Winter Heating and Refrigeration for Bay Area Businesses

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For a Bay Area business, winter heating problems rarely look like a dead furnace. They look like staff in jackets at 8 a.m., a dining room that is warm by the kitchen and cold by the door, an office where one corner roasts while another is freezing, or a walk-in cooler that starts acting up on the first cold nights. Most commercial buildings here are heated by rooftop package units, and most winter complaints trace back to a handful of parts on those units or to how the building brings in outside air.

This page is the business section of our Bay Area Winter Heating Help Center. It covers rooftop heat, economizers and ventilation, restaurants, offices, commercial refrigeration in cold weather, and the rule changes that affect equipment replacement.

Rooftop units: the heat section

A gas-fired rooftop unit has a small furnace built into it: an inducer fan, an igniter, gas valve, burners, a flame sensor, a heat exchanger and a set of limit switches. It may sit idle for heating from April to November, and the first cold morning is when weak parts show up. Common winter calls:

• Tries to light, then locks out. A dirty flame sensor, a worn igniter or a pressure switch that won't prove the inducer. After a few failed tries the control locks out, and a repeated power reset only hides the pattern.
• Blower runs, air is cool. Heat is not firing, the unit is tripping on its high limit (often a clogged filter or slipping belt), or the economizer is letting in too much outside air (below).
• Heat exchanger condition. A cracked or rusted-through heat exchanger can let combustion gases into the supply air. Rooftop units live outdoors in wet winter weather, so this is a standard part of a heating inspection.
• Water and debris. Leaves, clogged drain pans and failed panel gaskets let water in near controls. After storms, see power outages and storms.

For how these units are built, serviced and replaced, our rooftop HVAC master guide for the Bay Area goes deeper.

Economizers stuck open on cold mornings

An economizer is a set of dampers that brings in outside air for free cooling. It is a great feature in fall and spring. In winter, a damper stuck open, a failed actuator or a bad outdoor air sensor can pour cold morning air into the space while the heat section struggles to keep up. Signs: cold air at startup that improves by afternoon, heat that runs constantly without reaching setpoint, and a unit that seems fine when a technician checks it at 2 p.m.

What a technician checks: damper position with the unit in heat mode, the actuator and linkage, the outdoor air and mixed air sensors, the controller settings, and whether the unit has a morning warm-up sequence that keeps outside air at minimum until the space is up to temperature.

Ventilation versus comfort

Commercial buildings are designed to bring in a minimum amount of outside air while people are inside. That is a health requirement, not something to switch off because the room feels cold. The fix for chilly mornings is usually scheduling: start heat early enough that the building is warm when doors open, and make sure the minimum outside air setting is correct rather than wide open. Taping over diffusers or unplugging economizer controls causes other problems, from stale air to equipment faults.

Restaurants: make-up air and drafts

A kitchen exhaust hood pulls a lot of air out of the building, and that air has to be replaced. Where make-up air is untempered or not balanced to the hood, the building runs under negative pressure. In winter that shows up as:

• Cold drafts at the front door every time it opens, and a dining room that never warms up.
• Cold air dumping onto the cook line from the make-up air supply.
• Doors that are hard to open or slam shut.
• Poor draft on gas appliances such as water heaters, which can pull combustion gases back into the space. Treat that as a safety issue, not a comfort issue.

The fix is usually balancing the make-up air to the exhaust, heating the make-up air where the system allows, and interlocking the two so one does not run without the other.

Offices with uneven heat

Perimeter rooms with glass lose heat on cold mornings while interior spaces full of people and computers stay warm. One rooftop unit serving both, controlled from one thermostat, cannot please everyone. Things we look at: where the thermostat is (a sunny wall or a server closet misleads it), duct balancing and dampers, zone controls or reheat boxes that have failed closed, and after-hours schedules that let the building cool too far overnight. A reliable cure for a chronic problem area is sometimes a separate zone or a ductless unit rather than more heat from the main unit.

Commercial refrigeration in cold weather

Winter is not a quiet season for refrigeration. Our senior refrigeration technician Dao Nguyen works on the walk-ins, reach-ins, ice machines and rooftop equipment that see these cold-weather faults:

• Low head pressure. Air-cooled condensers outdoors can run too cold on chilly nights. Head pressure drops, the expansion valve underfeeds the evaporator, and the box runs warm or the evaporator ices even though the weather is cold. Head pressure controls such as fan cycling or a flooding valve are designed to prevent this, and they need to work before the first cold snap.
• Walk-in door and drain heaters. Freezer door frame heaters keep the gasket from freezing to the frame, and drain line heaters keep defrost water flowing. A failed heater means doors that stick or don't seal, ice on the floor, or a frozen drain that backs water into the box.
• Defrost problems. Wet winter air carries moisture into boxes every time the door opens. Weak defrost heaters, a bad termination sensor or a mistimed schedule lead to iced coils.
• Ice machines with remote condensers. Low ambient temperatures affect harvest and production on machines with outdoor condensers.

See commercial refrigeration maintenance, and for a box that is warming up now, emergency commercial refrigeration repair.

Schedule maintenance before the holiday rush

For retail and restaurants, November and December are the worst time to lose heat or a walk-in. A fall heating and refrigeration visit is the best way to avoid an emergency call during your busiest week. A useful fall visit covers:

1. Fire every heat section and watch a full ignition sequence; check the flame sensor, igniter and limits.
2. Inspect heat exchangers and flue paths on gas units.
3. Test economizer dampers, actuators and sensors in heat mode.
4. Replace filters and check belts and blower bearings.
5. Clear drain pans and drains, and check roof curbs and panels for water entry.
6. Set occupied and unoccupied schedules, including morning warm-up.
7. On refrigeration: check head pressure controls, door and drain heaters, gaskets and defrost.

Our commercial HVAC maintenance page describes our service agreements, and energy efficiency tips for rooftop units covers settings that cut winter gas and electric use.

Rules that affect replacement

If a rooftop unit is near the end of its life, two sets of rules are worth knowing before it fails:

• 2025 California Energy Code. It applies to permit applications filed on or after 1 January 2026 (California Energy Commission). For commercial buildings, the Energy Commission says it replaces "certain end-of-life rooftop HVACs with high-efficiency systems, including heat pumps," in buildings such as retail stores, schools, offices and libraries (CEC, Jan 2026). Whether your unit is covered depends on the building and the equipment, so settle it at the quote stage, not after a failure.
• Air District zero-NOx rules. The Bay Area Air Quality Management District lists 1 January 2029 as the zero-NOx date for "residential and commercial furnaces," and 1 January 2031 for water heaters between 75,000 BTU/hr and 2 million BTU/hr (BAAQMD FAQ). The rules apply to new installations only; existing equipment does not have to be removed (BAAQMD). How the furnace rule applies to a particular gas rooftop unit is worth confirming with the Air District as you plan. Our gas furnace rules and heat pumps page has the full timeline.

Planning a replacement on your schedule lets you compare options, line up permits and avoid paying for rush work in a cold week. See commercial HVAC replacement.

Why businesses call Cool Aid

Cool Aid Air Conditioning & Refrigeration has served Bay Area businesses and homes since 1966 from Santa Clara. We hold California C-20 (HVAC) and C-38 (refrigeration) licenses, our technicians are EPA Universal certified, and every job carries a 1-year parts and labor warranty. We handle rooftop units and commercial refrigeration from the same shop, which helps when a restaurant has a heat problem and a walk-in problem in the same week.

Schedule commercial winter service

Frequently asked questions

Written and reviewed by Jim McKinny, owner of Cool Aid Air Conditioning & Refrigeration — California C-20 and C-38 licensed, EPA Universal certified, second generation of a family business serving the Bay Area since 1966. Every job we complete is backed by our 1-year parts & labor warranty.