Can any one tell me with authority which is cheaper to run ducted gas or reverse cycle air-conditioning to heat my home in this bitter cold Melbourne winter.
My house is of open plan design and my last gas bill was $1250 ! !
I have both ducted gas heating and a large reverse cycle air conditioner.
I have always understood that gas ducted heating was the cheapest but i have seen article suggesting reverse cycle air-conditioning is now cheaper but there article were by those having a vested interest in selling air conditioners
For a simple estimate note 1kWh of thermal energy corresponds to 3.6MJ. Your gas bill will have an energy value measured in MJ for the period. If you also use gas for hot water and or cooking a bill from summer without heating can provide an estimate for that portion of your consumption and estimate how much gas is used for heating.
To estimate the electricity needed to deliver a similar amount of heating with split systems it’s two simple calculations.
First divide the estimated gas usage that is in MJ by 3.6 to convert to kWh.
Second step divide the thermal energy in kWh by the COP of the split system. Typically 3.5 up to 4.5. I’d use an average of 4.0 based on common MHI products.
Assuming your usage for the gas bill after deducting an allowance for cooking/hot water is 30,000MJ
30,000 MJ / 3.6 = 8,333 kWh heat energy
8,333 kWh / 4.0 = 2,083 kWh electrical energy consumption estimate.
Looking to your electricity provider and tariffs will enable an approximate cost comparison.
Note there are other factors to consider. Several to note:
A ducted gas heating system will have some losses and not quite deliver 100% of the heat (thermal energy) paid for.
Electricity distributors have committed to moving customers to cost reflective tariffs, EG ToU (time of use). Costs for energy used during the evening peak period will increase relative to a existing averaged flat tariffs.
Solar PV can provide some of the power required to run RC split systems. Less so in winter.
Looking to gas and electricity prices I’ve paid in Brisbane. The energy cost for gas or an electric split system for heating appear to slightly favour split systems. Of course split systems also offer efficient cooling in summer, which gas cannot.
It is unclear if the question is about ducted reverse cycle (whole of house or zoned) A/C systems or split systems. The perceived comfort provided by hydronic (regardless if fired by gas or heat pump) [heat] vs a ducted A/C system vs ducted gas [heat] vs individual split A/C systems will generally be noticeably different. When the cost of installation or change is included it could be pocket change or many years for economic break even – unless reducing energy is the only criteria, a valid goal.
Agree, there are other considerations beyond the OP’s opening question.
On the relative differences in consumption of energy (note I’ve added a heading to my reply to better define the context), being able to convert between electrical and gas energy is useful. The total costs (fixed and variable/supply) of the different options are also important, and not so readily assessed.
There is an assumption that @pubtest as an owner of both a large RC aircon and gas heating system is familiar with differences in comfort etc… Which best suits an individual need and how to get the benefits of the alternatives as you point out are additional considerations.
Victoria has a well established NG supply network, and a large market share with established home users. NG until recent years has been heavily promoted and provided at a low cost relative to electricity. Doubtless a topic of discussion with family when in Melbourne enjoying the best August has to offer.
I suggest you contact a qualified HVAC engineer, not a salesperson, to inventory the characteristics of your house, your ducted gas and your reverse cycle A/C, and advise you accordingly. A good report will include ranges of gas/electric costs that will influence which is cheaper to run under what ranges, and if you have a PV system with or without batteries, how much that could influence the equation. Some HVAC companies will have engineers and sales engineers on staff; others will just have salespeople.
As a general statement electric reverse cycle inverter systems should be cheaper to operate than gas. Can an armchair observer without ‘the details’ quantify how much? I doubt it but maybe there will be a surprise contribution?
Unfortunately the Choice article skirts around ducted systems but some of the commentary might be instructive.
All that I can take way from the advices given is that it is not clear cut,and that there is no clear difference in running costs.
As I state in my question I recall the time when it WAS clear cut in that ducted gas heating was the way to go and substantially cheaper to run than electricity…but it appears from what has been written such is no longer the case !
Possibly why when one is considering major expenditure on home heating etc, the advice to seek out a HVAC specialist Engineer as @PhilT mentioned is pertinent. There are so many factors in addition to the daily cost of energy, from which ever source it comes. And that appears to be changing on a daily basis whether NG, Grid electricity, or petroleum products.
Australia not including WA made a decision to become the world’s largest exporter of LNG. Enough said about the cost of domestic supply. There has been plenty of heated (no pun intended) finger pointing in full public view over prior months.
It is difficult to be certain when comparing gas versus electricity costs because there are so many variations in personal circumstances. For example, I have a ducted gas heater that heats the whole house. I also have a reverse-cycle air-conditioner (RCAC) that heats/cools one room. Solar panels are on the roof. If I stop using gas for heating, to cut costs, then I would need to install either a central ducted RCAC or several RCAC units to heat the whole house. The increased capital cost would be high to, perhaps, reduce the running costs. So this presents a dilemma. I’ll stick with gas until the position becomes clearer.
Compare the Market advise that heating by a reverse cycle AC is probably more efficient at heating than gas. That would likely mean in your case a modern AC unit will be more cost effective.
“ Gas is less powerful than electricity. This means you need to consume more gas to reach the same output of electricity”
“Some modern electric appliances, like split-system heating, are actually more efficient and cheaper to run than most gas systems“
Hope that helps answer your question, however you should read the article as it does explain it in more detail. We are generally not experts in home heating or cooling, we answer as best we can in only general terms. You, if needing more definitive answers, are better advised to seek the opinions of qualified tradespersons who work in the area of home heating and cooling than relying on our opinions.
Same for us in that there is a substantial investment required to converting from gas. The least impact financially will be when the gas appliances require replacement. We use a modest 5000-6000 MJ (LPG) annually between 2 people. There is no use for heating as we have RC split systems and a small hydronic system. Any difference in running costs between gas and electric is not significant enough to justify the change.
Relative to personal carbon footprints, we can make a greater positive impact with similar expenditure on other needs.
The Victorian Govt initiative to subsidise Heat Pump HWS upgrades shows what can be done. Not available for us.
It’s a small consolation that when using gas for the oven and cooking in the evenings, we are not adding to the peak electricity demand on the NEG. Typically that demand here is met through natural gas peaking generators. The losses in generation and transmission are approx 3 fold those used more directly in the kitchen.
Oh dear, hopefully the edit has sorted that one.
Which should make sense of the following, if not it’s intended to say ‘electricity demand’.
Energy lost in generating electricity with gas!
Burning gas in a turbine for electricity generation is 20-35% efficient. I’ve referenced a US source as there are many different efficiencies on the web, subject to which point is up for discussion. There are further small losses electrically in transmission and distribution. Electric cooktops are more energy efficient compared to gas, but only based on the energy input directly at the cooktop or oven.
For those cooking in the evening and using electricity in peak times, if your electricity comes from a ‘peaking’ (outwitted Apple that time) GT generator your electric cooktop could be using approx 3-5 times the gas for the evening meal compared to a gas cooktop. I could have suggested an average of around 4 times, however gas cooking does waste more heat than electric, hence 3 times. The relative difference comparison varies with type of electric cook top and type of electric oven.
There are a number of different ways to look at how imperative it is to eliminate gas from residential consumption when there is significant consumption of gas in electricity generation. The most expensive electricity to supply is that for the evening ‘peak demand’ period due mainly to the use of gas to supply that peak. It’s a ‘chicken and the egg’ like situation. Burn less gas at home by electrifying, increase peak demand for electricity in the evenings and burn more gas at the power station. Potentially more than some of the gas displaced from home use. It suggests if there is a priority for displacing gas from consumers homes it first needs assurances to supply sufficient low cost electricity in the evenings. Something gas generation is not the best solution to.
It may go part way to explain why some consumers keen to transition to all electric are hanging on to gas. Electricity is only cheap off peak, for now. There is also a degree of independence and security in not being totally reliant on the grid. More a feel good than essential, but often raised by those who have the option.
The linked article provides a good comparison: https://www.solarquotes.com.au/blog/air-conditioners-vs-gas-heating/ Note that a reverse cycle aircon delivers kW of heating at 3 to 5 times the kW of electricity it uses. This ratio (AKA Coefficient of Performance - COP) depends on the efficiency of the aircon system (e.g. star rating) and the outside air temp it’s working in (it heats less efficiently as it gets colder outside). A cost comparison also depends on the prices paid for gas and electricity.
Few comparisons and advisories appear to explicitly include ducted systems for either heating or cooling (and only very rarely reference hydronics for heating). Unless I missed it, both the Choice article as well as the linked solarquotes comparison seem to use an ‘old school’ gas [wall] heater of some sort as the gas heating reference.
As electricity is following gas pricing as well as considerations of climate change, particular products in particular settings with forecast fuel costs really require differential equations to know which is probably best, noting fuel costs can be as speculative over time as rainfall in any given period.
Just pointing out one size does not fit all, nor usually any particular case outside that specified.
FWIW my hydronic boiler can theoretically achieve >91% efficiency. The losses in the hydronic distribution system? Priceless. That being written the linked article is quite good when read in its entirety, as is most everything on solarquotes.
Irrespective of the relative costs, fossil fuels still deliver the majority of our electricity. In particular in the evening when heating and cooking demands peak. The efficiency of our existing FF coal and gas fired generators 35-45%. It’s not considered in the article graphics. It is discussed separately in the linked article. (edit)
Why would it be? These graphs are about cost to the consumer. When buying gas for home heating the efficiency of the burner matters as you buy before burning. When buying electricity the conversion losses of burning gas or coal are already factored into the price. There are losses too due to transmission of electricity or leakage of gas but they are both before it arrives to be metered at the house.