel to heat water and that is circulated to heating elements where heat is emitted.

Of course prior to use I'll filter it using cloth and possible stoned and sand before filling my diesel tank with used cooking oil. Also, filtering oil is cheaper than making it into biodiesel (requires no heat).