Introduction
Ground source heat pumps (GSHPs) extract heat from the ground via a buried loop of pipework filled with a water-glycol mixture (brine). The brine circuit operates at temperatures close to or below freezing — creating condensation and frost risks that require careful insulation specification on the above-ground sections of the system.
For a complete overview of heat pump pipe insulation, visit our Heat Pump Pipe Insulation Hub.
This guide covers the correct insulation specification for every pipe on a ground source heat pump installation — brine flow and return, heating distribution, hot water, and the critical connections at the heat pump unit itself.
How a Ground Source Heat Pump Works
A GSHP system has two fluid circuits: the ground loop (brine circuit) and the heating circuit. The ground loop absorbs heat from the ground at low temperatures — typically 0–10°C depending on ground conditions and time of year. The heat pump unit transfers this heat to the heating circuit via a refrigerant cycle, delivering flow temperatures of 35–55°C to the heating distribution system.
The brine circuit pipework — from the ground loop manifold to the heat pump unit — operates at temperatures that can be at or below 0°C in cold weather. This creates a significant condensation risk on the above-ground sections of the brine pipework, which must be insulated with closed-cell elastomeric foam with an intact vapour barrier.
Pipe Runs on a GSHP Installation
1. Brine flow and return (ground loop circuit)
The brine flow and return pipes connect the ground loop manifold to the heat pump unit. Operating temperatures are typically 0–10°C — below the dew point of the surrounding air in most UK indoor environments. Condensation will form on any uninsulated or inadequately insulated surface.
Specification: Closed-cell elastomeric foam with an integral vapour barrier — Armaflex EVO or K-Flex ST. Minimum 19–25mm wall thickness depending on pipe OD and ambient conditions. All joints must be fully bonded with adhesive. See: Vapour Barriers for Pipe Insulation.
2. Heat pump unit connections
The connections at the heat pump unit — where the brine circuit and heating circuit connect to the unit — are frequently left partially uninsulated. These short sections are a significant source of both condensation (on the brine side) and heat loss (on the heating side).
Specification: Insulate all connections fully, including valves, strainers, and flexible connections. Use cut-and-bond elastomeric foam sections for awkward geometries.
3. Heating flow and return
The heating flow and return pipework distributes heat from the heat pump to the heating system — underfloor heating, radiators, or fan coil units. Operating temperatures are typically 35–55°C.
Specification: BS 5422-compliant insulation for the operating temperature and pipe OD. For most GSHP heating circuits, 25mm elastomeric foam or polyethylene foam on pipes up to 35mm OD will achieve compliance. See: BS 5422 Explained.
4. Domestic hot water
Many GSHP systems include a hot water cylinder heated by the heat pump. The pipework connecting the heat pump to the cylinder must be insulated to BS 5422 minimum thicknesses for domestic hot water service. See: What Thickness Pipe Insulation Do I Need?
Condensation Control on Brine Pipework
The brine circuit is the highest-risk section of a GSHP installation from an insulation perspective. The pipe surface temperature can be at or below 0°C — well below the dew point of the surrounding air in a plant room or utility room at 20°C and 60% relative humidity (dew point approximately 12°C).
If the vapour barrier is breached at any joint, fitting, or penetration, water vapour will migrate through the insulation and condense on the cold pipe surface. The insulation will become saturated, its thermal performance will collapse, and corrosion will begin on the pipe surface — often hidden inside the insulation for months before it becomes visible.
Critical installation requirements for brine pipework:
- Use only closed-cell elastomeric foam — Armaflex EVO (μ ≥ 10,000) or K-Flex ST (μ ≥ 7,000)
- Bond all longitudinal seams with Armaflex 520 adhesive — both faces, allow to become tacky, press firmly
- Bond all butt joints with adhesive — stagger joints where possible
- Insulate all valves, strainers, and fittings — no exceptions
- Seal all wall penetrations with fire-rated sealant and insulate up to the wall face
BS 5422 and MCS Compliance
GSHP installations claiming the Boiler Upgrade Scheme grant must be MCS-certified. MCS standards require all pipework to be insulated in accordance with BS 5422 and the heat pump manufacturer's installation manual. See: BS 5422 Resource Centre and Part L Compliance for Pipe Insulation.
For brine pipework, BS 5422 condensation control tables apply — the same tables used for chilled water pipework. See: Chilled Water Pipe Insulation — Complete Guide.
Insulation Thickness Reference — GSHP Brine Circuit
Brine circuit (0°C, ambient 20°C / 60% RH) — Armaflex EVO (λ = 0.033 W/m·K):
| Pipe OD (Nominal) | Minimum Thickness |
|---|---|
| 18mm OD (15mm nominal) | 19mm |
| 22mm OD (22mm nominal) | 19mm |
| 28mm OD (28mm nominal) | 25mm |
| 35mm OD (35mm nominal) | 25mm |
| 42mm OD (42mm nominal) | 32mm |
| 54mm OD (50mm nominal) | 32mm |
Always verify against BS 5422 and the heat pump manufacturer's installation manual.
Frequently Asked Questions
Does the ground loop itself need insulating?
The buried ground loop does not require insulation — it is designed to absorb heat from the surrounding ground. Only the above-ground sections of the brine circuit, from the manifold to the heat pump unit, require insulation.
What insulation should I use on GSHP brine pipework?
Closed-cell elastomeric foam — Armaflex EVO or K-Flex ST. Do not use polyethylene foam or mineral wool on brine pipework — they provide no effective vapour barrier and will fail rapidly.
Why is my GSHP brine pipe dripping?
The most likely cause is condensation forming on the pipe surface due to insufficient insulation thickness, a failed vapour barrier at a joint or fitting, or open-cell insulation that has become waterlogged. Inspect every seam, joint, and fitting for gaps and replace any failed sections with correctly specified Armaflex EVO.
Does GSHP pipe insulation need to comply with BS 5422?
Yes — for heating and hot water pipework, BS 5422 applies in the same way as for any other heating system. For brine pipework, the BS 5422 condensation control tables apply. MCS-certified installations must comply with both BS 5422 and the manufacturer's installation manual.
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