Marietta, GA: the heat pump payback math
In Marietta, the math is close enough that it comes down to how long you plan to stay. $3,500 is what Marietta would pay extra to go electric rather than replace the furnace and AC with the same again, once the $2,000 federal credit is applied. Marietta's residents would see roughly $341 a year back in running costs, putting the payback around 10.3 years. Whether that's worth it in Marietta depends on how many years you expect to own the place.
The climate behind Marietta's payback figure
Marietta has a mild winter by US standards — 2337 heating degree days a year against a 65°F base — and summers are hot enough that cooling matters as much as heating, at 2091 cooling degree days. 12.7°F is the figure equipment gets sized against here — the 99th-percentile cold snap, not an average day — with a record low of 11.3°F on file. Worked through the model, that's a seasonal COP of 3 on the cold-climate unit fit for this climate. Marietta needs the cold-climate class of unit: past a 25°F design temperature a standard heat pump falls back on resistance backup often enough to eat the savings. These numbers come from DOBBINS AIR RESERVE BASE AIRP, the closest NOAA station, 2.9 miles out.
The month-to-month numbers for Marietta
A 2000-square-foot house here would pull roughly 1,973 heating kilowatt-hours annually on top of cooling, totalling about $560 a year on electricity. That compares with roughly 24 Mcf a year of gas at Marietta's 20.42 per-Mcf rate — about $901 a year — against a local electricity rate of 14.90¢/kWh. Priced as a standalone purchase rather than against a like-for-like replacement, equipment payback runs about 39.6 years, for a 15-year net position $1,618 ahead.
If your home heats with electric baseboard instead of gas
Gas isn't universal in Marietta — many houses run on electric heat already. Swap the comparison to resistance heat instead of gas, and Marietta's answer improves. The saving here runs about $726 a year, which recovers the extra $8,000 spent going electric in roughly 11 years.
Where Marietta ranks in this dataset
Among 3206 cities, Marietta's winter puts it at rank 2262 for severity, while its size puts it at rank 625 for population — 1 in both cases being the extreme. That's the mildest third of cities covered, where utility rates carry more of the answer than climate does.
Deciding what's next in Marietta, GA
About 63,122 people live in Marietta, Georgia, and every number on this page is what a contractor would actually work from when quoting a system here — the point isn't to replace that quote, it's to tell you whether to bother asking for one. Here, there's no cost penalty to waiting until your current furnace or AC actually needs replacing.
Ask a local HVAC contractor for a quote before committing either way.
Reading further on this page's numbers
The methodology guide walks through exactly how Marietta's 3 seasonal COP and the rest of this page's numbers get built. Marietta's 12.7°F design temperature falls on the cold side of the 25°F cutoff the cold-climate unit guide walks through.