Cost Estimation

Costing and Quoting Environmental Test Programs: Cost Per Chamber Hour and Per Test

What actually drives cost per chamber hour and per test, how to build a quote that survives a mid-run chamber trip, and the estimating errors that erode margin.

A reliability lab sells chamber hours, so cost per chamber hour is the foundation of every quote. Build it from four buckets: energy, amortized capital, technician time, and maintenance. A mid-size thermal chamber drawing 18 kW at peak ramp and averaging 9 kW over a profile costs roughly 1.08 dollars per hour at 0.12 dollars per kWh. Capital of 180,000 dollars amortized over 7 years and 3,000 billable hours per year adds about 8.57 dollars per hour. Technician loading at 20% of a 65 dollar fully-burdened hour adds 13 dollars, and maintenance plus calibration reserve adds 4 to 6 dollars. That stacks to roughly 27 to 29 dollars per chamber hour before margin.

Energy is smaller than most estimators fear but spikier than nameplate suggests. Draw is not flat: a chamber pulls near its 18 kW peak during ramps and at temperature extremes, then settles to 6 to 9 kW at a stable dwell. Costing an 85C/85%RH damp-heat run off nameplate power overstates energy by 40 to 60%, while costing a fast thermal-shock profile off dwell power understates it. Energy Cost Per Test multiplies measured average power by profile duration, so a 112-hour thermal job at 9 kW average and 0.12 dollars per kWh is about 121 dollars of electricity, meaningful but far behind capital and labor in the stack.

Capital amortization is the largest and most mishandled line. The per-hour capital charge is capital divided by (useful life in years times billable hours per year), so the denominator, not the sticker price, controls it. That same 180,000 dollar chamber costs 8.57 dollars per hour at 3,000 billable hours but 12.86 dollars per hour at 2,000, a 50% swing driven entirely by utilization. This is why quoting is inseparable from load: a lab running chambers at 60% utilization must bake a higher hourly capital charge into every quote or quietly lose money, while an 85% lab can price sharper and still clear margin.

Labor cost hides in setup, instrumentation, and reporting, not the unattended soak. A 270-hour humidity run may need only 6 to 10 technician hours of active fixturing, channel setup, and interim reads, but a 24-hour HALT run can burn 12 technician hours because setup and teardown dominate. Cost per attended hour, not per calendar hour. Report Labor is a real line too: a formal qualification report routinely takes 8 to 16 engineering hours at 90 to 130 dollars, so a 1,600 dollar report on a 4,000 dollar test program is 40% of the quote and cannot be treated as a throw-in.

Retest and interruption contingency separate a defensible quote from an optimistic one. A chamber trip mid-profile can invalidate cycles already run and force a restart, so a single interruption on a 112-hour thermal job can add days plus energy and labor. Test Interruption Cost and Retest Cost quantify this. If historical trip rate is one restart per 15 long runs and a restart costs roughly 40% of the run, expected contingency is about 0.067 times 0.40, or 2.7% loaded onto the base. Labs that omit this line either eat the restarts or fight the customer over change orders after the fact.

Scrap in a test lab is destroyed samples and consumed articles, and it is real money the buyer's side often forgets. HALT and destructive limit testing consume the DUTs by design, so a program characterizing 12 samples at a 400 dollar unit cost carries 4,800 dollars of hardware scrap that belongs in the quote, not the customer's separate budget. For screening, count the reruns: at 96% first-pass completion on 792 units, about 28.5 units cycle twice, adding chamber time and handling. Fixture fabrication is often a one-time 2,000 to 8,000 dollar tooling line that should be quoted separately from recurring per-unit test cost.

Overhead and margin turn cost into price without pretending they are the same thing. Roll the loaded cost per chamber hour into Test Cost Per Hour, multiply by duration for the direct cost, add setup labor, reporting, scrap, and contingency, then apply overhead of 15 to 30% and a target margin. Lab Quote Price assembles this so a program stays profitable even after a mid-run trip. A common failure is quoting the 27 dollar cost-per-hour as the price: at that number the lab covers electricity and steel but nothing for sales, admin, unbilled calibration, or profit, and margin evaporates on the first schedule slip.

The estimates that go wrong share a pattern: a rate assumed instead of measured. Booking chamber time off empty-chamber ramp rate underquotes duration and therefore every hourly cost tied to it. Costing capital at a 3,000-hour utilization the lab never actually hits inflates the denominator and hides a real loss. Treating the report and setup as free gives away 30 to 50% of the labor. The fix is to price from tracked numbers, load a contingency percentage for interruptions, and quote setup and reporting as explicit lines. A quote that survives one chamber trip and one retest without a change order is the mark of a defensible estimate.

Published 2026-07-01.