Hi @Gas2,
Welcome to Neighbourhood! Generally speaking customers who have ducted gas heating find they have high increase of usage over winter months.
Your hot water system will use more gas over winter as well, in saying that, on it's own you wouldn't see a high increase due to hot water system alone.
You can work out how much your ducted gas heating is using on your normal setting. Take a photo of your meter, run your heating for an hour, take a photo of your meter again. The difference of the 2 reads is your usage. To convert this to mj, you would multiply this by Heating Value and then by Pressure Factor as displayed on your latest bill.
We can certainly help you work this out, if you're not sure how to calculate this.
Kind Regards,
Olgi
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