Facility managers in Arlington and Fort Worth may assume that constantly running reheat coils are normal during winter operation. They are not.

Excessive runtime may be a sign that something in the VAV system is working against itself, driving up winter utility bills, increasing tenant overheating complaints and generating trend data that reveals simultaneous heating and cooling.

Reheat is intended to fine-tune space temperature, not carry the bulk of the heating load. When it operates for long stretches or across large portions of a building, mechanical or configuration issues are usually driving the problem.

When Reheat Becomes a Cost Signal

Common reheat runtime warning signs tend to appear before anyone looks at the data:

• Spaces may feel stuffy or overly warm even on mild days
• Interior zones overheat while perimeter zones struggle to stabilize
• Utility costs climb despite relatively short heating seasons

In many cases, the system is technically maintaining setpoint, but doing so inefficiently. These symptoms often point to airflow or valve problems rather than a lack of heating capacity.

Why Excessive Reheat Matters in Heating Season

During heating season, VAV systems operate with lower airflow targets and tighter control tolerances. That makes inefficiencies easier to spot in both comfort complaints and energy use.

Reheat coils that run excessively are compensating for another imbalance, and the longer that compensation continues, the more it costs in energy and equipment wear.

Damper Calibration Errors That Drive Reheat Demand

VAV box dampers that are out of calibration are a frequent cause of excessive reheat. The box may deliver more air than intended when a damper does not match its commanded position. That excess airflow cools the space, forcing the reheat coil to add heat just to maintain temperature.

Even small position errors multiplied across dozens of boxes can add up to significant runtime and energy waste.

Leaky or Passing Heating Valves

A valve that leaks hot water through the coil continues adding heat even when reheat is not called for. The system responds by adjusting airflow or cooling elsewhere, creating a loop of unnecessary heating and correction.

Passing valves are especially difficult to detect without inspection or trending. The space may appear comfortable, but the reheat coil is quietly running longer than it should, driving up winter utility costs and shortening valve and actuator life.

Minimum Airflow Settings That Are Too High

Improper minimum airflow settings are one of the most frequent contributors to excessive reheat runtime. Many VAV systems are configured with minimums based on cooling or ventilation assumptions that no longer match actual space use.

When minimum airflow is set too high, the box delivers more air than needed in heating season. Reheat is then forced to counteract that airflow just to maintain setpoint. This condition is especially costly in buildings with many interior zones, where heating loads are already low.

Adjusting minimums to reflect real heating needs can dramatically reduce reheat runtime without affecting comfort or ventilation.

Load Mismatch Between Cooling and Heating Design

VAV systems are fundamentally cooling-driven by design. In winter, those systems rely on reheat to correct a mismatch between how air is distributed and how spaces actually gain or lose heat.

Interior zones often require little to no heating, while perimeter zones fluctuate with outdoor conditions. When the system treats these areas similarly, reheat becomes the tool used to force balance. The result is prolonged operation that feels normal in practice but inefficient in reality.

Why These Issues Often Go Uncorrected

Excessive reheat is easy to overlook because it feels to occupants as if the system is working properly. Inefficiency is often tolerated as long as tenants aren’t reporting problems.

Without targeted diagnostics, reheat may be dismissed as a normal part of winter operation rather than a signal of mechanical or configuration problems.

Diagnosing Reheat Problems and Finding the Right Solution

Adjusting schedules or setpoints may not address the underlying issue causing excessive reheat runtime. Implementing the right solution that fixes the source of VAV problems can reduce winter energy spend and improve overall system stability across every season.

If you suspect VAV system reheat problems, call Tom's Commercial at (817) 857-7400.