The search “heat pump STC deeming 10 years” comes from a real number that is easy to misread. Here is what the 10 refers to and why the rebate still shrinks.
Where the 10 comes from
The Clean Energy Regulator’s register of solar water heaters lists how many STCs a model is eligible for based on the life of the system, and the register states that life is currently set at 10 years. That is the basis for the model’s entitlement. It is not a promise that a heat pump will always create 10 years’ worth of certificates.
What happens each year
The regulator’s calculation method multiplies by a factor that follows the deeming period for the installation year. The deeming period steps down one year each January, and the factor falls by 0.1:
| Install year | Deeming period | Factor |
|---|---|---|
| 2026 | 5 years | 0.5 |
| 2027 | 4 years | 0.4 |
| 2028 | 3 years | 0.3 |
| 2029 | 2 years | 0.2 |
| 2030 | 1 year | 0.1 |
The scheme ends on 31 December 2030, so there is no 2031 column.
Do heat pump STCs decrease each year?
Yes. Moving from 0.5 to 0.4 removes a fifth of the count on 1 January 2027, then a quarter of the 2027 figure in 2028, and so on. Illustratively, a unit that creates 25 STCs on a 2026 install would create about 20 in 2027, 15 in 2028, 10 in 2029 and 5 in 2030. Real counts come from the register for your model, zone and date. At roughly $38 to $40 per STC at the time of writing, that unit’s discount drops by roughly $190 to $200 each year.
Solar hot water deeming in 2026
Solar water heaters use the same schedule as heat pumps, so a 2026 install has a 5-year deeming period and a factor of 0.5. The difference is the zones: solar water heaters use four postcode zones and heat pumps use five. See solar hot water STCs by tank size and zone.
How it differs from solar panels
Rooftop solar has the same deeming period schedule but uses a different calculation: kilowatts, times the zone rating, times the number of years. Hot water uses the register’s per-model figure and a factor. The direction is the same: smaller every year. The solar version is in STC deeming period by year.
Timing a purchase
Because the install date decides the count, a heat pump booked for late December earns more than one booked for early January. If you have a need for hot water now, do not wait for a price drop: the hardware rarely falls fast enough to offset a one-fifth cut in the discount. If your old system is working, the saving from waiting is real, and it is a judgement call.
What this means for you
Homeowners should ask for the install date in writing and treat 31 December 2026 as a real cut-off. Installers should lodge claims with the right install date and zone, and see the hot water STCs pillar and the hot water checklist. For rates, see pricing, and for the broader 2027 picture, STC deeming period 2027: what changes in January.