Most residential heating systems have a capacity of

HVAC, which stands for Heating, Ventilation and Air Conditioning, is very useful in countries with 4 seasons. During summer, they use air conditioning; during winter, they use heat pumps. The capacity of HVACs are usually expressed in tons. 1 ton is equal to 12,000 BTU/h. For residential heating systems, the capacity usually ranges from 1-5 tons.

Ithink the answer is d.