NATE Ground Source HP Loop Installer cheat sheet

Heating-dominated loads typically require longer loop fields per ton than cooling-dominated loads because of lower ground temperatures and greater extraction.

Borehole spacing rule of thumb: 15–20 ft (4.5–6 m) center-to-center for vertical loops to limit thermal interference.

Total loop length depends on ground thermal conductivity, borehole thermal resistance, and peak block/ground loads-not just tonnage.

Vertical loop lengths often estimated at 150–250 ft per ton for residential, but must be verified by simulation or ASHRAE methods.

Hybrid systems (loop + cooling tower or boiler) can reduce loop size where peak loads are short-duration.

Series vs. parallel headers: parallel reverse-return equalizes flow; series increases velocity and pressure drop.

Minimum fluid temperature entering heat pump typically 25–40°F depending on antifreeze concentration; design must stay above freeze protection.

Loop design must account for long-term ground temperature drift, not just first-year performance.

Manual J (ACCA) or equivalent room-by-room load calculation is required for sizing; rules of thumb are not acceptable.

Ground thermal conductivity test (thermal response test) provides site-specific data for vertical loop design.

Site survey must identify utilities, setbacks, easements, soil/rock type, water table, and available land area.

Horizontal loop requires approximately 1,500–3,000 sq ft per ton depending on soil and climate; verify with design.

Soil classification (sand, clay, rock) affects drilling method, grout selection, and thermal performance.

Check local codes for well setbacks, groundwater protection zones, and required permits before design.

Load calculation should include block load and peak load; loop sizing uses both.

Document existing HVAC, insulation, and envelope conditions to validate load model inputs.

HDPE pipe for ground loops typically SDR-11 (e.g., 3/4" or 1" IPS) with pressure rating ≥160 psi at 73°F.

PE 3408/PE 3608 resin is common; pipe must meet ASTM D3035 or D2513 and NSF/ANSI 14 for potable water contact if applicable.

U-bend fittings: factory-fused or field-fused; use pre-manufactured U-bends with tested joints.

Grout: bentonite-based or cementitious thermal grout; permeability ≤1×10⁻⁷ cm/s where required.

Antifreeze: propylene glycol (food grade) or ethanol/methanol; concentration based on minimum loop temperature.

Headers: HDPE or copper manifolds; use reverse-return piping and isolation valves for each circuit.

Vaults: pre-cast or HDPE; must be traffic-rated if in vehicle areas and sized for valve access.

Flow center: circulator, expansion tank, air separator, and pressure relief valve; size for loop head loss.

Vertical boreholes typically 4–6 in diameter, drilled to 100–400 ft depth; maintain plumbness within 1–2%.

Horizontal trenches usually 4–6 ft deep, 12–18 in wide; bottom must be free of sharp rocks and debris.

Maintain minimum separation between boreholes and property lines, wells, septic systems, and foundations per code.

Use drilling fluid (mud) or casing as needed to stabilize borehole in unconsolidated formations.

Trench bedding: sand or fine-gravel bedding around pipe; backfill in lifts and compact to avoid settlement.

Slope trench bottom to a low point for purging/drainage; avoid trapped air pockets.

Mark and protect buried utilities before excavation; call 811 or local one-call service.

Record as-built borehole depths, locations, and trench routes for future maintenance.

Butt fusion: heat pipe ends to 500°F ±10°F (260°C), apply interfacial pressure, cool undisturbed per pipe manufacturer's table.

Socket fusion: heat fitting and pipe simultaneously, insert fully, hold without twisting until cool.

Electrofusion: use fittings with barcode or input parameters; ensure clean, dry surfaces and proper scraping.

Pressure test: hydrostatic test at 1.5× design pressure (or per code) for at least 1 hour with no loss; isolate sections.

Test before backfilling; record test pressure, duration, and ambient temperature.

Inspect fusion joints for uniform bead, no gaps, and proper alignment; cut out and re-fuse defective joints.

Use only compatible HDPE materials and fittings; never mix different SDR or resin without manufacturer approval.

Air testing is not permitted for HDPE ground loops; always hydrostatic test with water.

Grout from bottom up using tremie pipe to avoid voids and contamination; displacement method must fill annulus completely.

Thermal grout conductivity typically 0.8–1.4 Btu/(h·ft·°F); bentonite grout ~0.4–0.6.

Grout mix: bentonite or cement-bentonite with water per manufacturer; do not exceed water ratio.

Backfill trenches with approved material free of rocks >1 in; compact in 6–12 in lifts.

Provide sand or fines around pipe to prevent point loading; avoid direct contact with sharp aggregate.

In frost-susceptible areas, use frost-protected backfill or insulation above horizontal loops.

Grout must be placed within 24 hours of drilling or per code to prevent borehole collapse.

Document grout volume used vs. theoretical borehole volume to detect voids or overbreak.

Manifolds should be reverse-return or use balancing valves to equalize flow among circuits.

Install isolation valves on each circuit for flushing and maintenance.

Vault must be watertight, accessible, and sized for valve operation; use traffic-rated cover where required.

Support headers to prevent stress on fused joints; allow for thermal expansion/contraction.

Insulate exposed headers and fittings in vault to prevent condensation and freeze damage.

Pressure-test manifold and header assemblies before burying or enclosing.

Provide drain and air vents at high points; slope header to drain.

Label each circuit and valve with permanent tags for future balancing.

Flush each loop individually at minimum 2 fps velocity to remove debris and air; use a flushing cart with filters.

Flush until discharge water is clear; then purge air by operating at high velocity and venting high points.

Antifreeze concentration must be verified with a refractometer and match design freeze protection.

Fill loop with filtered water and add corrosion inhibitors if specified; maintain pH 7–9.

Perform a final flow test and record flow rates per circuit; balance to design flow ±10%.

Air in loop causes poor performance and pump cavitation; use air separators and purge valves.

Do not use automotive antifreeze; use HVAC-grade propylene glycol or approved fluid.

After flushing, replace filters and verify no leaks under operating pressure.

Follow OSHA excavation rules: protective systems for trenches ≥5 ft deep, ladder access every 25 ft.

Call 811 before digging; wait required time and respect utility markings.

Use personal protective equipment: hard hat, safety glasses, gloves, steel-toe boots, and hearing protection.

Handle antifreeze per SDS; prevent spills to storm drains or waterways; dispose of waste per local regulations.

Grout and drilling fluids must be contained; prevent runoff into surface water.

Obtain required permits for wells, boreholes, and discharge of flushing water.

Lock out/tag out electrical and mechanical equipment before service.

Maintain MSDS/SDS for all chemicals on site and train workers on hazard communication.