You need four main items:
Self explanatory but best 5kW selection here
If you are employing an installer then the above is all you will likely require as your installer will usually want to provide the rest. If proceeding down the DIY route then you will also need the two items below:
1x Chimney Liner Fitting pack
All you need once you have the stove and liner
Please see our infographic about the most appropriate fitting pack
If your stove is 5" collar and DEFRA approved (covers most stoves) choose a 5" stove to 5" liner fitting pack.
If your stove is 5" collar and NOT DEFRA approved choose a 5" stove to 6" liner fitting pack.
If stove is 6" collar choose a 6" fitting pack.
If your stove is 4" collar and stove is DEFRA-approved choose a 4" stove to 5" liner fitting pack.
1x Closure Plate
Seals off the chimney above your stove - or make your own from 12mm Hardiebacker board
More info and buy here
With the above four products - that is everything you need except a few tools.