We would like to eliminate gas from our house, but the most awkward phase is to find an equivalent heating system to the gas heating service that we have at present.
We have a gas fire and an hydronic system which heats a very large open space. We have one wall mounted Mitsubishi Air-con in the kitchen part of the open area living space. It is an MSZ-GL80VGD, (4.17kPa, 55W, R32), but it is almost unnoticeable in effect in the large space.
Should we purchase a Heat Pump with say 10kPa? And if so, can it be externally mounted (on the roof?) with perhaps three inside vents? Can those vents be separately controlled??
There are roof mounted units - typically intended for commercial businesses such as those found in smaller urban shopping centres or industrial estates.
These can be configured with an internal head unit like a standard split system or supplied as a ducted system with multiple service points using the roof space or on roof with insulated external ducting. There are head units that can be mounted independently in the roof space as well as integrated units that are totally outside (roof or wall or ground mounted).
Best to seek further suggestions on suppliers for your area with known reputation. Those who design and deliver ducted systems are likely to have solutions that may suit your home.
P.S.
Hydronic systems can utilise a heat pump in place of a gas boiler/water heating, assuming that option might appeal.
Don’t be surprised at how much it may cost to move on from gas. My experiences of being places that get cold, much colder than southern parts of Australia favour hydronics as one way to keep warm.
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Thanks, Mark. good info. We have a heat pump for our hot water system and that works really well. I did make some enquiries re using it for hydronic heating, to receive a negative, but perhaps uninformed response. I will make further enquiries, but if you have any leads for western Victoria, I would be pleased to follow them up.
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There are also multihead splits. Most manufacturers offer them. They have one external unit and multiple internal units. The internal units are individually set. The external units usually have one or two speeds so even if most of the internal units are ‘off’ the external unit is still running at the same speed as if all were heating/cooling. One constant is the entire system must be heating OR cooling at the same time, not a mix.
This is not a specific recommendation, just an example of the product type.
As for hydronic systems, there are temperature sensitive valves that can be put on each radiator. A decent HVAC contractor should be happy to visit your premises and offer their suggestions (obviously using their products) so ask a few to come.
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There are numerous larger hydronic system suppliers in Melbourne. Some service more widely.
Note:
The heat pumps required for a hydronic system are designed for that purpose, larger in output and continuous in operation vs a hot water heat pump which has lower output.
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Thank you again, Mark
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You can buy split systems with dual or multi-split inside units. Often this means the outside unit is of a much higher capacity than any of the individual headers that the unit supplies. These days with inverter technology being almost ubiquitous this extra capacity will not be of any or much concern regarding power usage.
A page that has links to a number of units (the business and the units are provided only for information and are not any recommendation)
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Thanks, Grahroll, Good information
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Thanks, Mark
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I know the feeling, but that is just how my stomach functions.
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I think a gastroenterologist might have more success with your gas than I probably will have with mine.
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If your place is large enough you may want to consider a ducted reverse cycle system. They typically have an outlet vent in every room and one return vent somewhere near the middle of the home. Each outlet can be individually turned on and off, though there may be a minimum number which need to be on for the system to work properly.
In any case, you should get an appropriate expert to size the system for you, not amateurs like me! Getting the system correctly sized is vital for an effective solution. Most vendors will do this as part of the quoting process.
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The issue you have in comparing gas vs electric is that gas provides both radiated and convection heat and heat pump relies on convection only. You can still feel warm with a gas fire even if all the air in the room isn’t heated . Depending on your internal wall materials, this can impact energy efficiency too. For example masonry internal walls heat up and retain more heat with radiated heat than convection but no difference with stud walls.
Nevertheless, your suggestion of the 10 kw unit should be able to handle it. But first, you may try to install a ceiling fan that can gently push the heated air from the existing air conditioner that is sitting near the ceiling, down to levels where it can be better felt by the occupants. At the moment , heated air isn’t getting to where it matters and with no radiated heat it feels too cold.
Not every controller supports such individual control, some are zones rather than individual outlet control. We have had both types, I do prefer the individual ones but it is a more expensive build. We have also had multiple splits and they suited the house we had them in over getting ducted.
I think multiple splits have a place in multi room setups. You can get much finer control over a room than if you are using ducted. One room could be heated and another chilled to Antarctic levels 
if each has its own outside unit. Getting the advice of a proper aircon mechanic can help decide the best choices and layouts/placements to ensure the outcome desired.
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Thank you, I have got advice on adding in a 2.2-11.5kW Mitsubishi Split system aircon (MSZ-AS90). Cost of which installed is just over $4,000. I contacted two local companies about heat pumps. The first said the cost would be $15-20,000). Flabbergasted I tried another company. Both supply Hot Water Service Heat Pumps. The second quote was up to $$35,000. I assume that neither wanted to do it. So we are stuck with using gas for the time being, but I probably will move to the Mitsubishi air con in the near future. We do have a very significant central fan to mix the air flows up, but the current Mitsubishi, on its own, doesn’t create enough heat to make a difference.
Perhaps the power supplier might supply reticulated hydrogen in the future, but I am running out of years.s
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