Suppose we assert:
“Whenever fire burns normally, heat is present.”
The direct denial of the whole connected conditional is:
“It is not true that heat must be present in every such case of normal burning fire.”
The negation targets neither the antecedent as a separate fact nor the consequent alone, but the claimed general entailment between them.
Saying merely “The fire is not burning” does not contradict the conditional. The truth of a conditional differs from the actual occurrence of its antecedent now.