Thermal Response Testing

Onsen Energy operates bespoke industry leading in-house equipment of the highest technical specifications for testing the thermal response of boreholes. Learn more about our professional and efficient services.

Image of Onsen rig

Why use Thermal Response Testing?

A thermal response test (TRT) is the customary method to determine ground thermal conductivity in situ. TRTs, especially for larger ground source heat pump projects (GSHP), provide the data on what’s going on underground for GSHP designers to process and create highly accurate ground loop and system designs.

Knowing the geology means the GSHP design is as accurate as possible: this can save significant upfront drilling costs, and importantly delivers a more accurate & efficient system.

What we do

Drill & Setup

We use our rigs to drill a test borehole on-site. Once we have the test borehole set up, we'll connect it to our in-house TRT test equipment. The test generally needs to happen over a 48-hour period, and we use our own generator to support the energy requirements in this process.

Thermal Response Test

A standard TRT circulates a heated fluid in a test borehole and monitors the temperature values of the ground loop heat exchanger, also measuring stabilised ground temperature, ambient air temperature, flow-rate, and pressure across the loop.


We record and report the results of the TRT to the GSHP designers who can adjust the system design as necessary. On many projects, the results of a TRT can significantly reduce the volume of drilling required, offering large savings.


Once the updated ground loop design is complete, the Onsen team can continue to the next phase by drilling and installing borehole loops, completing headerworks and glycol fill-up.

An astute team that puts safety first

Risk Management

Safety and Compliance

On all potential projects we perform a high level risk assessment: we pride ourselves on our sites' robust health and safety culture. We are GSHPA, British Drilling Association SMAS certified. 

Equipment Maintenance

All equipment and rigs are owned in house - we conduct daily and weekly checks as routine, with a specialist’s assessment at every 500 hours of use.


We are one of the few installers in the UK to offer a comprehensive drilling service - complete with headerworks and glycol fill-up. We’re members of the GSHPA and work with the best GSHP contractors in the UK.

Partners and Certifications

We’re Council members of the Ground Source Heat Pump Association and work hand-in-hand with the UK’s leading Ground Source Heat Pump design team - Genius Energy Lab.

Specialist subcontractors for TRT drilling and GSHP System Installation

If you’re looking for precision on your next GSHP project, get our team’s support. Chat to us further about TRTs and GSHP borehole drilling.

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