--- title: "Main Ridge: A Lake-Source Geothermal Heat Pump for Existing Underfloor Heating, SCOP 5.1" date: 2025-02-12T15:25:00+11:00 author: Darren Burch canonical_url: "https://sogeo.com.au/case-studies/case-study-exploiting-lake-energy-for-efficient-heating-in-main-ridge" section: Pages --- ![Stiebel Eltron Geothermal Hydronic Heat Pump By SoGeo]() # Main Ridge: A Lake-Source Geothermal Heat Pump for Existing Underfloor Heating, SCOP 5.1 Grant’s Main Ridge home already had hydronic underfloor heating. A 15 kW Stiebel Eltron heat pump drawing on the property’s spring-fed lake replaced the old plant with no drilling, a one-week install and a measured SCOP of 5.1, despite a demanding 50 to 55°C flow temperature. **Location**Main Ridge, Victoria**Project**Heat source upgrade to an existing hydronic underfloor heating system**Heat source**Spring-fed lake on the property, holding around 8°C through winter**Heat pump**15 kW Stiebel Eltron geothermal heat pump on a lake loop**Plant room**Custom wall-mounted buffer tank; fixed-speed circulation pumps replaced with EC units**Installation**One week, delivered entirely by the SóGeo team**Measured result**SCOP 5.1 at a flow temperature of 50 to 55°C## The brief Grant engaged SóGeo to upgrade the heating on his Main Ridge property. The home already had hydronic underfloor heating, so the distribution was in place. The job was to lift the efficiency of the heat source, and the site offered a resource the existing plant had been ignoring: a spring-fed lake. ## The challenge The plant room was small and packed with outdated, energy-hungry fixed-speed pumps, with no floor space to spare for the buffer tank a heat pump system wants. And the existing underfloor circuit was laid at a 200 to 250 mm pipe pitch in the concrete slab, which meant it needed a flow temperature of 50 to 55°C to meet the home’s heat loss. That is a higher lift than a typical underfloor design, and it set the ceiling on the efficiency any heat pump could reach here. 01 ![Stiebel Eltron Geothermal Hydronic Heat Pump By SoGeo]() ### The system A lake loop instead of boreholes, a buffer tank on the wall instead of the floor, and pumps that modulate with the heat pump. We installed a 15 kW Stiebel Eltron geothermal heat pump drawing on the lake as its heat source, a project also featured on the Stiebel Eltron project showcase. A closed lake loop exchanges heat with a body of water that sits at a stable, mild temperature all year, around 8°C in winter, and it did so at a fraction of the installation cost of a vertical borehole geo-exchange, with no drilling on the property at all. In the plant room we specified a custom wall-mounted buffer tank from Germany, which used wall area that a floor-standing tank could not and freed the limited floor space. The old fixed-speed underfloor circulation pumps were replaced with modern EC (electronically commutated) units: higher efficiency, finer control, and the ability to modulate alongside the heat pump’s variable output. The full installation was completed by the SóGeo team in one week, with no external contractors. ## The results The system achieved a seasonal coefficient of performance (SCOP) of 5.1: across the season it delivered 5.1 units of heat for every unit of electricity it used, measured from the system in operation rather than read from a datasheet. That is a strong result given the design conditions. The lake source averages around 8°C in winter, and the existing slab pipework demanded a 50 to 55°C flow temperature, a high lift for any heat pump. The stability of the lake source is what kept the efficiency strong despite it; the same heat pump on a new underfloor circuit at closer pipe spacing and a 35°C flow would climb well above 5. Grant reports a measurable reduction in electricity bills and even, predictable heating across the home. ## What made it work - **Using the resource on site.** Where a property has a suitable body of water at a stable temperature, a lake loop is a viable, lower-cost alternative to drilling, and it delivers the same stable-source advantage that makes geothermal efficient. - **Solving the plant room instead of compromising the system.** A wall-mounted buffer tank resolved a space constraint that would otherwise have forced a smaller, worse-performing design. - **Pumps that speak the heat pump’s language.** Replacing fixed-speed circulators with EC units lifts efficiency and gives the heat pump’s variable output a matching instrument on the load side. - **Honesty about flow temperature.** Emitter design sets the ceiling on SCOP. This project shows what a stable source achieves even at 50 to 55°C; a low-temperature emitter is how the same plant reaches the high sevens and eights on our other projects. ## Related Loop options, including lake and dam loops: [geothermal heating and cooling systems in Australia](/blog/geothermal-heating-and-cooling-systems-australia-guide). The technology: [ground source heat pumps](/ground-source-heat-pumps). The distribution: [hydronic underfloor heating](/hydronic-heating-cooling/hydronic-underfloor-heating-comfort-efficiency). More projects: [SóGeo case studies](/case-studies). *Have an existing hydronic system and a dam, lake or generous block? [Ask SóGeo what your site can do](/contact-us).* ## Our Partners [ ![Reece](https://sogeo.com.au/uploads/suppliers/_AUTOx96_crop_center-center_none_ns/Reece.png) ](https://www.reece.com.au/) [ ![Stiebel Eltron](https://sogeo.com.au/uploads/suppliers/_AUTOx96_crop_center-center_none_ns/Stiebel-Eltron.png) ](https://www.stiebel-eltron.com.au/) [ ![Mitsubishi](https://sogeo.com.au/uploads/suppliers/_AUTOx96_crop_center-center_none_ns/Mitsubishi.png) ](https://www.mitsubishielectric.com.au/) [ ![Purmo](https://sogeo.com.au/uploads/suppliers/_AUTOx96_crop_center-center_none_ns/Purmo.png) ](https://www.purmo.com/au) [ ![Viessmann](https://sogeo.com.au/uploads/suppliers/_AUTOx96_crop_center-center_none_ns/viessmann_wordmark_rgb_1_vitorange.png) ](https://www.viessmann.com.au/)