Stuck on a swap? Ask a guy who's been on the roof.

Not always, but assume yes until you prove otherwise. Even same-brand "like-for-like" replacements have changed footprints and supply/return openings over the years, so the old curb rarely lines up perfectly with a new unit.

The move is: pull the old unit's curb dimensions and the internal duct opening locations, then compare against the new unit's submittal. If the openings don't match, you need an adapter — and a good adapter has to transition the duct openings internally, not just sit on top. Measure the existing curb before you order anything. The curb-adapter decision tool and the survey checklist walk you through exactly what to capture.

Sometimes — but never assume it. Many units are field-convertible to propane (LP) with a manufacturer kit: different orifices, a regulator change, and a manifold pressure adjustment. But the kit is unit-specific, it has to be available, and the conversion has to be done and verified, not just ordered.

Confirm the fuel type on the survey, then either spec the unit for LP from the factory or price the conversion kit and the labor as a line item. Getting this wrong scraps the changeout. The survey checklist now asks the fuel-type question up front for exactly this reason.

Matching the old tonnage is a fine starting point, but don't treat it as gospel. The original unit may have been oversized to begin with, and the building's loads can change — added insulation, new windows, a different use for the space, more or fewer people and equipment.

Oversizing causes short-cycling, poor humidity control, and comfort complaints; undersizing leaves you short on a design day. For a replacement, the old size plus a sanity check on the space is usually enough — the tonnage estimator gives you a quick gut-check. For a big space or a change of use, do a real load calc.

Three things, every time. First, voltage and phase — confirm the building's actual supply (208 vs 230, single vs three-phase) matches what you're ordering. Second, MCA and MOCP on the new unit's nameplate versus the existing breaker and wire — a new unit can pull more and force a breaker or conductor change. Third, the disconnect — is it present, the right rating, and within sight of the unit per code?

Capture all of it at the unit, not from memory. The survey checklist has a dedicated electrical section so none of it slips.

Day one, during the survey — not the week of the swap. The crane is often the single biggest cost and the biggest scheduling risk on a rooftop changeout. You need the unit weight, the lift radius and height, where the crane can actually set up, and what it has to clear (power lines, the building itself, parking).

Also check access for getting the old unit down and the new one staged, and whether you need a street permit or lane closure for the crane. Note all of it on the survey checklist while you're standing up there — guessing later is how jobs lose money.