1. Record what you're seeing
Note the symptom, its timing, and any prior work, and take reasonable precautions if there's a safety concern.
2. Assess the full system
Equipment condition, duct leakage, airflow, humidity, insulation, electrical capacity, and comfort room by room all matter before equipment gets chosen.
3. Get a scope in writing
Preparation, protection, materials, access, permits, testing, cleanup, restoration, exclusions, and change-order terms should all be documented up front.
4. Compare bids on substance
Verify credentials first, then compare what's actually being proposed — not only the bottom line.
5. Check the finish work
Confirm testing, cleanup, paperwork, warranties, and any maintenance that's now the homeowner's responsibility.