Commercial Heating Repair: What a Building Owner Should Look For

Which heat source the building has

PNNL's best practice page on unitary HVAC equipment says it can provide cooling only, heating only, or both. It lists gas (natural or propane), electric resistance and the air-to-air heat pump among the system types that can provide the heat. All the parts can sit in one cabinet, such as a rooftop unit, or in two cabinets as a split system. EIA defines a packaged unit as equipment assembled at a factory and installed as a self-contained unit. EIA says packaged units are generally mounted on the roof and produce warm or cool air directly. Its list of heating equipment also names boilers, furnaces, individual space heaters, duct reheat, and district steam or hot water piped in from outside.

Federal rules define commercial furnaces and boilers in the Code of Federal Regulations (CFR). Under 10 CFR 431.72, a commercial warm air furnace is a warm air furnace that is industrial equipment and that has a capacity (rated maximum input) of 225,000 Btu per hour or more. The same section defines a warm air furnace as a self-contained oil-fired or gas-fired furnace designed to supply heated air through ducts to spaces that require it. It says the term includes combination warm air furnace/electric air conditioning units but does not include unit heaters and duct furnaces. Under 10 CFR 431.82, a commercial packaged boiler must meet all of four listed criteria, and one of the criteria is a rated input of 300,000 Btu/h or greater. These are input figures, so ask whether a quote is talking about input or delivered heat.

Tampa's heating load is small and short

The National Weather Service (NWS) Tampa Bay office publishes 1991 to 2020 normals for Tampa. They list 433 heating degree days a year, against 3,611 cooling degree days. EIA defines a heating degree day as how far a day's average temperature falls below 65°F, summed over the year. The normals list 105 heating degree days in December, 152 in January and 88 in February. June, July and August show zero. The same NWS sheet's records, which begin in 1890 and run through 2023, list the most heating degree days in one year as 1,117 in 2010 and the fewest as 186 in 2017.

Carrier's service manual for its 48TC rooftop line says to inspect the main burners at the beginning of each heating season. It says to look for deterioration or blockage due to corrosion or other causes. Our reading: book the heating check in the fall, before the first cold front, not after the first complaint.

Gas heat in a rooftop unit: parts, safeties and fault codes

Carrier's 48TC manual describes a gas valve feeding multiple inshot burners off a manifold, which fire into the heat exchanger tubes. The manual says the secondary tubes exit into a collector box and then into the induced draft fan wheel inlet, and the fan wheel discharges into a flue passage, with flue gases exiting out a flue hood on the side of the unit. The safety switches are a rollout switch at the top of the burner compartment and a limit switch over the tubes. The Integrated Gas Unit Controller (IGC), in the control box, carries a single diagnostic light. That light is a light-emitting diode (LED), and the manual says it can be observed through a viewport.

The manual's code table lists 2 flashes as a limit switch fault and 3 flashes as a flame sense fault. It lists 5 flashes as an ignition lockout, 6 as an induced-draft motor fault and 7 as a rollout switch fault. Four flashes means 4 consecutive limit switch faults within a single call for heat. The manual says a break in power resets the IGC, with a loss of fault history. Our reading: have staff write down the flash count before anyone cycles power. A rollout fault or repeated limit faults are a reason to leave the unit for a licensed contractor, not to keep resetting it.

For a limit switch fault, the manual's probable cause is that the high temperature limit switch is open. Its listed checks include the indoor fan motor, the supply-air temperature rise against the nameplate range, and the return air filters. Its heating service table lists a dirty air filter, restricted airflow and too much outdoor air among the causes of inadequate heating. Our reading: the return air filters are something facility staff can check before calling. Manifold pressure, the burners and the flame sensor are a technician's checks. The rooftop unit not running page covers a unit that will not start at all.

Electric heat and heat pumps

PNNL says an electric heating system generally has resistance heater elements, heater controls and safety devices. It names an airflow switch and over-temperature protection, which de-energize the heater when unsafe conditions are detected. PNNL's maintenance checklist includes making sure the electric heat only energizes when there is airflow. It also lists checking the temperature rise and the supply air temperature.

A heat pump is heating and cooling equipment that draws heat into a building from outside, and ejects it outside in the cooling season, in EIA's definition. EIA adds that its indoor and outdoor coils are used reversibly as condensers or evaporators. PNNL says an air-to-air heat pump adds a reversing valve and an accumulator to the parts of a cooling system. Its checklist asks for confirmation that the unit works in both cooling and heating mode, with the reversing valve operating properly. A 2013 PNNL re-tuning training deck (a set of course slides) says to verify that heat pump defrost cycles work, because heavily iced outdoor coils will not function correctly.

The same deck covers packaged heat pumps with auxiliary electric heat (backup heat from electric elements). It says setbacks can increase a building's electric demand significantly during morning warm-up. It advises checking for an outdoor air temperature lockout on that heat and, if one exists, setting it at the lowest possible outdoor temperature. Our reading: asking what that setting is fits a service visit, while changing controller programming belongs to the controls contractor. EPA requires technicians who maintain, service, repair, or dispose of equipment that could release refrigerants into the atmosphere to be certified. EPA Section 608 refrigerant rules explains what that certification covers.

Boilers and hot-water heat

PNNL's Operations and Maintenance Best Practices guide, written for the Department of Energy's Federal Energy Management Program, defines boilers as fuel-burning appliances. It says they produce hot water or steam that is circulated through piping for heating or process uses. It sorts boiler designs into fire-tube, water-tube and electric. In a fire-tube boiler, hot gases circulate through tubes submerged in water. In a water-tube boiler, gases flow over water-filled tubes. The guide says fire-tube boilers are generally available in the range 20 through 800 boiler horsepower, and says that in terms of Btu output, 1 bhp equals 33,475 Btu/hr. By our arithmetic, that is about 670,000 to 26.8 million Btu/h of output, not rated input.

The guide says boiler inspections should be performed at regular intervals by certified boiler inspectors. It says frequent cycling in a gas-fired boiler is usually a sign of insufficient building or process loading. It says combustion efficiency is typically measured through the percent oxygen in the exhaust gas, and that boilers should be operated with some excess air to ensure complete and safe combustion. It names a combustion analyzer as the tool that reports combustion efficiency for boilers, furnaces and water heaters. Our reading: ask the contractor for the printed combustion analysis, not only a note that the boiler was checked. Pumps and piping on the water side are covered on pump and hydronic services.

Combustion safety, licensing and questions to ask

EPA lists worn or poorly adjusted and maintained combustion devices, such as boilers and furnaces, among the sources of carbon monoxide (CO). It adds a flue that is improperly sized, blocked, disconnected or leaking. EPA says it is most important to be sure combustion equipment is maintained and properly adjusted. Carrier's manual tells anyone who smells gas not to light any appliance, touch any electrical switch or use any phone in the building. It says to call the gas supplier from a neighbor's phone and to follow the gas supplier's instructions, and to call the fire department if the supplier cannot be reached. Furnace heat exchanger cracks covers cracks and CO risk in more depth.

PNNL's gas heating checklist includes checking the heat exchanger for cracks, rust and soot, and checking draft and analyzing combustion. It also lists testing the ignition system and the safety shut-off response, and checking the flue or vent pipe for rust and corrosion. PNNL says a trained and authorized HVAC professional typically performs repairs. It says facility maintenance staff can do visual inspections and routine checks and document issues. It recommends a written log, preferably in a Computer Maintenance Management System. For a written standard, PNNL points building engineers to Standard 180 (from ASHRAE and ACCA, two industry bodies), a standard practice for inspecting and maintaining commercial building HVAC systems.

Under the 2026 Florida Statutes, a Class B air-conditioning contractor is limited to 25 tons of cooling and 500,000 Btu of heating in any one system, among other limits. The statute's scope for both Class A and Class B does not include any work such as liquefied petroleum or natural gas fuel lines within buildings, except for disconnecting or reconnecting changeouts of liquefied petroleum or natural gas appliances within buildings. Put these questions to the contractor, and get the answers in writing.

1. Which heat source is this: gas, electric resistance, a heat pump, or a boiler loop?
2. What rated input in Btu/h and what temperature rise range does the nameplate give?
3. What fault code or alarm was showing, and was it written down before power was cycled?
4. Did the visit include a combustion analysis and a heat exchanger inspection, and can we have the readings?
5. For a heat pump, were defrost and any auxiliary heat lockout checked, and what is the lockout set to?
6. Which Florida license class does the contractor hold, and does its scope cover this system?