Retro-commissioning (RCx): process, cost and savings

Most commercial buildings were never fully commissioned, and the ones that were have usually drifted since. Schedules get extended, setpoints get changed after complaints, sensors drift and control sequences get disabled during callouts. Retro-commissioning (RCx) is the process that finds and fixes that drift in an existing building, usually without buying new equipment.

This guide covers what RCx is, which buildings need it and how often, what it typically finds, the step-by-step process, what it costs and saves according to the largest published study, why the savings fade and how to keep them, and how to choose a provider.

Key takeaways

• RCx tunes an existing building's systems to work as they should, mostly through low-cost operational fixes rather than new equipment.
• It is inexpensive and pays back quickly. Lawrence Berkeley National Laboratory (LBNL) puts the median cost of existing-building commissioning at $0.26 per square foot, with a median simple payback of 1.7 years.
• Several US jurisdictions require it, including New York City every ten years and Los Angeles and Seattle every five years.
• One-off savings fade. Studies from the early 2000s found around a third of RCx savings were lost over time when nobody kept watching.
• Verification and ongoing monitoring keep the savings, which is why many utility programs now pair RCx with monitoring-based commissioning (MBCx).

What is retro-commissioning (RCx)?

Retro-commissioning (RCx) is a systematic process for finding and fixing operational problems in an existing building that was never commissioned, so its HVAC, controls and other systems run as efficiently as the building's current use requires. Most RCx fixes are low-cost changes to schedules, setpoints, control sequences and sensors rather than equipment replacement.

The US Department of Energy separates the related terms clearly in its EISA section 432 guidance: commissioning applies to new construction, re-commissioning to an existing building that was commissioned before, and retro-commissioning to an existing building that never was. In practice, many programs group re-commissioning and retro-commissioning together as existing building commissioning (EBCx), because the work is largely the same.

For new buildings, see our guide to building commissioning and HVAC commissioning. For the continuous version of RCx, see our complete guide to monitoring-based commissioning. For every type side by side, with costs and savings, see Cx vs RCx vs MBCx compared.

Which buildings need retro-commissioning, and how often?

RCx suits existing commercial buildings with a building management system and central HVAC plant, particularly those with rising energy use, comfort complaints or no commissioning record. A common rule of thumb is every three to five years, or sooner after a change of use, major tenant turnover or controls upgrade. Some US cities set the interval by law.

Warning signs that a building is due for RCx include:

• energy use rising with no change in occupancy or weather to explain it;
• frequent hot and cold complaints, often in the same zones;
• plant running at night and at weekends;
• many points left in manual override;
• settings nobody on site can explain;
• no commissioning record or current sequences of operation.

Several US jurisdictions make RCx, or an equivalent tune-up, a legal requirement:

Building performance standards such as NYC Local Law 97 and Boston's BERDO do not require RCx directly, but they set limits a building must meet every year from measured data. That makes RCx one of the cheapest compliance levers available.

What does retro-commissioning typically find?

RCx typically finds plant running outside occupied hours, simultaneous heating and cooling, leaking or stuck valves and dampers, failed or drifting sensors, overrides left in place, economizers that never enable and reset strategies that were never commissioned. None of these trip a BMS alarm, which is why they persist for months or years.

The pattern is consistent at scale. In CIM's analysis of fault alerts across 600+ commercial buildings, out-of-hours operation and sensor faults each affected 78% of buildings, while the most expensive individual faults were passing valves and overrides left in place. Our breakdown of the most common HVAC faults in commercial buildings shows the signature each one leaves in the data.

The retro-commissioning process, step by step

RCx moves from planning through investigation, implementation and verification to hand-off. Investigation, where the provider works out what is wrong and why, is usually the longest and most expensive phase. Verification, confirming that each fix actually held, is the step most often skipped.

1. Planning and scoping. Set goals, gather drawings, sequences of operation, utility bills and at least 12 months of interval data, interview operators and agree which systems are in scope.
2. Site assessment. Walk the plant and check overrides, schedules, setpoints and the condition of sensors, valves and dampers.
3. Data logging and diagnostics. Trend BMS points or install short-term loggers to see how systems behave across occupancy and weather. Fault detection and diagnostics (FDD) software does much of this automatically and across every point, not a sample.
4. Findings and prioritization. List operational issues and energy conservation measures with estimated savings, cost and payback, and rank low-cost, high-impact fixes first.
5. Implementation. The owner's team or contractors correct schedules, setpoints, sequences, sensors and mechanical faults. Our guide to costing remedial works covers what a maintenance contract usually already includes.
6. Verification. Confirm each fix in the data across a full operating cycle, not just at the end of the site visit, and measure savings against an adjusted baseline. Our guide to measurement and verification explains the method.
7. Hand-off and persistence. Update documentation, train operators and set up ongoing monitoring so the savings do not drift away again.

Many US utility programs fund part of the investigation and pay incentives on verified savings, so check what your utility offers before you scope the project.

How much does retro-commissioning cost and save?

The largest published study, by Lawrence Berkeley National Laboratory, found a median cost of $0.26 per square foot for commissioning existing buildings, with a median simple payback of 1.7 years. Median energy savings ranged from 5% for projects in utility programs to 14% for projects outside them.

The figures below come from LBNL's analysis of commissioning in 1,500 North American buildings (Crowe et al., 2020), with earlier benchmarks for context.

At the median cost, RCx on a 100,000 sq ft office would cost around $26,000. Cost depends more on the number and complexity of systems, data access and how much of the investigation is automated than on floor area alone. Medians also hide a wide range: some projects save far more, and some very little. For how savings and costs compare when RCx becomes a continuous program, see the cost section of our MBCx guide.

Why do retro-commissioning savings fade, and how do you keep them?

RCx savings fade because most of them come from operational settings that are easy to undo: a callout puts a unit in hand, a complaint drops a setpoint, a sensor drifts. Research from the early 2000s found around 35% of savings lost over time after one-off RCx. Verified close-out and continuous monitoring are what keep them.

That finding, summarized in an ACEEE paper on the evolution of monitoring-based commissioning, is what pushed utility programs toward permanent metering and trending. The same gap appears at close-out. In a CIM sample of closed fault tickets, about 1 in 6 were closed before the building data confirmed the fix, as we explain in how to verify a contractor actually fixed a fault.

Monitoring-based commissioning is the answer most programs have settled on: permanent metering and analytics keep checking after the RCx project ends. In LBNL's data, utility programs that added submetering and diagnostics achieved median savings of 9%, against 5% for standard utility commissioning programs. Some programs now require a recent RCx before they will fund MBCx. Colorado's Efficiency Works, for example, positions MBCx as the way to sustain and deepen retro-commissioning savings.

How do you choose a retro-commissioning provider?

Choose an RCx provider with recognized commissioning credentials, experience on buildings like yours, a clear method for verifying fixes in the data and a plan for keeping savings after the project ends. Ask how findings and savings will be reported, and who owns the data and the issues list afterward.

How does CIM's PEAK Platform support retro-commissioning?

CIM's PEAK Platform is used by commissioning and engineering firms to speed up RCx and keep its savings in place. It supports three parts of the work:

• Investigation. PEAK reads the existing BMS across all major brands and replaces most of the manual trend analysis with a ranked, diagnosed fault list covering every point.
• Verification. Each fault stays linked to the rule that raised it, so a fix is only confirmed when the fault condition clears in the data, and the issue reopens if it returns.
• Persistence. The same platform carries on after the project as an MBCx service, so the client keeps the savings and the provider keeps a recurring relationship.

Aero Performance Group, a Chicago-area RCx and MBCx provider, grew its active project portfolio by 50% without adding resources and now verifies around 6 million kWh of energy-saving incentives a year for its clients. Its team talks through how fault data changed their delivery in our webinar on how FDD improves RCx and MBCx outcomes. See how PEAK supports retro-commissioning projects, or read how engineering firms run RCx and MBCx on FDD.

Frequently asked questions

What is the difference between retro-commissioning and re-commissioning?

Retro-commissioning applies to an existing building that was never commissioned. Re-commissioning applies to an existing building that was commissioned before and has since drifted. The process is largely the same, which is why many programs group both under existing building commissioning (EBCx).

How much does retro-commissioning cost?

Lawrence Berkeley National Laboratory found a median cost of $0.26 per square foot for commissioning existing buildings, based on 2018 data, with a median simple payback of 1.7 years. Actual cost depends on the number and complexity of systems, data access and scope, and utility incentives often offset part of it.

How long does retro-commissioning take?

Most RCx projects take several months from planning to verification, depending on building size, data access and how quickly fixes are implemented. Seattle City Light's existing building commissioning program, for example, allows 4 to 12 months for the commissioning phase.

How often should a building be retro-commissioned?

A common rule of thumb is every three to five years, or sooner after a change of use or major tenant turnover. Some jurisdictions set the interval by law: every ten years in New York City, every five years in Los Angeles and Seattle, and every four years for covered US federal facilities. Monitoring-based commissioning makes the process continuous.

Who can perform retro-commissioning?

RCx is usually performed by a commissioning provider or engineering firm with recognized credentials such as CxA, BCxP or CCP. Owners with in-house engineers can carry out much of the work themselves, especially with fault detection software doing the investigation, but some mandates and incentive programs require a qualified third-party provider.

Is retro-commissioning required by law?

In some US jurisdictions, yes. New York City's Local Law 87 requires retro-commissioning every ten years for buildings over 50,000 square feet, Los Angeles requires it every five years under EBEWE, Seattle requires building tune-ups every five years, and federal agencies must implement recommissioning and retro-commissioning measures under EISA section 432.

What is the difference between RCx and MBCx?

Retro-commissioning is a periodic project that finds and fixes problems at a point in time. Monitoring-based commissioning (MBCx) uses permanent metering and analytics to find problems continuously and verify that fixes hold. MBCx usually follows an RCx project to keep its savings from fading.

Does retro-commissioning require new equipment?

Usually not. Most RCx measures are operational changes to schedules, setpoints, sequences and sensors. An RCx investigation may identify capital measures worth doing, and some projects add meters or sensors to improve visibility, but the core savings come from making existing equipment run as it should.