The hidden design decisions behind high-performing underfloor heating systems

Underfloor heating still carries the misconception of being expensive to install and operate. In reality, this is more often as a result of poor decisions being made during design. Pipe spacing, insulation levels, floor construction, glazing performance and heat source selection all influence how efficiently a system performs. It’s why Warm NZ treats the design of each system as the foundation. 

“It’s the one chance you’ve got to get it right,” says Sean. “Good design gives you maximum efficiency, lower running costs and ensures the system performs properly for decades.” 

Through its underfloor heating design service, delivered in partnership with German manufacturer Rehau, Warm NZ develops engineered solutions tailored to the requirements of each project before installation begins. A collaboration that combines more than 75 years of global engineering expertise with Warm NZ’s own 25 years of designing and delivering hydronic heating systems across New Zealand, every design is based on proven engineering principles rather than rule-of-thumb assumptions. Detailed calculations determine everything from heat loads and pipe layouts to zoning and system sizing for homes to large-scale commercial projects. 

The partnership also simplifies long-term ownership. Rather than combining products from multiple suppliers, Warm NZ specifies a fully integrated Rehau system.

“The 25-year warranty covers the underfloor heating, the manifolds and the pre-insulated main right back to the heat source. You’ve got one warranty covering three parts instead of people piecing different bits together and ending up with multiple warranties.”

While Warm NZ can become involved once architectural plans have been completed, the greatest opportunities are possible when heating is considered much earlier in the design process. Engaging with architects and designers from the outset allows the heating system to be integrated into the building, rather than accommodated later.

“It’s easier when we’re involved early on,” Sean explains. “The design system includes the pre-insulated main that runs from the heat source under the slab, so there are stages during construction where we need to be involved. It also gives you better results from your design.”

Rather than positioning a heat pump immediately beside the home, Rehau’s pre-insulated distribution mains allow it to be installed remotely, reducing visual and acoustic impact without compromising performance.

The more information we get, the better the design is.

The design process begins with understanding the building. Floor finishes, room sizes, intended use, slab construction, insulation levels and glazing performance all affect how heat moves through the home. The more information Warm NZ receives, the more accurately the system can be engineered.

“We’ve got to know what the windows are, the glazing and the overall performance of the building,” says Sean. “The more information we get, the better the design is.”

Once plans and project details are received, hydraulic engineers model the system, producing an initial design complete with heat load calculations, pipe layouts and a list of materials. Once the design has been reviewed, a fully engineered package containing commissioning documents and technical calculations suitable for building consent and commercial consultant requirements is provided.

Every step of the process is to achieve a heating system that performs efficiently and economically, and delivers consistent comfort. 

The result is underfloor heating that’s barely noticed. "People think they’re going to have hot floors,” says Sean. “They’re warm, but the whole point is that you don’t really know the heating is on. You’re just comfortable all the time.”

Explore Warm NZ’s underfloor heating design service, product range and completed projects on ArchiPro to see how engineered hydronic heating is helping create healthier, more energy-efficient buildings across New Zealand. Architects, designers and construction professionals can all be found on ArchiPro to collaborate with for your next residential or commercial project.