Replacing ducted gas heating with reverse-cycle: the honest cost-benefit
Most homes save $1,400+ a year. But not all of them. Here's how to work out if your house is one of the winners.
Ducted gas is heading the way of open fireplaces. Gas prices in Victoria are up 30% over five years and heading further. Reverse-cycle ducted (aka "ducted heat pump") is the modern replacement, same ductwork, better efficiency, cooling in summer too. But it doesn't make sense for every house. Here's the honest maths.
How reverse-cycle saves you money
A ducted gas heater runs at about 70-85% efficiency, for every $1 of gas you burn, 70-85 cents ends up as heat in the house. A modern inverter reverse-cycle system runs at a coefficient of performance (COP) of 3-4, for every $1 of electricity, you get $3-4 of heat out. That's a 4-5x efficiency gain.
Combined with dropping electricity prices as solar kicks in and rising gas prices, the running-cost gap is now huge. A typical Pakenham 4-bedroom home uses about 25,000 MJ of gas a winter for heating, that's around $1,650 at 6.6 c/MJ. The same house running an 18 kW reverse-cycle would use about 3,500 kWh of electricity, about $700-900 at current rates, or $200-300 if you've got solar.
So you're saving $750-$1,450 a year on running cost. Plus you get cooling for summer as part of the deal.
When it doesn't stack up
You've got single-phase power in a big house. Anything over 18 kW ducted needs 3-phase, if you're stuck on single-phase you're capped at ~18 kW capacity, which handles a 4-bedroom home comfortably but might not stretch to 5-6 bedroom homes.
Your ductwork is unusable. If the existing ducts are galvanised (30+ years old), flexible ducting with tears, or wildly wrong-sized for reverse-cycle airflow, we need to replace them. Adds $2,000-4,000 to the job.
You have no gas bill above ~$1,800/year for heating. Below that, the payback stretches to 8-10 years and you might be better waiting for the next generation of ducted heat pumps.
Real numbers
An 18 kW Mitsubishi Electric ducted with Milieu Lab controller and up to 12 zones: from $11,000 fully installed after VEU rebates. Big number, but the running-cost savings mean it pays back in 6-8 years and you get 15-20 years out of the equipment.
Kaden and Rinnai equivalents come in $1,500-2,500 cheaper for similar capacity, worth considering if you're budget-constrained.
We do a full roof-cavity survey before quoting, no surprises on the day. Book a site check and we'll price it properly.
Fixed-price, no obligation, VEU rebate applied at the quote.
We usually reply within 12 hours. Free 20-minute site check for bigger jobs.
