What is the theory behind the switch from B-vent to only using stainless single wall for horizontal venting power vent heaters. It looks to me that the B-vent would be more fireproof with a thimble and the clearances used with B-vent. The only issue I can think of would be moisture resistance for the stainless. I guess prior to a couple of years ago the B-vent was OK.
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Class III venting
- Thread starter copo69
- Start date
manwithtools
ALLIANCE MEMBER
I think it's centered around corrosion resistance of the stainless. The B-vent could rust through the inner layer and it would not be visible to the casual observer. Once rusted through the inner wall you now have a single wall pipe - until the outer pipe rusts too.
Motor2Wheel
Member
Thanks Man, I believe you are correct from what I have been searching here:
http://www.duravent.com/docs/product/L915_W.pdf
I thought it had to do with the seals between joints, but I believe it is corrosion resistance.
I just used B-vent on a new installation and will make a note to disassemble to inspect at the end of the season, like normal maintenance. It should be pretty easy for my application. (See other thread on Hot Dawg install)
http://www.duravent.com/docs/product/L915_W.pdf
I thought it had to do with the seals between joints, but I believe it is corrosion resistance.
I just used B-vent on a new installation and will make a note to disassemble to inspect at the end of the season, like normal maintenance. It should be pretty easy for my application. (See other thread on Hot Dawg install)
B vent is specifically approved for Category I appliances as regulated by the Nat'l Fuel Gas Code, NFPA54. As such it is for Non-condensing negative pressure vent systems. Stack temp must be 140* above the dew point temp in Cat I.
Cat III is positive pressure, Non condensing, corrosion resistant, 140* above dew point.
The difference is positive/negative pressure. When these Categories were developed an introduced in '92 many furnace manuf gave the option of buying one unit and having it approved for either vertical or horizontal venting, in other words Cat I or III. They quickly found out that the same fan was not going to be happy doing both jobs and pretty much all of them went with either Cat I or Cat III in the non-condensing products. As efficiencies of appliances have increased, B-vent becomes...much shorter lived as opposed to SS. Also, you cannot be blowing flue gases out of the joints of Cat III and you can in I. SS is better and safer.
Cat III is positive pressure, Non condensing, corrosion resistant, 140* above dew point.
The difference is positive/negative pressure. When these Categories were developed an introduced in '92 many furnace manuf gave the option of buying one unit and having it approved for either vertical or horizontal venting, in other words Cat I or III. They quickly found out that the same fan was not going to be happy doing both jobs and pretty much all of them went with either Cat I or Cat III in the non-condensing products. As efficiencies of appliances have increased, B-vent becomes...much shorter lived as opposed to SS. Also, you cannot be blowing flue gases out of the joints of Cat III and you can in I. SS is better and safer.
Motor2Wheel
Member
Lesson learned.... I'm going to upgrade to Cat III. Thanks for the input.
manwithtools
ALLIANCE MEMBER
Here's a source I found that seems to have reasonable prices on Cat III piping.
http://www.houseneeds.com/heating/venting-pipe-heating-boilers-water-heaters/novavent-z-flex-z-vent-4-inch-stainless-steel-cat-3
No affiliation other than having bought from them and received items quickly and for what I thought was a good price.
http://www.houseneeds.com/heating/venting-pipe-heating-boilers-water-heaters/novavent-z-flex-z-vent-4-inch-stainless-steel-cat-3
No affiliation other than having bought from them and received items quickly and for what I thought was a good price.
Motor2Wheel
Member
Thanks, Man, for the link. I checked it out and looks good. Here's my new dilemma:
I was hoping to replace the B-vent with the SS directly, in other words, use the same thimble and not have to replace any of the work I had already done in that area. This might not be the case now.
Can you offer some answers to these questions?
1. Is the CAT III 4" the same O.D. as B-vent?
2. It almost appears like the CAT III pipes are single wall, is this true?
3. What is the difference in heat dissipation to ambient between the both?
4. Is an adjustable Elbow available with CAT III, like B?
Thanks for all the help.
I was hoping to replace the B-vent with the SS directly, in other words, use the same thimble and not have to replace any of the work I had already done in that area. This might not be the case now.
Can you offer some answers to these questions?
1. Is the CAT III 4" the same O.D. as B-vent?
2. It almost appears like the CAT III pipes are single wall, is this true?
3. What is the difference in heat dissipation to ambient between the both?
4. Is an adjustable Elbow available with CAT III, like B?
Thanks for all the help.
I am not a plumber so take this advice for what it's worth, however I did install my vent pipe for my Modine hot dawg.
1. I can't answer that for sure.
2. Cat III is in fact single wall, joined by an included silicone gasket and hose clamp.
3. Cat III will be hotter to the touch is that's what you are asking.
4. You can cut Cat III pipe any length you want, you just need to clean up the burrs before inserting it into the gasket.
Even if the thimbles are the same size I would not try to use B in place of Z, it will be against code and it presents warranty, and liability issues.
1. I can't answer that for sure.
2. Cat III is in fact single wall, joined by an included silicone gasket and hose clamp.
3. Cat III will be hotter to the touch is that's what you are asking.
4. You can cut Cat III pipe any length you want, you just need to clean up the burrs before inserting it into the gasket.
Even if the thimbles are the same size I would not try to use B in place of Z, it will be against code and it presents warranty, and liability issues.
SuperD
Well-known member
Category III is made both in single wall and double wall. In Canada the clearances for the Category III are much like the B vent, 6 inch for single wall and 1 inch for the double wall. The joints must be sealed, some systems are equipped with a high temperature gasket that requires a silicone grease to be used to ensure the pipe slides in without damaging the seal. They also make adjustable lengths, and some of the single wall is designed to be cut to length. The double wall is very expensive, but with a stainless steel liner it should last a very long time.