Swapping Separate Gas Ducted Heating and Evap Cooling for Central Split System?

• 

  payless69 on 24/04/2022 - 12:37

  6 outlets is a massive task. Generally split systems max out with 3 heads before getting into commercial stuff. Stick with same brand, least noise and if energy supplier allows adaptive power!

  • 

    Master Bates on 24/04/2022 - 12:55

    +4

    I think OP means ducted aircon with a single outdoor unit.

    • 

      payless69 on 24/04/2022 - 13:20

      Can be done. But if ducts are big enough they still need inspection for quality. Built up mildew requires expensive replacement.
      Nothing beats the comfort of radiator heating. Domestic cooling trends to split system use.
      If the house is huge, the ducts fine, heat exchangers can be built in and a big outdoor hvac system placed like they do in the US.

  • 

    ChrisLevo on 24/04/2022 - 14:56

    We have 9 outlets with our 12kW system and no dramas.

• 

  bloom on 24/04/2022 - 12:58

  +3

  In my case it was a no for the following reasons:
  - ducting wrong size
  - ducting had poor insulation
  - split is strongly recommended to have ceiling outlets (cold air falls)

  Get a quote and they’ll determine if any can be reused

• 

  baronorder on 24/04/2022 - 13:07

  +1

  Depending on the system you wish to go for then you will be looking at around the $7-9k mark for something reasonable in the 13KW heating / cooling range for a single phase system. It really depends highly on how large and well insulated / thermally efficient your home is and what your current bills are as to if this would make sense to replace an existing gas / evap system as its a very effective combination on both ends of the heat spectrum.

  Also you need to be careful with the "heating" rating of reverse cycle systems as nearly all are hopelessly optimistic on their marketed rating when it comes to their heating performace when outdoor temps get really cold as its a very different experience compared to a ducted natural gas system. For example most ducted gas systems are rated anywhere between 15 and 35+ KW of output and will pump that out almost instantly regardless of outdoor temps.
  However a reverse cycle unit is highly dependant on the outdoor temp for its efficiency and the colder it gets, the less effective it is at pulling in heat and more energy is required to try to "defrost" the system or run resistive heating boosters.

  For example in Canberra where -6 or below is pretty common in winter most large reverse cycle units really struggle to work as effectively as their rating would imply and either keep going into defrost mode or start needing to turn on large boosters to try and get some heat flowing.
  Its a common complaint in cold climates when people replace natural gas with a ducted reverse cycle unit and is something that most installers will not make people aware of pre-purchse. You should be OK in Melbourne where it doesn't get down below -2 much but it is something to keep in mind when sizing the system.

  • 

    jollster101 on 25/04/2022 - 12:43

    I was thinking (unfortunately) that cost could be as high as what you have suggested. If it was then despite the comfort level it would be a hard sell I reckon. We have a pretty well insulated house with R3.5 batts in the roof that I put in so I know it was done properly although just the standard R1.0 blue paper stuff in the walls from when it was originally built by the previous owners. I also replaced all the heating ducting a few years back with R1.5 insulated runs so that would be helping to keep the efficiency a bit higher.

    Based on that the bills aren't ridiculously high. Will get a quote and see what comes back.

• 

  mini_wombat on 24/04/2022 - 13:24

  +9

  I am just in the process of doing this. I have a 1985 old Brivis Buffalo gas ducted system which I replace with 2 split systems in 2 weeks.

  Step one:
  Draught proof the hell out of your house - draught proofing helps so much:
  - Changing downlights to IC4 rated closed LED lights (which can be covered with insulation) : Example: https://www.sparkydirect.com.au/p/Clipsal-TPDL1C2-LED-Downli….
  - All windows and doors fitted with draught proofing - you will be surprised how bad some are: I used: https://ecomasterstore.com.au/collections/diy-draught-proofi…
  (expensive but good quality)
  - Gap seal all skirting board holes and floorboards with silicone or gap seal: this one is great: https://ecomasterstore.com.au/collections/draughtproofing-ga…
  - check all services penetrating the walls and seal them (water pipes, drains, cables for wall mounted TVs, aircon pipes and cables)
  - Backdraft stoppers on all vents (bathrooms and toilets) Example: https://tighthouse.com.au/collections/draught-proofing/produ…
  - There are some hidden spots like the return air box , the gap over the fridge or sometimes the top of the interior wall plaster in the attic.

  Your Evap cooling might be an issue in winter - as it is pretty much a large hole in your thermal envelope. Also by sealing all your house the efficiency of the system might go down in summer. As you are in Melbourne the benefits in winter should outweigh the loss of the Evap system in summer as you get a split system to cool down your home which works well. So it should make sense to remove the Evap system - at least make sure you seal up all the vets in winter - the warm air disappears there.

  Step 2: Insulate your house! And do it properly.
  You get the best value by insulating the ceiling properly. This saves so much money in regards to heating costs - it halfed our gas bill!!!
  It's usually possible to do this as DIY - https://www.youtube.com/watch?v=Bk2l-H-ROPI
  You can rent a thermal camera to find the spots which are not done properly. Even when you think you have insulation check it - in a lot of cases it's not installed properly, missing or just not enough R value.
  Depending on your house you also can do the underfloor and walls - both good for comfort

  Double glazing (thermally broken window frames are important too!) would be great but it's pretty expensive - a cheaper workaround is pelmets or cellular blinds. (ceiling is the most important!!!)

  Step 3:
  Now as your house is draught proofed and insulated you have it much easier to change to a lower powered split system. The less power a split system has the more efficient it gets. Check the spec sheets and you find out! I recommend getting a split system (or multiple) instead of a ducted system. You heat up a lot of ducts - not the rooms. I am getting a 6KW system in the open plan living room and a smaller 2.5KW system in the front of the house - it will always depend on the orientation of the house, insulation, size and floorpan. But as you have a double story and 6 outlets upstairs you might need a different solution. You could start by asking help at the Facebook group below … there are lots of clever people which can direct you. For such a big house you might get an expert in to do an energy audit.

  Pricing wise a 6KW system costs you around $1600 and a 2.5KW system around $900. (+ install depending on your situation).

  Step 4
  Closing the old vents - After installing the split systems you can close up all the old ducts of your old gas heating (improving the thermal envelope of the house even more).

  Step 5
  Invest in a solar system.

  Some more info:
  https://www.facebook.com/groups/MyEfficientElectricHome
  https://www.youtube.com/c/EfficiencyMatrix
  https://www.youtube.com/c/ecoMasterAu
  https://www.yourhome.gov.au

  • 

    HardQuiz on 24/04/2022 - 16:44

    Great overall advice here. Thank you!

    • 

      jollster101 on 25/04/2022 - 12:48

      Agree, thanks for the really detailed reply. I replied to an earlier comment with some detail that covers some of the stuff you mentioned.

      We have solar already but its only a 2.1KW system that we put in ~8 years ago. I did contemplate upgrading it when the current inverter dies so will see what the cost is there at the time. I think that unfortunately we wouldn't be able to gather any rebates from the Vic gvt given we have an existing system.

      I will take a wander around the house and look for obvious gaps for draught proofing. I know of a couple of areas in the kitchen but I don't know that I can get to them because of kitchen cupboard carcasses that are in the way.

      The links you provided are great, thanks for those. I will trawl through them.