I have a 80% gas furnace and a Goodman DSZC16 16 seer heat pump. I live in Eastern Washington.
Our system is currently configured to switch to natural gas somewhere around freezing temp.
However looking over the Goodman literature it seems like switching below freezing would save more money.
I am paying about $1.00 per therm delivered and $0.0731 per kWh.
Check my math on this.
1 Therm x 80% = 80,000 BTU = 80 MBh
$1.00 / 80 = $.0125 per MBh (NG)
DSZC16036 (30 degrees outdoor) = 26.2 MBh, 2.39kW
2.39 kW = $0.174
26.2 MBh (NG) = $0.3275
So even at 30 degrees outside temp the heat pump is significantly cheaper then the gas furnace? Can you run a heat pump when it is below freezing outside? Am I missing something here, too many assumptions?