Wallpaper79 - My guess is that your brick flue does nothave the required airspace clearances around the flue to combustibles. My 75 year old house in Nova Scotia does not have the airspace needed for wood. Oil and coal flues did not need airspace, modern solid fuel codes demand needs 1 or 2 inches, depending. My WETT installer knew nothing about that requirement, and said WETT didn't teach them about insulating liners. I called WETT, they, of course, say different, and that I in fact need an insulated liner to meet code requirements. In fact, most of the liner systems I've looked at mention the requirement for airspace around the brick flue right on the CSA/UL approval tag.
Bottom line - if you do not have 1 to 2 inches of airspace around your brick chimney, you need an insulated liner to meet code.
The danger is that over the long term, exposure to repeated high heat can increase the risk of fire, especially since your liner is designed to experience 1200F all day, every day. Eventually, at that temp, you will burn your house down. The question was asked in another thread about actual reports of fires when insulation was not used but was required, and the answer was that some manufacturers are getting reports of evidence of excessive heat transfer, but not fires. Wait 10-20 years, and we will be insulating liners at the same rate as we are now replacing old non EPA stoves, except it will be a safety vice efficiency issue.
As for air cooling your flue with vents - likely not a good idea - fire break issues, and usually the space around your flue is a major source air leakage to your attic anyways, so installing a vent is likely going to intoduce more moisture to your attic than give you heat.
To me WETT certification is like any other licence, lots of licensed tradespeople pay no attention to code, rules, safety, or even the laws of physics. Except, it isn't a license, it is a marketing programme that gives some training, and let's you hang a WETT sign out so that you can differentiate yourself from the other guy who didn't bother with the courses. It is voluntary, and you and I could get WETT certification in short order - that wouldn't make us any smarter, just give you better marketing potential IMHO.Lots of folks go to class and pass tests without learning anything.
The general public place these WETT guys on a pedestal, like they can do no wrong, and like what they say would always be right. The guy who told you to cut vents in the wall to cool the flue, after being called because he was WETT certified has just proven to me that he didn't learn anything about code or safety, let alone about keeping the heat in a house, while he sat in the classroom
