The answer to 'how much to replace HVAC system in Illinois' is that the cost can vary widely depending on several factors. Typically, a full HVAC system replacement in Illinois can range from $4,000 to $15,000 or more, with the average being around $8,000 to $12,000.
The exact cost will depend on the size of your home, the efficiency rating of the new system, the brand and model you choose, any necessary ductwork modifications, and the complexity of the installation. Additionally, the cost can be influenced by your location within Illinois, as labor and material prices can vary by region. It's essential to get multiple quotes from local HVAC contractors to ensure you get the best value for your specific needs.