Thank you for your question.
The Firefox 8 has a 6-inch flue outlet and so cannot be fitted to a 5-inch flue liner.
Only a Defra approved stove with a 5-inch flue outlet can be fitted to a 5-inch flue liner.
If you are replacing a gas appliance with a solid fuel stove the liner will be a different construction and will not be suitable for for a solid fuel stove.
If you have any questions contact our stove experts on 0845 450 8351
Hope this helps?