Just as an interesting aside here, perhaps we have some good engineers on board.......let's see how good.....
Assume a 6" round pipe, which can only at most contact an inner ceramic tile liner for a very small area. Now, take the interior of the said 6" round pipe up to 1000 degrees on a constant basis - for purposes of this, let's assume the OUTSIDE of the pipe is 1000 degrees.
Given that small point of contact and 5" of masonry (tile liner plus 4"), what is the maximum temperature that will be generated along a surfact at the outside of the masonry?
Of course, it is virtually impossible to sustain pipe temps of 1000 degrees, and UL tests also take short burst of higher INTERIOR temps into account, but these bursts are not long enough to heat though masonry to any degree.
The strange thing is, said fireplace is perfectly legal to be used as is with tile liner as inspected, built and approved by local officials......
Here's another theoretical - line tile lined 12x12 chimney with 6" pipe that has spacers which prevent it from touching tile liner. Assume at least 1" space. What would be the maximum temp reached at the outside of the masonry?
My experience tells me in both cases it would be vastly less than the combustion point of wood, and in the second case I doubt it would ever reach even 50 degrees over ambient with normal use.
The above is for discussions sake only.....obviously we will never sort out all those instructions and codes......
Just FYI, radiant heat transfers according to the surface area in sq inches or feet which directly faces the receiving object. When either object (source or target) is round or on an angle, the radiant heat is vastly reduced. Again, hopefully we can get an engineer to chime in.
Yes, I think that manufacturers should test these liners in various chimney types (lined, unlined, etc.), but consider a couple factors:
1. Most manufacturers test in-house and ONLY to pass the current standard. In other words, they do not even send pipe to UL, just test results.
2. Manufacturers also like to sell insulation.
It is also a mistake to think of any code as the be-all, end-all of knowledge. Codes are constantly updated and influenced by manufacturers, trade groups, etc. ---- The same codes told us to do it a different way years ago - at a time when the stoves were much more dangerous and ran constantly higher flue temps.
Another comment which can show how little testing the manufacturers must do - Homesaver for instance make liners that are round, square, rectangular and oval. They make sizes from 4 inch to 16" and bigger. OK, so are you going to tell me that a 6" liner in a 12x12 gets anywhere near as hot as a 10" SQUARE liner in the same chimney. Let's do the math - one has an outside area of about 480 square inches per foot and the other one has 75 square inches. Also, one is almost up against the tile and has flat sides! One has large areas radiating directly to the flat surfaces, and other other is round. Even without any engineering experience, I can guess that the radiant effect of the square liner on the combustibles outside (given the same surface temp of the metal) has to be by a factor of 10 or more!
This, if nothing else, shows the folly in current testing or lack thereof. My guess is the Homesaver and others will not give you straight answers to concerns such as these.