Quick answer
- Every replacement starts with a Manual J load calculation — never sized by what's already there.
- Quote should include AHRI certificate, model numbers, SEER2 ratings, and refrigerant type.
- Install day: old equipment out, new equipment in, line-set evaluated (replaced when refrigerant changes), refrigerant charged by weight not gauges.
- Commissioning includes static pressure measurement, airflow verification, and refrigerant subcooling/superheat checks.
- Manufacturer programs (Trane Comfort Specialist, Carrier Factory Authorized, Rheem Pro Partner) can mean extra training and stronger labor warranties — verify any dealer's status on the manufacturer's own locator.
Before the quote — the in-home load calc
A real replacement starts with a Manual J load calculation. That means a tech walks the house with a tape measure, counts windows, identifies insulation type, notes orientation and shade, and runs the numbers. The result is a BTU/hr cooling load and a BTU/hr heating load for your specific house.
If a contractor offers a quote without doing any of that — sizing 'in-kind' from what's already there — they're guessing. The current equipment might be oversized (most are) or undersized. Either way, replacing in-kind perpetuates the mistake for another 15 years.
Reading the quote
A complete replacement quote should include all of the following. Anything missing is a red flag.
- Manufacturer and model numbers for the outdoor unit, indoor unit, and air handler/furnace.
- AHRI certificate number (verifiable at ahridirectory.org) — proves the matched system meets the rated efficiency.
- SEER2 rating, HSPF2 rating (for heat pumps), AFUE rating (for gas furnaces).
- Refrigerant type (R-410A on existing-stock equipment, R-454B on most 2025+ equipment).
- Manufacturer warranty terms (typically 10-year parts) AND the contractor labor warranty.
- Line work scope: replace the line set? Flush it? Test for leaks?
- Electrical, condensate, and structural changes (new disconnect, drain pan modifications, pad replacement).
- Itemized total with no 'TBD' line items.
Install day — what good looks like
A typical residential replacement is a one-day install with 2-3 technicians. Old equipment comes out first (recovered refrigerant in EPA-approved containers, not vented). New outdoor unit is set on a pad or stand. Indoor air handler or furnace is set, and electrical, refrigerant lines, and condensate are reconnected.
The line set (the copper refrigerant lines between outside and inside) gets evaluated. If you're switching refrigerants (e.g. R-410A → R-454B), the line set has to be either properly flushed of old oils or replaced — the two refrigerants and their oils aren't compatible.
Commissioning — the part that gets skipped
Commissioning is the post-install verification that proves the system is operating as designed. It's not the same as 'we turned it on and the air felt cold'. A proper commission includes:
- Static pressure measurement at the air handler (should match the spec sheet).
- Airflow verification per zone (with a balometer or duct traverse).
- Refrigerant charge verified by superheat / subcooling — not 'beer-can cold' on the suction line.
- Thermostat configuration confirmed (single-stage vs two-stage vs variable-speed control signals).
- Condensate drain verified flowing and trap is wet.
What manufacturer dealer programs actually mean
Trane Comfort Specialist, Carrier Factory Authorized Dealer, and Rheem Pro Partner are manufacturer-direct programs. They require ongoing training, customer satisfaction tracking, and warranty performance. They can also unlock stronger warranty terms (sometimes 10-year parts AND labor instead of 10/1) and faster manufacturer support when something does go wrong.
If a program tier matters to you, verify a contractor's current status directly on the manufacturer's dealer locator (trane.com, carrier.com, rheem.com) rather than taking a website's word for it. What matters most day-to-day, though, is the load calc, the commissioning, and the labor warranty in writing.
We're a family-owned Lowcountry company (All Star Heating & Air, in business since 1993) that installs and services Carrier, Trane, Rheem, and other leading brands — so we can specify the right equipment for your house rather than pushing a single line.
Have a question about your system?
Talk to a real Charleston Lowcountry technician — a family-owned team with 30+ years of local experience that installs and services Carrier, Trane, Rheem, and more.