Commercial HVAC replacement and installation in San Mateo.

Most buyers are choosing among three paths, and the right one depends on how much life the rest of the building has left.

Running to failure feels cheapest until the unit dies in season and you take whatever tonnage is on a truck. DOE is blunt about the pattern: facility managers often delay until the unit no longer conditions the space, needs constant service, or quits entirely, and that delay usually costs more than a planned swap would have.

Advanced controls are the middle path. DOE's Advanced RTU Campaign treats both routes as legitimate — replace the unit, or retrofit it with advanced controls — and which one wins is a financial question about that specific unit, not a rule.

Full replacement resets the clock. It is the only path that corrects sizing, brings the unit to current efficiency, and gives you a warranty and a known service life to plan against.

Nobody can quote a rooftop unit from a satellite view. These are the lines that separate a clean same-curb swap from a construction project, and most of them are only settled once someone stands on the roof.

The biggest equipment decision on a San Mateo roof today is not the brand on the cabinet. It is whether the replacement burns gas at all.

DOE's heat pump rooftop guidance sorts this by climate first. Heat pump efficiency drops as outdoor temperatures fall, so heat pump rooftop units suit mild to moderate winter heating best. For most of the U.S. South and West, DOE says today's heat pump units are an appropriate solution and are capable of addressing most or all of the winter heating demand. A mild coastal site sits squarely inside that description, which is why the all-electric option deserves a real evaluation here rather than a polite dismissal.

Climate is only the first gate. DOE's checklist also weighs local electricity and gas prices, grid emissions, building type, equipment availability, electrical capacity, physical constraints on the roof, existing gas lines, contractor familiarity, and available incentives. Any one of those can send a specific building back toward gas heat, or toward a dual-fuel unit that runs on the heat pump most of the year and lights the burner on the coldest mornings.

The practical move is to price two options on your actual roof instead of picking a technology in the abstract. If the electrical service has headroom, the all-electric case usually holds. If a panel upgrade is required, that cost belongs in the comparison before anyone calls one option cheaper.

Two buildings on the same block can get very different numbers for the same tonnage. The difference is almost always access, structure, and what the new unit needs that the old one never did.

A quote written without a roof visit is a guess with a number attached. The site review exists to turn unknowns into line items before you sign anything.

Start with the load. Twenty years changes occupancy, plug loads, lighting, and often the envelope itself. The old nameplate tells you what someone sized in a different decade, not what the space needs now. Confirming the load either validates a like-for-like swap or finally explains a comfort complaint the building has lived with for years.

Then come the physical constraints DOE names directly: electrical capacity at the panel, room on the roof and around the curb, and where the existing gas lines run. Those three decide whether an all-electric unit is a swap or a small construction project.

Access is the third piece — crane reach, staging, which stalls close, and for how long. Tenants tolerate a planned morning of cones far better than a surprise afternoon of them.

Last is the old unit itself. EPA Section 608 rules govern how refrigerant is recovered and handled when equipment comes down, so recovery and documentation are part of the job rather than an afterthought.

California cities treat mechanical work as permitted work. Local building departments require permits for electrical, plumbing, and mechanical upgrades or repairs, which means a rooftop replacement is an inspected job even when the new unit lands on the existing curb. Budget the review time instead of assuming a same-week set.

Re-roofing is separately permitted, both overlay and tear-off. That matters more than it sounds. If the membrane is within a few years of replacement, setting a new unit on it means paying for a second crane mobilization and a second permit later, plus flashing work around equipment that just went in. Confirm the roof's remaining life during the site review and decide the sequence once — roof first, then units, or both under one coordinated schedule.

The installation takes a week of your attention. The consequences run fifteen years or more, and they show up in two places: the utility bill and the service contract.

DOE built the case on the operating side. Old, inefficient rooftop units waste an estimated $900 to $3,700 per unit each year, and the high-performance specification DOE challenged manufacturers to hit targeted energy use up to fifty percent below the prior standard. Across the Advanced RTU Campaign, more than two hundred organizations upgraded over forty-three thousand units and cut a combined $37 million a year from their energy bills. On a multi-unit roof, that arithmetic is what decides whether you replace one unit now or budget the whole roof across two seasons.

Most commercial roofs carry more than one unit, and they rarely fail on a convenient schedule. That leaves a choice: replace reactively, one failure at a time, or set a replacement plan across the whole roof and work through it.

DOE's framing favors the plan. Its guidance describes proactive replacement of inefficient, underperforming units as the smarter business move compared with replacement on failure — and even compared with a like-for-like swap at the end of useful service life. The reason is not sentimentality about planning. A planned project lets you specify the equipment you want, negotiate across more than one unit, schedule the crane once, and pull a single permit package instead of three.

Procurement follows the same logic. Equipment availability sits on DOE's own consideration list for a reason: the unit you specified and the unit that can ship in three weeks are not always the same unit. Get lead times in writing next to the price, and decide which substitutions you would accept before you are under pressure to accept one.

If capital is the constraint, phase by condition rather than by age. The unit with the highest run hours and the worst service history goes first, and the rest follow as budget allows.

Two bids on the same roof are only comparable if they answer the same questions. If any of these is missing, ask for it before you compare price.