Under what conditions would I need a "fan in a can" for this unit to work properly? Do I need to re-line my old chimney (interior location, clay lined)?
You would need a "Fan in a Can" or other power exhaust system if your chimney is not suitable for use with the IN7 boiler in your inquiry. You will need to have a on-site professional inspect your existing chimney to determine if it is appropriate and if any repairs/updates are needed.