Gas Pack Replacement: Do You Want Gas on the Roof Again?

The unit on the roof that does both jobs

A gas pack is a packaged unit with a furnace section built into the same cabinet as the air conditioner. One box, one curb, one pair of duct openings; cooling from the compressor, heat from a burner assembly and heat exchanger. Phoenix has a lot of them. Subdivisions built through the 1990s and 2000s in Chandler, Gilbert, Mesa and the West Valley, where gas service was already in the street and builders wanted heat without a furnace closet, put a gas-electric unit on the roof and moved on. Two decades later those units are the ones being replaced, and the replacement raises a question the original builder never had to answer: do you want gas heat up there again?

What changes the scope

Everything in the rooftop unit replacement guide applies here: crane, curb, ducts, roof condition. A gas pack adds its own list.

• Gas piping. The line up the wall and across the roof gets inspected for corrosion, support, a sediment trap and a shutoff at the unit. Black iron exposed to twenty summers of ultraviolet and monsoon rain is not always in good shape, and a new cabinet with a different inlet location may need the run extended.
• Venting and combustion air. Packaged gas heat vents through the cabinet, which is one reason it is simpler than an attic furnace. The flue hood orientation, clearance from the roofline and distance from any fresh-air intake still have to be right, and the new unit's requirements may not match the old placement.
• Heat exchanger age. The exchanger decides whether the old unit is repairable at all. A cracked one is not repaired; the section is replaced or the unit is retired.
• The heat source decision. Gas-electric again, or a packaged heat pump on the same curb? That choice changes the gas line, the electrical load and your utility bills. It gets its own section below.
• Electrical. A gas-electric unit draws less current in heating mode than a heat pump with electric backup strips. If you switch, breaker and wire size are re-examined.

Gas-electric or packaged heat pump

The honest case for gas heat on a Phoenix roof is short. Our heating season runs roughly December through February, with a handful of mornings in the 30s. Gas heat is fast, indifferent to outdoor temperature, and keeps an existing gas account doing something for its monthly base charge.

The honest case for a packaged heat pump is longer. A heat pump in a Valley winter runs in its easiest conditions and rarely sees temperatures where efficiency falls off. It removes combustion from the roof, along with the exchanger inspection and the gas piping. On an APS or SRP time-of-use plan, an all-electric roof simplifies the bill. Incentives for heat pumps exist and change, and the all-electric conversion guide covers the larger question of dropping gas from the house entirely.

There is a third path: a packaged dual-fuel unit, heat pump for mild days and burner for the coldest mornings. For most Phoenix homes that is more machine than the climate asks for, and we will say so rather than sell it.

Where gas packs live in the Valley

Single-story block-and-stucco homes with low-slope roofs. Townhomes with shared roof decks and a row of units lined up like mailboxes. Older Ahwatukee and Tempe tracts where the gas line was run at construction. Manufactured homes sometimes use a ground-set gas pack at the end of the home; if yours sits on a slab, the crane goes away and the scope simplifies, but the gas and venting questions remain.

When to keep what you have

A gas pack with a sound heat exchanger, a working compressor and a refrigerant still in production is a maintenance project, not a replacement. Annual heating maintenance that includes a combustion check and an exchanger inspection tells you where the unit really stands. The repair-vs-replace guide lays out when the math flips. If a technician condemns an exchanger without showing you the evidence, get a second opinion. A crack is visible or measurable, and you are entitled to see it.

Questions to ask any bidder

• Did you inspect the heat exchanger, or are you assuming its condition?
• Will the gas line be pressure-tested and the sediment trap and shutoff brought to code?
• Have you scoped both a gas-electric and a packaged heat pump so I can compare?
• Does the scope include the flue orientation and clearance check for the new cabinet?
• Are the curb adapter and duct transition included?
• Is the number flat-rate before work begins?

Bleuwave scopes both configurations when asked and explains the trade-offs in plain terms. Financing on approved credit is available for either path.

Bring us to the roof

No page can tell you whether your heat exchanger is cracked, whether your gas line passes a pressure test, or whether your curb fits a modern cabinet. Those are site facts. An on-site evaluation walks the roof, tests the gas, runs a load calculation and produces a written scope for each option before anything is ordered.