I am going to be installing a rivit forge in my little 12x16 shed.  I am going to use a 15 gal barrel for the hood and 8 inch pipe since that is the largest I can find.  The pipe will go up about 4 feet then over about 4 feet and then up over the roof.  My question is will it make much difference if I use two 90 degree elbows or should I use two 45 degree elbows?  I want to get the best draft possible but 90's would be easier for me to work with.  Thanks for any help and suggestions.

yes. a pair of 45 has less resistance than one 90.  also if you cant get 12 inch pipe,  double up 6 sections of the 6 and make it a12.  the 8 is too small.  I hate to see you spend the money and time and not have it work, due to not reading beforehand.

8 inch is not so good. Been there done that.

Here is a good read at this link. http://www.beautifuliron.com/chimneys.htm

 I have purchased some 12 inch 26 gauge spiral duct from a HVAC company that I will be installing soon. I will post some photos when it is complete.

Perry

Thanks for the suggestions.  I am looking forward to seeng photos.  Any ideas for a 12" flashing thru a metal roof?

Two 45 degree angles is a lot more efficient. In many places it is illegal to use 90 degree angles for fireplaces because of the redistance.

http://www.pipebootexpress.com/

Put this in your browser. I have seen phtos of this application doing a search. I have ordered one and will be installing once I get the duct through the metal roof. The silicone boot is rated for 437*F continuous. I have checked temps on other installs and this should be fine.

 

Perry

http://www.pipebootexpress.com/

Put this in your browser. I have seen phtos of this application doing a search. I have ordered one and will be installing once I get the duct through the metal roof. The silicone boot is rated for 437*F continuous. I have checked temps on other installs and this should be fine.

 

Perry

Thanks for the link.  I think that is what I am going to go with.