View Full Version : Need some info from any HVAC guys

Randy Rizzo
08-16-2010, 10:19 PM
Can anyone tell me the difference bertween a Class I and a Class III flue vent? We're putting a Sterling Garage Guy 75BTU heater in a garage. Install manual shows a different size flue pipe for Class I (5") or for a Class III (4"). I'd like to be able to use the 4" but am unsure of exactly what that is. Thanks.

Jim Finn
08-17-2010, 4:48 PM
It has been a few years but I think: class 1 means just single wall flu pipe like 24 guage. Class 2 is double walled vent pipe for gas heaters. (ALuminim and stee)l. Class 3 is suitable for equipment burning wood. Triple walled stainless steel and steel.

Randy Rizzo
08-17-2010, 10:17 PM
Thanks Jim. That was my take on it also, but I couldn't find it spelled out quite as clearly. I planned on using the double wall vent, commonly called "B" class venting. It appears the triple wall vent has gaskets that seal the pipe when it's inserted into the next section as well as a worm drive clamp (radiator hose clamp) to join the pipe sections. It's considerably more expensive also.