Type B and Type A vents? 2

[ProcessHVAC]

Dumb quesiton perhaps: my local Gas code calls for Type B vent for Category I appliances, and Type BH or"special venting" for Cat II, III and IV. I have seen some manufactures also mentioning Type A vent required for their appliances which is not mentioned in the Code.

I have no problems specifying and obtaining this from suppliers and manufacturers but, what makes a Type B vent? Double walled steel?

What is a Type A or BH Vent?

 

[IRstuff]

http://www.elitedeals.com/duravent-type-b-vent-pipe.html

http://www.elitedeals.com/duravent-type-b-installation-guide.html

http://www.ehow.com/list_7285461_types-gas-vents-there_.html

TTFN
faq731-376

 

[ProcessHVAC]

So what is a Type A then?

 

[IRstuff]

http://files.engineering.com/getfil...2-bb96d54ebb9a&file=Pick_a_Vent,_Any_Vent.pdf

TTFN
faq731-376

 

[ProcessHVAC]

Thanks, that helps a lot.