CSLB C-20 HVAC ContractorHeating SystemsHard
A heat pump system has a balance point of 30°F. On a day when outdoor temperature drops to 20°F, what happens to meet the building's heating load?
- AAuxiliary (supplemental) electric heat strips engage to assist the heat pump
- BThe outdoor fan motor reverses direction to increase airflow
- CThe reversing valve locks in cooling mode
- DThe compressor shuts off completely and only auxiliary heat runs
Show answer & explanationAnswer & explanation
Correct answer: A. Auxiliary (supplemental) electric heat strips engage to assist the heat pump
Below the balance point, the heat pump's capacity alone cannot offset the building's heat loss, so supplemental electric resistance heat strips (or a secondary heat source) energize to make up the difference while the heat pump continues operating.
Why the other options are wrong
- B. Outdoor fan motors do not reverse direction to increase capacity.
- C. The reversing valve stays in heating mode; it only switches for defrost.
- D. The heat pump typically continues running alongside auxiliary heat, not shutting off, unless it's an emergency heat call.
Balance Point & Auxiliary Heat
The outdoor temperature at which a heat pump's output equals the building's heat loss; below this point, supplemental heat is needed to maintain comfort.
- Below balance point, heat pump capacity declines with dropping outdoor temp
- Auxiliary heat (electric strips or gas furnace) supplements, not replaces, the heat pump
- Emergency heat mode is a manual override that uses only auxiliary heat
Memory trick: Below the balance, call for backup — strips join in when it's cold enough to hiccup.