The answer to 'how much to replace boiler in Illinois' is that the cost can vary significantly depending on several factors. Generally, you can expect to pay between $3,000 to $10,000 or more to replace a boiler in Illinois.
The exact cost will depend on the size and efficiency of the new boiler, the complexity of the installation, the cost of labor in your local area, and whether any additional work is required like upgrading the venting or plumbing. Older homes may also need asbestos abatement which can add several thousand dollars to the project. It's best to get multiple quotes from licensed HVAC contractors in your local area to get an accurate estimate for your specific home.