Oil Column Heater or Reverse Split System for Sydney House

We have bought a 20 years old house in Sydney. It has two installed split system AC. The AC do warm the rooms quickly, but we would like hot air in more rooms.
1) Ducted AC :: Too expensive. Also, we already have 2 split AC, so better to install split in other rooms.
2) Split system AC :: Seems the most sensible and the cost effective way or running.
3) Oil heaters :: Use them for the time being, till we get a good deal on Split system .

What do you guys recommend ?
What is the Return on investment of Split system vs Oil Heaters ? Worth to just rush in with split system now ?


  • +11

    Oil heaters will cost 5 times as much to run for the same amount of heat.
    Reverse cycle AC is the least expensive heating.

    • +1

      Few reverse-cycle AC units will achieve a COP of 5 even in Sydneys mild minimum design ambient temperatures (off the cuff I belive 6.3'C is comfort design criteria for Sydney), so that's probably stretching it a bit. You would probably expect to see real world performance equal to a COP of about 3.5 during winter nights.

      But yes, in terms of energy generation (electrical input versus heat output), reverse-cycle AC can't be beat.

      However, efficiency of distribution must also be considered. Most reverse-cycle AC systems utilise forced convection, which just heats the air in the home as opposed to the "mass" of the home itself. This can work OK in a buttoned up room with relatively low ceiling heights, but in a drafty home, a large room that is open to adjacent spaces, a room/home with high-ceilings, or - worst case - in a lower-level room that is adjacent to a staircase that leads to an upper level, the warm air will stratify and it will be hard to keep the generated heat within the confined space.

      Worst case scenario, you're making heat at a COP of 3.5, but its completely ineffective and you're just chewing up electricity for nothing.

      Conversely, oil heaters rely primarily on radiant heat, which is proximety based and much better at keeping heat close to the floor. In some situations where a home has the aforementioned issues, it can be more efficient to use this for local comfort than to use reverse-cycle AC…even though any plug-in electric heater can have at-best a COP of 1.

      It sounds like it's out of the OPs budget (and potentially infeasible to install being an existing home), but the best of both worlds is a hydronic ("air to water") heat pump that uses reverse-cycle AC to create hot-water for radiators or hydronic underfloor heating (and would also do your potable water heating to boot). Even above that is a ground-source heat pump ("water to water"), which can achieve COPs in the 7's regardless of ambient conditions - but now you're talking beaucoup and beaucoup bucks.

  • +1

    I'm in the similar predicament.

    I installed 4 brand new split systems a few years ago. I find the AC heat function very drying to my skin.

    So im opting a column heater to keep my bedroom warm during the night.

    Hope that helps somewhat :)

    • Thanks. Very helpful

    • +1

      You have a heater on when you are under the covers in bed in Sydney's climate?

      • yup! i have timber flooring so its actually really cold >.<

        Today was like 9 degrees in the morning.

  • Oil heaters are near silent (they might creak and bang a little as the metal expands/contracts), so might be more useful in a bedroom if noise is a concern, but then also don't cool in summer.

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