Heat Pump vs Gas Hot Water Australia: Cost, Rebate & Verdict (2026)

Published 15 May 2026 · By Plumberthon, licensed Sutherland Shire plumber

Your old hot water system has died — or is about to. You've got two real options for replacement in 2026: a heat pump or a gas instantaneous unit. Both are good. They suit different houses. We install both, we have no skin in the game either way, and we'll tell you straight what we'd put in our own homes.

This guide is the conversation we'd have with you on-site. Skip to the verdict at the bottom if you only want the answer.

Quick answer

If you already have mains gas at the house and your hot water usage is average for a family of 4 — gas instantaneous is cheaper upfront, easier to install, and the running cost difference vs heat pump is smaller than the rebates make it look.

If you don't have gas, or you want the lowest running cost over 10 years, or you'll be in this house long enough to claim the payback — heat pump wins, especially in NSW where the federal STC rebate + NSW Energy Savings Scheme rebate stack to $1,300–$2,500 off the sticker price.

The boring answer is "it depends." The honest answer is below.

The two systems in 30 seconds

Gas instantaneous (continuous flow)

A wall-mounted unit that fires gas to heat water on demand. No storage tank, so it never runs out of hot water and there's no standby heat loss. Compact, runs forever as long as gas flows. Brands: Rinnai, Bosch, Rheem. Sticker price installed: $2,200–$3,500.

Heat pump

An electric system that uses a small refrigerant compressor (like a reverse-cycle AC, but for water) to extract heat from outdoor air and transfer it to a storage tank. About 3–4× more efficient than a resistive electric element because it's moving heat, not making it. Brands: Sanden Eco, Reclaim Energy, Aquatech, iStore. Sticker price installed before rebates: $4,500–$5,500. After NSW rebates: typically $3,000–$4,500.

Side-by-side comparison

	Gas instantaneous	Heat pump
Upfront installed	$2,200–$3,500	$3,000–$4,500 (after rebates)
Running cost (family of 4)	~$700–$900/yr	~$300–$500/yr
10-year running cost	~$8,000	~$4,000
Lifespan	10–15 years	10–15 years (compressor)
Hot water capacity	Endless	200L–315L stored, refills overnight
Space needed	Wall-mounted, small	Outdoor compressor + tank, fridge-sized
Annual service	Required for warranty	Not required, but recommended
Carbon footprint	~700kg CO₂/yr	~250kg CO₂/yr (less if you have solar)
Best paired with	Existing mains gas + small lots	Solar PV + grid electricity + room for outdoor unit

The rebate stack you might not know about

Heat pump conversions in NSW qualify for three separate rebates that stack. Most plumbers we've seen will only mention the federal one (the STC rebate). We hand off the others as well — they come off your invoice on the day, not as a refund you chase later.

1. Federal STC scheme (Small-scale Technology Certificates)

Created under the federal Renewable Energy Target. Each heat pump install generates a number of STCs based on system size and your climate zone (Sydney is Zone 4 for solar/HP rebates). Spot price ~$39 per STC in 2026.

Typical Sydney heat pump STC value: $800–$1,200 off the install. Applied at point of sale — you pay the discounted price, the installer claims the STCs from the Clean Energy Regulator.

2. NSW Energy Savings Scheme (ESS) — Energy Savings Certificates

Administered by IPART. Pays installers ESCs per MWh of energy saved by upgrading from electric resistive to heat pump (or from gas to heat pump in some cases). Trades ~$17–$26 per ESC. A typical heat pump install generates 25–40 ESCs.

Typical NSW ESS value: $400–$1,000+ off the install. Only available through an Accredited Certificate Provider (ACP) — we sub-contract under an ACP for our heat pump installs so this rebate flows to your invoice.

3. NSW Peak Demand Reduction Scheme (PDRS)

Smaller add-on rebate for cutting peak afternoon electricity demand (2:30pm–8:30pm, summer months). Heat pumps qualify because they typically heat overnight on off-peak power, not at peak time.

Typical PDRS value: $100–$300. Stacks with ESS through the same ACP paperwork.

Combined

NSW heat pump customers can see $1,300–$2,500 off the sticker when all three rebates are applied. This is why "after rebates" pricing on a heat pump is so much lower than the catalog price you'd see at Bunnings.

Where each option wins

Gas instantaneous wins when:

• You already have mains gas at the house and a working gas line to the existing HW unit
• You have small to medium hot water demand (1–4 people, ordinary usage)
• You have limited outdoor space (no room for a heat pump's outdoor compressor unit)
• You don't want to deal with a bigger system or rebate paperwork
• You'll be in the property less than 5 years (you won't recoup the heat pump premium)
• You don't currently have solar PV (heat pumps work brilliantly with solar — gas does not)

Heat pump wins when:

• You don't have mains gas (or your gas line is rusted out and needs replacing anyway)
• You have higher hot water demand (4+ people, teenagers, pool) — but choose a 270L+ tank model
• You have solar PV — running the heat pump on excess daytime solar makes effective hot water cost ~$0
• You'll be in the property 5+ years
• You want the lowest carbon footprint or you're on a sustainability kick
• You have outdoor space for the compressor unit (typically 600×400×400mm) close to the tank location

Common mistakes we see

1. Sizing the heat pump wrong. The 170L base models are for couples, not families. A family of 4 needs 270L. A family of 5–6 with teenagers needs 315L. Under-sizing means morning showers run cold on the third user.
2. Putting the heat pump compressor in a bad spot. They need airflow on the back and sides. Wedging one against a fence or in a cupboard kills efficiency and shortens compressor life. Worth a quick site assessment before ordering.
3. Buying a heat pump online and asking a plumber to "just install it." This usually forfeits the STC + ESS rebates because the installer has to lodge them and won't do that for a unit they didn't supply. You pay sticker price ($4,500–$5,500) instead of post-rebate price ($3,000–$4,500). Net loss: $1,000–$1,500.
4. Ignoring the gas service requirement. Gas instantaneous units typically need an annual service to maintain the manufacturer warranty. $180–$280 per year. Not optional if you want to claim a warranty fault later.
5. Heat pump with no solar. Still better running cost than gas, but the "near-zero hot water cost" headline only happens when you have solar PV producing during the heat pump's heating cycle. Without solar, heat pump runs on grid power and saves you ~$400/year vs gas, not the $700+ you might read about online.

Lifespan and reliability

Both systems realistically last 10–15 years with good maintenance.

Gas instantaneous failures: usually the heat exchanger or the gas valve, which is repairable for $300–$600. Annual service catches problems early. The unit is wall-mounted and accessible, which keeps repair costs reasonable.

Heat pump failures: usually the compressor (the expensive bit) or the refrigerant circuit. If the compressor goes, you're often better off replacing the whole unit rather than repairing — compressor swap-outs run $1,500+ in labour and parts. Tank itself usually outlasts the compressor by years.

The under-the-counter truth: gas instantaneous is more repairable, heat pumps are more "replace when broken." Both are reliable enough that it shouldn't be the deciding factor for most homeowners.

What we'd put in our own house

Honestly? Depends on which house. If we had solar PV and outdoor space, heat pump every day. If we were in a small inner-city terrace on mains gas, gas instantaneous. The stacked NSW rebates make heat pump significantly cheaper than people realise — but they don't help if you don't have grid electricity (and not gas) or no space for the outdoor unit.

The right call is the one that fits your house and your usage. We'll quote both options on-site and you choose based on actual numbers, not catalog marketing.

Get a fixed-price quote on either option

We install both gas instantaneous and heat pump systems across the Sutherland Shire from our Caringbah base. Fixed-price quote on-site, all rebates applied to your invoice, removal of old unit included.

Related

• Hot Water Plumber Sutherland Shire — full pricing table + service details
• Gas Fitter Sutherland Shire — gas fitting, compliance certificates, BBQ lines
• 24/7 Emergency Plumber — when your hot water dies at 6am on a Sunday