Fault Detection Cost Calculator
FDD system cost and energy savings from fault correction.
About this calculator
This calculator estimates the first-year cost and ongoing return on a fault detection and diagnostics (FDD) system from equipment counts, BAS point count, and Building Age. First-Year Total Cost is driven almost entirely by equipment count (Number of AHUs plus Number of VAV boxes, both feeding Implementation Cost and Training Cost) and Total BAS Points (feeding Annual FDD Software Cost) -- Number of VAV boxes is the dominant lever at this calculator's defaults because VAV terminal units typically outnumber AHUs many times over in a real building.
Building Age is a genuine mode switch: it selects a different energy-savings rate (7% for new buildings, 14% for mid-age, 20% for old), maintenance-savings rate, comfort-savings-per-unit figure, and faults-per-unit rate all at once, which is why an older building shows a substantially larger Net Annual Benefit and a shorter Simple Payback than a new building with identical equipment counts and energy costs -- older HVAC systems accumulate more correctable faults, so FDD finds proportionally more savings in them. Annual HVAC Energy and Annual Maintenance Cost only affect the savings side of the calculation (Energy Savings and Maintenance Savings respectively); they never appear in First-Year Total Cost, Implementation Cost, or Annual FDD Software Cost, which are computed purely from equipment and point counts.
Inputs
Results
First-year total cost ($)
$20,800.00
≈ 10 gaming PCs
Net annual benefit ($)
$55,260.00
Simple payback (years)
0.4
How to Use This Calculator
- Enter Total BAS points, Number of AHUs, and Number of VAV boxes.
- Set Annual HVAC energy ($), Annual maintenance ($), and Building Age.
- Adjust New (0-5 years), Mid-age (5-15 years) as needed.
- Review First-year total cost ($) ($), Net annual benefit ($) ($), and Simple payback (years).
- Use Implementation cost ($) ($) and Annual software ($) ($) to inform your decision.
How the result changes with Number of VAV boxes
| Number of VAV boxes | First-year total cost ($) | Net annual benefit ($) | Simple payback (years) |
|---|---|---|---|
| 30 | $16,800.00 | $47,910.00 | 0.4 |
| 45 | $19,300.00 | $51,585.00 | 0.4 |
| 90 | $23,800.00 | $62,610.00 | 0.4 |
| 150 | $31,800.00 | $77,310.00 | 0.4 |
What each input means
- Total BAS points
- Total building automation system points. FDD software is often licensed per point.
- Number of AHUs
- Air handling units — primary FDD targets for simultaneous heating/cooling, economizer faults.
- Number of VAV boxes
- Variable air volume terminal units — common faults include stuck dampers, reheat valve failures.
- Annual HVAC energy ($)
- Annual HVAC energy cost (heating + cooling + fans/pumps). FDD typically saves 7-20% of this.
- Annual maintenance ($)
- Annual HVAC maintenance budget. FDD reduces reactive maintenance by 8-20%.
- Building Age
- Select building age category
What each result means
- First-year total cost ($)
- Implementation + software + training cost for the first year.
- Net annual benefit ($)
- Total annual savings minus ongoing FDD costs.
- Simple payback (years)
- Years to recover first-year investment from net annual benefits.
- Implementation cost ($)
- One-time cost for integration, setup, and system tuning.
- Annual software ($)
- Yearly FDD software/platform license cost.
- Energy savings ($/yr)
- Estimated annual HVAC energy savings from detecting and correcting faults.
- Maintenance savings ($/yr)
- Annual maintenance cost reduction from predictive vs. reactive maintenance.
- Total savings ($/yr)
- Combined energy + maintenance + comfort complaint savings.
- 5-year ROI (%)
- Return on investment over a 5-year period.
- Est. faults detected/yr
- Estimated number of actionable faults detected per year.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTotal BAS points = 500, Number of AHUs = 8, Number of VAV boxes = 60, Annual HVAC energy ($) = 200000 = 6 input(s) provided
- Calculate First-year total costFirst-year total cost = implementationCost + annualFDDSoftwareCost + trainingCost20800 = $20,800
- Calculate Net annual benefitNet annual benefit = totalAnnualSavings - annualOngoingCost55260 = $55,260
- Calculate Simple payback0.4 = 0.4
- Calculate Implementation costImplementation cost = implementationBase + totalEquipment * implementationPerUnit14800 = $14,800
- Calculate Annual softwareAnnual software = totalBASPoints * fddCostPerPointPerYear1000 = $1,000
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
How does this estimate compare to a real implementation quote from an FDD software vendor?
Treat it as a planning-level estimate built from published PNNL and LBNL cost ranges and a flat per-point software rate, not a substitute for an actual proposal. A real vendor quote will move based on which platform you choose (cloud-hosted versus an on-premise server), how well it integrates with your existing BAS brand out of the box, and whether your facility needs custom fault rules built beyond the vendor's standard library -- use this tool to gauge whether FDD looks feasible before you issue an RFP, not to lock in a final capital number.
Why does an older building show better FDD payback than a new one?
Building Age selects a different savings rate for energy (7%/14%/20% for new/mid-age/old buildings), maintenance (8%/15%/20%), comfort-complaint reduction, and faults detected per year -- all simultaneously. Older HVAC equipment accumulates more correctable faults (stuck dampers, sensor drift, simultaneous heating/cooling), so FDD finds proportionally more savings there even at identical energy and maintenance spending.
Does my annual HVAC energy cost change the first-year investment?
No. Annual HVAC Energy Cost only feeds Energy Savings ($/yr), which is part of the ongoing benefit calculation -- it never appears in First-Year Total Cost, Implementation Cost, or Annual FDD Software Cost, all of which depend only on equipment counts and BAS point count.
What counts as an 'equipment unit' for implementation cost?
Total Equipment is the sum of Number of AHUs and Number of VAV boxes. Implementation Cost adds $100 per equipment unit on top of an $8,000 base, and Training Cost adds $1,000 for every 50 equipment units on top of a $3,000 base -- so a facility with many small VAV zones scales this cost the same way as one with fewer but larger AHU systems, unit for unit.
Why does the simple payback stay so short across different scenarios?
Because Net Annual Benefit combines energy savings, maintenance savings, and comfort-complaint savings, while First-Year Total Cost is comparatively small (an implementation base plus a modest per-unit and per-point rate) -- studies this calculator is based on (PNNL, LBNL) generally find FDD paying for itself within a few years, and this model reflects that by scaling savings across three separate categories rather than one.
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