Case Study from: Grant Store Ltd.
Learn how Grant Store sized a UK bungalow’s heat pump system accurately with h2x.
Name: Deane Ashcroft
Role: Company Director
Company: Grant Store Ltd.
Location: Lancashire, England
Architecture: 35 The Studio Ltd.
The Background
Grant Store Ltd. were took on to deliver a full heating and plumbing re-fit for a renovated four-bed bungalow in Lancashire, UK. The brief covered two bathrooms, a kitchen, and utility, with the entire property heated via underfloor space heating served by two manifolds and a combined output of 12.8 kW.
The heat source specification included a Vaillant aroTHERM 12 kW heat pump and a 300 L Vaillant hot water cylinder. With new extensions and layout changes, the team needed a design process that would confirm sizing decisions quickly and provide documentation suitable for the client and installation crew.
The Challenge
Early guidance suggested a 28 mm primary pipe from the external heat pump to the cylinder. However, long runs, manifold positions, and MCS velocity limits can make seemingly minor pipe choices critical to performance and noise. The team wanted to validate assumptions before committing to materials and install routes.
Traditional spreadsheet methods make what-if checks slow. Verifying velocity, pressure drop, and flow rates across multiple routes, then redrawing for the client, can stretch timelines and introduce errors, especially when design edits arrive late in the day.
The Solution
Grant Store drew the system in h2x, testing the primary run and UFH distribution with real-time calculations. The analysis showed that a 28 mm primary raised velocity to 1.2 m/s, exceeding MCS guidance, while a 35 mm primary kept velocity within limits and protected performance. As Deane Ashcroft said: "Drawing up the model in h2x helped us get the pipe sizes correct and avoid potential issues later down the track."
Beyond the primary, h2x produced a presentable PDF drawing set for client review and automatically generated a Bill of Quantities, simplifying estimating and material orders. Once familiar with the workflow, the team can complete domestic projects in 1-2 hours, including design checks and documentation. "Most importantly, we have accurate pipe sizing calculations for our heat pump installations, which ultimately leads to well-performing systems and happy clients."
The Results
The project progressed with a 35 mm primary to keep velocities compliant and ensure efficient heat transfer from the 12 kW heat pump to the 300 L cylinder. The design package (plans, schedules, and bill of materials) was issued without spreadsheet rework, reducing time on coordination and purchasing.
The combination of accurate sizing, BoM export, and clear drawings improved install confidence and client communication. As Deane puts it, once the process is learned, "we are able to have a domestic project sized in no more than an hour or two."
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