NABCEP SHI common mistakes
NABCEP SHI · Understand the traps and how to avoid them.
Fastening collector mounting brackets through roof sheathing only, or into sheathing with short lag screws, instead of locating and lagging into rafters or engineered blocking.
Candidates focus on layout and penetration sealing and treat the roof deck as the structural member; sheathing has almost no pull-out capacity and the mistake is invisible at inspection.
What to do instead
During pre-install, probe or use drawings to map rafter locations, mark them on the roof, and specify fasteners and embedment per the manufacturer's and structural engineer's requirements. Where rafters do not align with the array, install engineered blocking spanning at least two rafters before setting brackets.
Sealing roof penetrations with caulk or roof cement alone, without a flashed standoff or flashing that laps under the roofing course.
Sealant is fast and looks finished, so candidates substitute it for the mechanical flashing detail that actually sheds water.
What to do instead
Use manufacturer-supplied flashed mounts or field-fabricated flashing that integrate with the roofing (lapped under shingles/tiles, counter-flashed on metal roofs), with sealant as a secondary barrier only. Inspect and photograph each penetration before closeout.
Leaving air in the collector loop after fill, either by not purging or by purging at too low a flow, then commissioning with a noisy, cavitating pump.
Candidates fill until pressure appears on the gauge and assume the loop is full; high points and collector headers trap air that only moves at high purge velocity.
What to do instead
Purge at the flow specified by the manufacturer, typically well above operating flow, through a purge valve at the highest point or using a fill/purge cart, until no air or foam discharges. Repeat after the pump has run and the loop has heated, and confirm flow and pump sound at the controller.
Assuming a glycol loop is protected from freezing without measuring the actual concentration after mixing and filling.
Candidates trust the jug label or a mixing ratio calculated on paper, but top-off water, residual water in the loop, and uneven mixing dilute the charge.
What to do instead
Measure with a refractometer at the fill and again at commissioning, and adjust to the concentration in the manufacturer's freeze chart for the local design low temperature. Record the reading and the glycol type on the commissioning sheet.
Mounting the collector temperature sensor on the pipe or strap-clamped to the collector frame instead of in the manufacturer's sensor well on the absorber or header.
Pipe-and-frame locations are easier to reach and wire, but they respond slowly and read cooler than the absorber, so the differential controller runs the pump late and lets the collector stagnate.
What to do instead
Install the sensor dry in the factory well with thermal paste where specified, insulate the well, and route the wire so it does not run in the hot collector casing. Verify the reading against an infrared thermometer at commissioning.
Sizing the circulator from collector count or a rule of thumb without calculating loop head, including pipe, fittings, heat exchanger, valves, and storage tank coil pressure drop.
Candidates match pump curves to collector flow only; the resulting undersized pump produces low delta-T, high collector temperatures, and poor stratification.
What to do instead
Calculate head at design flow for the full loop, select a pump with its operating point inside the efficient range, and confirm actual flow at commissioning with a flow meter or by measuring delta-T and comparing to the design value.
Doing a shade survey only at midday in summer, or eyeballing obstructions, instead of evaluating the solar window across the heating season.
Summer sun is high and clears trees and buildings that block low winter sun, so the array looks clear when winter output will be badly reduced.
What to do instead
Use a solar pathfinder, Solmetric-type tool, or a fisheye photo analysis, and evaluate the whole year with emphasis on the heating-season months and the 9 a.m. to 3 p.m. window. Note deciduous versus evergreen vegetation and expected growth.
Treating the structural review as a formality, approving an array on a roof without confirming dead load, wind uplift, and attachment capacity for the specific collector and mounting system.
Candidates assume residential roofs are overbuilt and reuse details from a previous job without checking span, snow load, or the mounting manufacturer's engineering.
What to do instead
Obtain or produce a load calculation for the array weight plus snow and wind, compare against the mounting system's listed span and attachment ratings, and get engineered stamped details where the jurisdiction or site conditions require them.
Commissioning the system without confirming the tempering or anti-scald valve, the tank T&P relief valve, and the overheat/stagnation protection are installed, correctly rated, and functioning.
Candidates focus on flow, pressure, and controls and treat safety devices as the plumber's scope, so a missing or wrong-rated relief valve goes unnoticed.
What to do instead
Walk the safety checklist at commissioning: verify T&P rating and discharge piping, confirm tempering valve outlet temperature, and test the stagnation sequence by simulating a high-limit or pump-off condition and observing the controller response. Document each check.
Working on the roof or on live pump/controller circuits without a fall-protection setup or lockout/tagout, improvising harness anchors or troubleshooting energized controls.
Candidates treat small residential jobs as low hazard and skip the setup time, and they troubleshoot controls live because de-energizing resets the fault.
What to do instead
Establish anchor points and use a harness and lanyard or guardrails whenever the fall exposure triggers the requirement, and de-energize and lock out the controller and pump circuits before servicing. Where live diagnostics are unavoidable, use a qualified second person and appropriate PPE.