Heat-Pump Sizing for a 2,400 sq ft Johns Creek Home: An Honest Walkthrough

The honest sizing walkthrough we use on every estimate

This is the same diagnostic we walk through with a Johns Creek homeowner during an in-home estimate. The home: a 2,400 sq ft two-story built in 2002, average insulation, double-pane windows, attached garage, vented attic. The goal: replace the failing 4-ton single-stage AC + 80% gas furnace with a heat-pump-based system.

Step 1 — Manual J (load calculation)

Using ACCA Manual J inputs (orientation, window U-values, infiltration rate, occupancy), the cooling load lands at 2.9 tons and the heating load at 54,000 BTU/hr at the 17 °F design temperature. The old 4-ton AC was oversized by ~38% — which explains the short-cycling and humidity complaints we heard during the consult.

Step 2 — Equipment selection

We recommend a Trane XV18 3-ton heat pump paired with the existing 80% furnace as a dual-fuel system: the heat pump handles cooling + heating down to about 35 °F, the gas furnace takes over below that. This combination beats heat-pump-only in our climate because Atlanta hits the teens 4–8 nights a year, and the gas furnace's $0.95/therm operating cost is cheaper than electric resistance backup at those temperatures.

Step 3 — The cost math

• Equipment + install (Trane XV18 + thermostat + dual-fuel control + 10-year parts warranty): list price varies by promotion + financing terms — we'll write the actual number on the estimate.
• 25C federal tax credit: $2,000 off (heat pump qualifies through 2032).
• Georgia Power rebate: varies — we'll check the current Marketplace schedule before we write the estimate.
• Trane factory promotion: available most quarters — we apply the current one automatically.

Net out-of-pocket after credit + rebate is meaningfully less than the sticker price. We never bury those numbers — they're on the estimate in plain English.

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