Who this is for: Building owners, facility managers, property managers, and architects dealing with persistent HVAC comfort complaints, rising energy costs, or underperforming mechanical systems in existing buildings.

Summary: Retro-commissioning (retro-Cx) is a systematic process of testing and optimizing existing building HVAC systems to restore performance to original design intent. It typically reduces energy use by 10–20% with 1–3 year payback periods — and it resolves the chronic comfort problems that service calls never seem to fix permanently.

It starts with complaints. A tenant on the third floor says their office is always too hot. Facilities staff get calls every Monday morning about a conference room that never cools down properly. Someone has propped open a stairwell door because the air just feels "stale." Nobody can agree on a thermostat setting that keeps everyone comfortable.

These aren't minor annoyances. They're symptoms — signs that your building's HVAC systems have drifted from how they were originally designed to operate. And the longer the drift goes uncorrected, the more it costs you in energy waste, maintenance calls, tenant turnover, and staff productivity.

The solution is a process called retro-commissioning, and for most existing commercial buildings, it is one of the highest-return investments you can make.

What Is Retro-Commissioning?

Retro-commissioning (retro-Cx) is a systematic process of evaluating, testing, and optimizing an existing building's mechanical, electrical, and control systems — not to redesign them, but to ensure they are operating the way they were intended to. Think of it as a thorough tune-up combined with a diagnostic exam.

It is distinct from new construction commissioning (which verifies systems work at the time of installation) and from renovation or replacement work. Retro-commissioning assumes the equipment is still serviceable — it just isn't performing at its potential.

A typical retro-commissioning engagement includes:

Investigation and benchmarking. An engineer reviews original design documents, current control sequences, maintenance records, and utility bills. This establishes a baseline for how the systems should perform versus how they actually are performing.

Functional testing. The engineer witnesses and tests how equipment actually operates — air handling units, terminal units, controls, sensors, exhaust fans, chilled water systems, boilers. Many issues only reveal themselves when systems are observed under real operating conditions.

Findings and analysis. The engineer documents deficiencies and their likely causes — whether that's a failed sensor reporting incorrect temperatures, an air handler running on a schedule that no longer reflects occupancy, dampers that have never been balanced, or controls reprogrammed during a service call and never restored correctly.

Corrective measures and verification. Recommended fixes are implemented and then verified through follow-up testing to confirm performance has improved.

Why Buildings Drift Out of Tune

Buildings rarely underperform because of a single dramatic failure. More commonly, performance degrades gradually across years of small changes: tenant buildouts alter airflow patterns, control systems are "temporarily" adjusted to handle a complaint and never restored, sensors age and read incorrectly, occupancy schedules change but building automation sequences don't, and maintenance is deferred. Each individual issue seems minor. Together, they add up to a building that routinely frustrates occupants and runs inefficiently around the clock.

This is normal. It happens in virtually every building over time. The question isn't whether your systems have drifted — it's how far.

The Business Case Is Strong

Studies by the Lawrence Berkeley National Laboratory and the Building Commissioning Association consistently show that retro-commissioning delivers significant, measurable results:

• 10–20% reduction in energy use in buildings that have not been previously commissioned, with some achieving even higher savings

• Payback periods of 1 to 3 years for most retro-commissioning investments — one of the fastest-payback building improvement strategies available

• Reduced maintenance costs as equipment operates within intended parameters rather than compensating for system imbalances

• Improved tenant satisfaction and retention, which carries real financial value for building owners and managers

For facility managers facing pressure to meet sustainability goals or reduce operating costs, retro-commissioning is often the most practical first step — because it optimizes what you already have before spending capital on new equipment.

What Gets Uncovered (and Fixed)

While every building is different, common findings in retro-commissioning engagements include:

• Air handling units running at full speed 24 hours a day, including nights and weekends, because occupancy-based scheduling was never set up or was disabled

• Chilled water or hot water valves stuck open or closed, causing simultaneous heating and cooling — one of the most wasteful conditions a building can have

• Temperature sensors that have drifted significantly from calibration, causing the control system to heat or cool in response to inaccurate readings

• Variable air volume (VAV) boxes that were never balanced after a tenant renovation, creating chronically hot or cold zones

• Economizer dampers that are stuck or operating incorrectly, preventing the building from taking advantage of free cooling when outdoor conditions allow

• Demand-controlled ventilation sequences that were disabled at some point and never re-enabled

Many of these issues can be corrected without replacing any equipment — just by restoring systems to their intended operating parameters.

When Should You Commission?

Retro-commissioning is appropriate for virtually any existing commercial, institutional, or mixed-use building, but it is especially valuable in the following situations:

• Buildings more than 5 years old that have never undergone commissioning

• Buildings experiencing persistent comfort complaints that maintenance staff haven't been able to resolve — the classic "problem building" scenario

• Buildings with rising utility costs that can't be explained by occupancy or rate increases alone

• Before a major renovation or equipment replacement — retro-commissioning may reveal that replacement isn't necessary, or it ensures new equipment is installed into a well-functioning system

• Buildings pursuing LEED O+M certification, ENERGY STAR designation, or local benchmarking compliance — retro-commissioning directly supports these goals

Frequently Asked Questions

What is retro-commissioning and how is it different from regular HVAC maintenance?

Retro-commissioning is an engineering-level diagnostic and optimization process. Unlike routine maintenance (filter changes, lubrication, visual checks), retro-Cx involves systematic functional testing of control sequences, sensor accuracy, equipment scheduling, and system interactions — and produces documented findings tied to measurable performance outcomes.

My building has comfort complaints that nothing seems to fix. Will retro-commissioning help?

Almost certainly. Persistent comfort problems — zones that are always too hot or too cold, spaces that never seem to reach setpoint — are the most common sign that systems have drifted from design intent. Retro-commissioning finds the root causes that reactive service calls miss, because it examines the whole system rather than responding to individual symptoms.

How much does retro-commissioning cost?

Costs vary by building size and system complexity. Typical fees for commercial buildings range from $0.10 to $0.30 per square foot. Given average energy savings of 10–20% and payback periods of 1–3 years, retro-commissioning consistently delivers among the highest returns of any building improvement investment.

Can retro-commissioning fix a luxury building with comfort problems?

Yes — and high-end buildings often benefit significantly. Luxury buildings typically have complex, sophisticated HVAC systems with many control sequences, zones, and dependencies. When those systems drift, the comfort impacts are especially noticeable to occupants with high expectations. Retro-commissioning restores the performance that the building was designed — and paid — to deliver.

Does retro-commissioning work on buildings in Utah, Colorado, or Arizona?

Yes. Axiom Engineering Group provides retro-commissioning services throughout the Mountain West, including Utah, Colorado, Arizona, Montana, and Wyoming. Climate-specific factors — like high altitude HVAC performance, dry air, and large diurnal temperature swings — are part of how we approach commissioning in this region.

What is the difference between commissioning (Cx), retro-commissioning (retro-Cx), and re-commissioning?

Commissioning (Cx) verifies that newly installed systems work as designed at the time of construction. Retro-commissioning (retro-Cx) applies a commissioning process to existing buildings that were never commissioned or have since drifted from design intent. Re-commissioning is a repeat commissioning of a building that was previously commissioned. All three share the same core methodology; they differ in when and why they're applied.

Is retro-commissioning required for LEED or ENERGY STAR?

Retro-commissioning is required for LEED O+M (Operations + Maintenance) certification. It also directly supports ENERGY STAR building certification and many local energy benchmarking compliance requirements. Buildings undergoing retro-Cx frequently see their ENERGY STAR scores improve significantly.

How to Get Started

The process begins with engaging a qualified mechanical engineer or commissioning provider to conduct an initial assessment of your building. This typically involves a site walk, review of available documentation, and utility data analysis to identify where the greatest opportunities lie.

From there, a commissioning plan is developed, scoping the investigation and testing work appropriate to your building's systems and complexity.

At Axiom Engineering Group, PLLC, we provide retro-commissioning services as part of our integrated mechanical engineering practice. We understand how systems are designed to work — and what it takes to get them back there. We serve building owners, property managers, and architects throughout the country, including Utah, Colorado, Arizona, Montana, Wyoming, and California.

Axiom Engineering Group works on projects coast to coast. Learn more about our structural, mechanical, plumbing, and commissioning services: aeg.design

About the author: John Melvin, PE, is the CEO of Axiom Engineering Group, an SMEP engineering and commissioning firm with offices in Missoula, MT, Salt Lake City, UT, St. George, UT, and San Diego, CA. John is a licensed Professional Engineer with over 20 years of experience designing mechanical, plumbing, and electrical systems for commercial, institutional, hospitality, healthcare, and luxury residential projects.