Why 5°F output can exceed 17°F output
The three figures come from separate tests, and the colder tests can run the compressor faster.
Three temperatures, three tests
The certified data includes heating capacity at 5°F, 17°F, and 47°F. Each figure belongs to an outdoor unit paired with a particular indoor unit, so compare figures from the same pairing.
On variable-speed equipment, the 47°F figure is a nominal rating, measured at the speed the unit's controls would choose at that temperature. The 17°F and 5°F figures are full-speed tests, and the full-speed setting for each temperature is set separately. That is how a colder test can report more heat.
The certified data does not include the compressor speeds, so the figures alone do not show the cause for a particular unit, and they do not describe every condition in a home.
What a share above 100% means
A unit certified for 12,000 Btu/h at 47°F and 13,200 Btu/h at 5°F has a 5°F figure of 110% of its 47°F rating. Tests use different compressor speeds. The ratio compares two tests; it does not measure one setting across temperatures.
A single-stage compressor has one speed. A two-stage unit's full-load ratings use its high stage. The methodology explains the test names and the indoor-airflow exceptions.
For colder design conditions, ask the manufacturer for performance data on the exact pairing, and confirm the house load and backup heat with your contractor.
Where to go next
Compare cold-weather output across the certified data, check a quote's pairing, or estimate a home's heating load.
Test definitions: DOE Appendix M1, sections 3.6.1–3.6.4. Interpolation and chart limits.