How many vent details?

I have a hard time remembering (learning) vent details such as where type B vents are appropriate and where Type L vents will do. According to the standards it appears that all Im really responsible for is turning up the thermostat and see if the heat source functions. But I would like to get straight in my little brain …B i can understand is only for nat gas or propane but only on ‘listed’ units…what does that mean? Looks like “L” accomodates hotter fires, is this adequte for wood fires? Am i asking for trouble even going there? basically everything I run into around here is plastic for comb air and vent (high E heating units) but I would like to know something about the metal. Ive checked all over including the Type B & L stuff right here at good old internachi but theres too many details…unless I making too big an issue since I dont understand them. input from americas finest please
mike in MN

I hear where ya coming from. Figured I wouldnt get too crazy over types outside B and L. Then the other day i have a zero clearance built in wood burning fireplace with a double wall vent thru a chase ‘chimney’. And this unit can be used also for gas. Choice is yours the mfg said. So what type of vent does this darn thing have?? Confuses me. I just call it double wall vent Hopefully when you get some responses , it will help me and probably others to understand it.

Type B is a double wall pipe, the walls are about 1/4" thick. The inner lining is aluminum. Listed means UL or CSA gas appliances and can only be used for gas fired appliances, keeping it simple that would be a furnace gas space heater or a water heater. Type BW is a special type of B vent that fits inside a stud cavity 3.5 X 14.5". Type B vent needs to have 1" clearance from combustible materials.

Type L looks very similar to type B but is rated for higher temps. It can only be used on certain types of appliances that have a relatively low exhaust temperature but higher than a gas appliance, such as wood pellet stove. Someone needs to help me out with other type L appliances, cause we don’t see that stuff in the land where natural gas is king and the nearest tree is a five hour drive. You could also use type L for an appliance that requires type B provided the size, inside diameter, is correct for the installation. Type L needs 1" clearance from combustibles.

Next we have type A, for solid fuel, double wall, the walls are one inch thick, and the inner liner is stainless steel and often the outer liner is too, but not necessarily. Type A can be used for traditional solid fuel, wood, coal, and oil, stuff that would otherwise require a masonry chimney, like maybe a gas fired incinerator. Type A typically is much larger than a B or L, 8" or more. A vent clearances are typically no more than 1" and maybe less, depending on the manufacturer.

Single wall pipe is sometimes called Type C, it is mostly used for connecting an appliance to a chimney or one of the double wall manufactured vent above. Thickness of the metal, whether it is welded or slipped together will depend on the fuel and expected exhaust temperatures, Clearances for type C will range from 6" for a gas appliance connected to a B vent to as much as 18" for an incinerator. Shields made of metal or asbestos, koff koff, may be used to reduce clearances for type C.

Eventually gas venting will go the way of knob and tube wiring, as appliances are replaced by manufacturer supplied direct vents or high efficiency appliances that cool exhaust gases so low they can use plastic piping to shoot the exhaust out the side of the house instead of up a chimney.

The use of forced draft appliances, a fan that blows exhaust out instead of relying on hot air rising, also means that you may see some ‘chimneys’ sticking out the side of a house or garage. Approach these with caution, and talk to the local AHJ before you say anything about these.

Erik…perfect…exactly what I was wanting thanks so much. Just one more inquiry if you will; why be cautious concerning pipes out the side? that just tells me right off the bat that i have a high efficiency heating unit and it will more than likely be pretty trouble free and i report combustion air and vent are plastic and cant really inspect the exchanger and theres nothing slapping me in the face we’re good (providing theres no funky stuff or super long runs or etc). so what are you referring to there?
and again thanks for the concise metal pipe info, its just what i needed
mike in MN

You are responsible for the heating system as a complete system not just operating the thermostat. The pic below is from just today, single wall flue in the attic combined WH and furnace don’t you think that could bite your Butt to miss something like this as its a little hard to see in the attic from the thermostat;-)

That was better than taking a class. Thanks

I was referring to an ordinary B or L vent sticking out the side of a garage, which I have seen and looks odd, but is apparently OK in some places, but while we are on the plastic pipe topics, there are many things to watch, such as they need to grade back to the furnace, so that water runs back to the furnace and the condensate line, not so the water runs out the end. They need to be installed above the ‘maximum snow line’ for your area. I see sometimes they get all iced up to the point they are blocked, expect to see some rule changes as they become more common. Codes are slow to update, so your primary source of information is the manufacturer who made the furnace. Go to the furnace manufacturer web site and download the installation instructions for the model you inspected.

this was all superb input - you guys rock