Commercial HVAC replacement and installation in Salt Lake City.

The first fork is how the building will heat, because that decides the equipment, the connections, and most of the price. A like-for-like gas-and-electric rooftop replacement is the shortest path: same curb, same gas and power, simplest permit. It also carries forward whatever sizing mistake the old unit had.

A dual-fuel heat pump rooftop unit runs the heat pump through mild hours and hands heating back to the gas burner when it gets cold. It keeps the gas line in service and lowers the risk of a cold-weather capacity gap.

An all-electric or cold-climate heat pump unit removes the gas connection entirely. Heat pump heating efficiency falls as the outdoor temperature falls, and most all-electric and cold-climate units lean on electric resistance heat for the coldest hours. That makes winter heating load, the backup heat strategy, and available electrical capacity the questions that decide whether the switch works on your roof.

Equipment is the line everyone compares. The lines under it are where two quotes for the same tonnage stop matching, so ask each bidder to show them separately.

The nameplate on the old unit records a sizing decision made for a different era of the building — a different tenant, different lighting, different plug loads, a different schedule. Confirming the load against how the space is used today is the step that separates a replacement which fixes the comfort complaints from one that repeats them. Oversizing short-cycles the compressor and leaves humidity and hot spots in place. Undersizing shows up on the first design day of the season.

Efficiency tier is the second decision. DOE finalized a minimum efficiency standard for commercial rooftop units in December 2015, so every new unit clears a federal floor. The real question is how far above that floor to buy. The high-efficiency performance specification that reshaped the market was written to cut unit energy use by up to half, and manufacturers went on to offer more than twenty models that exceed it. With an old unit wasting somewhere between $900 and $3,700 a year, that math is worth running before the order goes in.

Federal guidance is blunt about timing: replacing an inefficient unit on purpose is often the better business move, compared with waiting for failure or with a like-for-like swap at the end of service life. Availability is part of that plan, which is why equipment lead time belongs on the quote right next to the price.

Two buildings on the same block can order the same tonnage and get very different numbers. The unit did not change. The roof, the route to power, the heating choice, and where the crane can park did.

The first visit should end with measurements, not impressions. On the roof: existing curb dimensions, whether the structure beneath can carry the new unit, the condition of the membrane around the opening, service clearances, drainage, and the actual path a crane can take to reach the position. A curb adapter ordered from a guess is a curb adapter that arrives wrong.

Below the roof, federal guidance points at three things that decide whether an equipment option is even available to you: electrical capacity, physical constraints, and the gas line. Confirm the panel, spare breaker space, service size, and what the building already draws. If an all-electric unit is on the table, that check happens before the model is chosen, not after the order is placed.

The operating interview matters just as much. When can the space lose conditioning, and for how long? Who tells the tenants? Does the lot have to stay open? Is temporary cooling needed, or can the outage land on a weekend? Those answers set the crane day, and the crane day is the part of this project everyone in the building actually notices.

Salt Lake City requires a permit for installing or altering a mechanical system, which includes a rooftop unit replacement. The city frames that requirement around safeguarding public safety and protecting life and property, so it is not a step you can work around and settle later. Permit staff work from the Building Permits office at 451 S State St downtown, weekdays from 8 to 5, and can walk an applicant through the submission process.

There is a second step that catches owners out. If the building sits in a historic district or is a legally recognized historic structure, the city directs you to contact Salt Lake City Planning before applying for a building permit. Rooftop equipment is visible equipment, so that conversation belongs early — not after a unit has been ordered.

The first is refrigerant. EPA rules under the Clean Air Act govern how refrigerant is handled and recycled in stationary air conditioning and heat pump equipment, which covers recovery from the unit coming off your roof as much as service on the one going up. New equipment is shipping on newer refrigerants, so a building that replaces units one at a time will run a mixed fleet for years. That is manageable, but it belongs in the service contract and the spare-parts plan rather than being discovered on a hot Friday afternoon.

The second is commissioning. An efficient unit that was never verified is just an expensive unit. Charge, airflow, ventilation controls, and automation settings decide whether the savings on the proposal ever reach the utility bill, and the documentation is what keeps the warranty standing.

Rooftop units condition close to half of all commercial floor space in the country, which means most buildings are not making one replacement decision — they are making a sequence of them. Federal guidance notes the common pattern plainly: facility managers delay a new unit until the old one can no longer hold the space, needs constant service, or fails outright. That delay is expensive in a specific way. Emergency replacement means taking whatever is in stock, at whatever it costs, with no time to run the load calculation or compare heating options.

Planning the sequence changes the terms. When you know which units are oldest and which carry the heaviest load, you can order ahead of the season, standardize on a model your service team already knows, and put the disruptive work on a weekend instead of a Tuesday. The scale version of that idea is well documented: more than 200 organizations working through the federal rooftop campaign upgraded over 43,000 units and cut a combined $37 million a year from their energy bills.

Lifetime cost is the frame that makes the choice obvious. Purchase price is one number, and over the life of the unit it is the smallest one. Energy, service calls, refrigerant, and unplanned downtime are the rest of it.

Ask every bidder to price the same tonnage, the same heating type, the same curb work, and the same crane plan. If one quote excludes structural work or permits and another includes them, the totals are not comparable numbers.