UL-103 vs UL-127

UL 103 and UL 127 both state "...are intended for installation in accordance with the Standard for Chimneys, Fireplaces, Vents, and Solid-Fuel Burning Appliances, NFPA 211." An UL 103 listing only covers the chimney, whereas an UL 127 listing covers factory-built fireplaces, including the fire chamber, chimney, roof assembly, and other related parts that are entirely factory-made and that are intended for unit assembly in the field. HeatnGlo manufactures their own chimneys, so they got UL 127 listing, if you buy a Metal-Fab, Simpson Duravent, Selkirk Metalbestos, etc. chimney it will be listed to UL 103HT. When testing for both UL 103 and UL 127 the manufacturer has the option of testing to 1700°F or 2100ºF. If they test to UL 103HT they are telling you that they tested to 2100ºF (HT for High Temp). You could pretty safely assume that if a company is calling their pipe HT they mean "listed it to UL 103HT", but you should never assume, so check to see if it is listed.

No wood stove can be connected to a prefab chimney not rated for 1800 degrees. UL127 is 1700 degrees so no wodstove can use that vent setup. However if the installer used HT 103 2100 vent pipe then that pipe can be used because 2100 degrees is higher than 1800. That takes care of the venting issue unless the cross-secional are code applies. In which you may be required a liner
Since most Pre fabs are only tested for that purpose the insert has to be listed for prefab installation

I new somthing was up last week when you posted that your SL300 chimney was rated to 2100*. I ment to call heatilator, and this morning i did. Its 1700*. it will need a reline and insulation. No direct connect no mater what the cross sectioal is. Strange that there EPA fireplace the 7100 is listed to run on that pipe, because its much the same as a large woodstove. But the proof is in the details. Jotul requires 2100* pipe, and there is only one way to get that. A liner and insulation. If you dont follow the rules, your risk your insurance,and your inspection failing.

No, you cant run double wall down there. It will condensate between the layers. Double wall chimney will be at least a 8" od anyway. You need to use 1/4" insulation wrap and a 6" liner. It will be a tight fit in a 8" flue. I would call the pros in. That will not be a fun install.

DIY, $300-500 for liner $200-300 for insulation wrap. Double it if you have a pro do it.

From what metal says, I gleam that a maker could easily test to BOTH 127 and 103 (either reg or HT). The idea being that 127 is the whole unit test and 103 confirms the chimney.

Amazingly enough, earlier posts here have shown that manual state certain inserts can be installed into prefabs WITHOUT new liners is the prefab is newer - because many have been tested to 103 HT (2100) and that is OK.

But, in the real world, since most pre-fabs are not compliant....we suggest relining. Whether insulation is needed is yet another question and again depends on the listing of the existing and the manual for the insert.

I am curious, can you vent a woodstove into a prefab chimney/ firebox. My situation is a new Hearthstone Heritage rear vent (sitting on hearth) into a Preway Chimney rated 8A (exisiting). I was thinking of running a flex liner up the existing 8" pipe to reduce to the needed 6" with a TEE cleanout. What is the PROs opinion on such an istallation? My old woodstove was vented thur a deadfront of the zero clearance fireplace which was an even worse scenario. Any help is greatly appreciated.