Knowledge/Systems/Hydronic heating, and what the rental rule does to it
Hydronic heating, and what the rental rule does to it
Water carries the heat, from a gas boiler or an air to water heat pump. A heat pump typically gives 3.0 to 5.0 units of heat per unit of electricity, its coefficient of performance (COP). Owner occupiers can swap a gas boiler like for like. From 1 March 2027, a failed heater in a rental points to reverse cycle.
- Heat pump COP
- 3.0 to 5.0air to water, typical range
- Owner occupier
- No requirementto move off gas space heating
- Rental, on failure
- 1 Mar 2027reverse cycle air con (RCAC), main living area
- Response time
- Slowpoor fit for a house that sits empty a lot
How it works, and the comfort argument
Water carries the heat around the house. It's heated by a gas boiler or by an air to water heat pump, typically with a COP of 3.0 to 5.0. Gas boilers are on the way out in rentals and new homes, but an owner occupier can still replace one like for like. The heat comes out through panel radiators, pipes in the floor or slab, or trench convectors.
The comfort is the selling point. It gives steady radiant warmth instead of blowing air around, so the air doesn't dry out and dust isn't stirred up. That's the standard Victorian pitch against ducted and it's a fair one.
The catch is it's slow to warm up. In slab heating in particular doesn't suit a house that's only lived in now and then. A holiday house on in slab hydronic is a bad match, and it's worth saying so before you quote it.
The rental rule, and why it matters most here
Gas hydronic is treated the same as gas ducted and gas wall furnaces. Because there's no requirement to upgrade gas space heating, an owner occupier can keep swapping the boiler like for like, with no end date.
Rentals are different. From 1 March 2027, where a heating appliance breaks and can't be repaired, it has to be replaced with an efficient electric reverse cycle air conditioner in the main living area.
Read that carefully, because the wording does something people don't expect. As the government words it, the rental rule names RCAC specifically, not electric heating generally. So a landlord with failed gas hydronic is pointed at reverse cycle, not at an air to water heat pump fitted to the radiators already there.
Check it against the final regulations and the exemptions list before you advise anybody, because it's the kind of detail that gets refined.
Left out on purpose
What we couldn't source for hydronic
Hydronic is the lightest coverage in this library, and we'd rather say so than pad it out. We couldn't find a source for flow and return temperatures for radiators versus in slab, a radiator sizing method, buffer tank requirements, or Victorian install costs.
One more is widely understood but unsourced. Heat pumps need low temperature emitters - radiators or floors that work at lower water temperatures. So fitting a heat pump to radiators sized for 70 to 80°C boiler water usually means bigger radiators. That's the accepted engineering position, but we haven't found an Australian citation for it. Treat it as a design question for your supplier, not a figure off this page.
Weighing up what to put in front of a customer?
Most of the hard calls aren't technical. They're about what you can stand behind when the customer rings you in February.
Kevin's been having that conversation for thirty years. Ask him.
Who this is for: small and medium HVAC contractors in Victoria. If you're a homeowner after a rebate or a repair, you need a licensed contractor, not us, and yours can point you the right way.
Related
- Does a Victorian gas heater have to be replaced with electric?If the owner lives there, a dead gas ducted heater doesn't have to go electric. Space heating was dropped from the rules. Rentals are different from 2027.
- How evaporative cooling actually worksThe gap between dry bulb and wet bulb sets how cold it can get. Efficiency decides how much of that you get. Humidity limits every brand the same way.
- Sizing an evaporative cooler on air changes per hour20 to 40 air changes an hour is the engineering range and 30 is the trade shortcut. Both are sourced. Then the 80 Pa check that decides your outlet count.
- How an indirect gas ducted heater worksIndirect means the flue gases never mix with the air you breathe. How it holds outlet temperature, what shuts it down, and the gas pressures it needs.
Review date: 1 March 2027. Figures in this area change without much notice and this page carries some that will go stale. Every number above is dated and sourced so you can check it yourself. If you find something out of date here, tell us and we will fix it.