I used these to spec and design my flue fluesupplies.com
It came in at just under £700 for the complete flue system, running through the loft in a bungalow.
It is being fitted by my builders but I have a major problem as my Building Control will not sign it off. I was complaining about that on an earlier thread. It is being installed as per the appropriate building regs, pretty straight forward. The hardest part is getting the flashing and roof modifications good and weathertight.
The problem with no sign off may become an issue when I come to sell or if my house burn do. However, the building officer has left me in an impossible position. Basically builders on site, hole in my roof where an old chimney was and flue in my hallway.
The HETAS installers were quoting some ridiculous prices and I have heard some horror stories.