--- title: "Maximum Demand and Heat Pumps: Designing Big Projects Within Limited Power" date: 2026-09-06T11:00:00+10:00 author: Darren Burch canonical_url: "https://sogeo.com.au/blog/geothermal-heat-pumps-in-melbourne-sydney-reduce-connected-load-and-save-on-electrical-upgrades" section: Pages --- ![Shutterstock 2524287887 1]() # Maximum Demand and Heat Pumps: Designing Big Projects Within Limited Power How a SóGeo geothermal install for a luxury Melbourne home cuts peak electrical demand by 25 to 50 kW, avoids switchboard upgrades and private substations, and heats your pool for free in summer. **The short answer:** maximum demand is the peak electrical load your installation is assessed to draw, and it decides what supply your project needs. Heating and cooling are usually the biggest single contributor. Because a heat pump’s electrical draw equals the heat delivered divided by its COP, a geothermal system running at a COP of 5 to 7 puts far less on the maximum demand calculation than air source equipment or electric resistance, and that difference often decides whether a project fits its existing supply. **Try it yourself:** our free [Maximum Demand Calculator](/tools/maximum-demand-calculator) applies the AS/NZS 3000 Appendix C method and shows, line by line, how the choice of heating and hot water plant changes the number. ## What Is Maximum Demand? Maximum demand is the realistic peak load of an electrical installation, calculated by your electrician under AS/NZS 3000 using the assessment methods in Appendix C. Rather than adding up every appliance at full power, the standard applies demand factors to each load group: lighting counts at a reduced rate, socket outlets are grouped, cooking appliances count at half their connected load, and fixed space heating or air conditioning is counted at 75 percent of its full load current. The result determines the size of your consumer mains, your switchboard, and whether the network needs to offer you more supply. On a renovation or a large new home, a high maximum demand is what triggers the expensive conversations: a switchboard upgrade, a three phase supply application, or on large projects a substation contribution. ## Why Heating Drives the Number Go down the load groups on a maximum demand calculation for a substantial home and one line dominates: space conditioning. A big home in Melbourne can need 30 to 40kW of heat on a winter design day. Deliver that with electric resistance and you are adding 30 to 40kW of electrical load. Deliver it with air source heat pumps and you are adding the thermal load divided by whatever COP the equipment achieves at winter design conditions. Deliver it with geothermal and you divide by a COP of 5 to 7 that does not degrade with the weather, because the ground it draws from holds a stable temperature all year. ## How Much Power Does a Heat Pump Actually Draw? The arithmetic is simple: peak electrical draw is the heat delivered divided by the COP. A typical home needing 10 to 15kW of heat draws roughly 2 to 3kW of electricity through a geothermal heat pump holding a COP of 5 to 7. A large luxury home needing 40kW of heat draws proportionally more, roughly 6 to 8kW. Deliver that same 40kW with air source equipment at winter design conditions and the draw can run around 40 percent higher, and on a maximum demand calculation that difference is often exactly what decides whether the project fits the existing supply or pays for a switchboard, three phase or substation upgrade. 01 ![Pump room 3]() ### Geothermal vs Air Source at Design Conditions The gap widens exactly when it matters most. A maximum demand assessment cares about the worst case, and the worst case is a design-condition day. Ground temperature a few metres down barely moves between January and July, so a geothermal heat pump delivers its COP of 5 to 7 on the coldest morning of the year and holds efficiency through a heatwave, where summer cooling is concerned, when air source cooling performance falls as the air gets hotter. Air source equipment earns a strong SCOP across a season, but at the design extremes that maximum demand is assessed against, its draw climbs. If the electrical case for your project is tight, the stable machine wins the calculation. ## What This Means for Your Project For architects, builders and owners of larger homes, the practical value is straightforward: geothermal shrinks the heating line of the maximum demand calculation to the point where projects that looked like they needed a supply upgrade often do not. We have designed systems for luxury homes and estates where the entire heating and cooling plant draws less than a single ducted air conditioning system would have, keeping the project inside its existing supply and putting the upgrade money into the home instead. The same logic scales to multi residence and commercial projects, covered on our [commercial hydronic systems](https://sogeo.com.au/commercial-multi-residential-hydronic-heat-pump-systems) page. ## A Worked Example Take a 500 square metre home with a calculated heat loss of 40kW on a Melbourne winter design day. As electric resistance, heating adds 40kW to the load groups. As air source heat pumps at design conditions, roughly 10 to 11kW. As a geothermal system at a COP of 5 to 7, roughly 6 to 8kW. Whether each of those fits the existing supply is precisely what the maximum demand calculation determines, but the ranking never changes: the geothermal number is the smallest, by a margin that frequently equals the entire cost of an electrical upgrade. For how the system itself works, see our [ground source heat pumps](https://sogeo.com.au/ground-source-heat-pumps) page. ## Common Questions ### How do you calculate maximum demand? Your electrician calculates it under AS/NZS 3000 Appendix C, applying demand factors to each load group: lighting, socket outlets, cooking, fixed space heating and cooling at 75 percent of full load current, water heating and other fixed appliances. For a quick estimate before your electrician runs the formal calculation, use our [free maximum demand calculator](/tools/maximum-demand-calculator). For most homes the calculation method in Table C2 applies, and for larger or unusual installations the assessment can be done by calculation or measurement. ### Does a heat pump need three phase power? Often not. A typical residential hydronic heat pump drawing 2 to 3kW runs comfortably on single phase. Larger systems and cascades may be specified as three phase units, and the right answer comes out of the heat loss calculation and the maximum demand assessment together, which is exactly the design work SóGeo does before quoting. ### How much does a heat pump add to maximum demand? Divide the heat you need by the COP of the machine delivering it. Through a geothermal heat pump at a COP of 5 to 7, a 15kW heating load adds roughly 2 to 3kW of electrical demand. The same load through equipment with a lower design-condition COP adds proportionally more, which is why the choice of heat source belongs in the electrical design conversation from day one. 01 ![SoGeo Team At Work]() ### The Geothermal Advantage Geothermal heat pumps, also known as ground source systems, use stable underground temperatures for efficient heat exchange. The result is: - **COP of 5 to 7** far higher than traditional air-based systems - **50 to 70% lower energy usage** for heating and cooling - **Significantly reduced peak electrical draw** Because they operate steadily and don’t rely on backup elements, geothermal systems help keep your **connected load low and predictable**. This avoids those demand spikes that cause distributor headaches. ### Freeing Up Power for What Matters With less of your site’s electrical capacity going to HVAC, you can preserve it for: - **EV chargers** (7 to 11 kW) - **Extensive wine cooling system** - **Home automation, lighting, and cinemas** Geothermal gives your clients all the luxury, without the electrical upgrade. --- ### Speak with SóGeo If you’re an architect or builder working on a project where power capacity is tight, geothermal could be the key to keeping things moving , and keeping the home high-capacity without compromise. 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