What is the preferred material for forge/hood Smoke exhaust pipe?

Hello Blacksmiths:

I am setting my forge up behind my house under a spring porch. The patio below the porch allows room beyond the extend of porch and roof line over-hang for the forge and hood. If I take the pipe stack up twenty feet, I will clear the roof of house by six feet. Now for my question, since I am not going through a roof and the pipe will be 8-10" from the side of house. Do I need to only use stove pipe (8") for the first four feet above the hood and then use the less expensive *"duct" pipe for the remainder?
Or, Should I use the heavier stove pipe all the distance to the top. Or can I use the lass expensive duct pipe for the whole extent? I plan to put a top cap with screen to prevent water coming down the pipe.

Being as our area is very dry, my spouse worries about my forge starting a fire (on the house and/or in the woods) from sparks flying. It seems to me a twenty foot stack would cool off any sparks and provide a good draft?

I plan the use 1"x 1/8" mild steel as straps to hold the stack secure and to attach the stack to side of porch and maintain distance from the house. Then, I will paint the pipe stack forest green to hide it in the trees behind my house.

What is the best material and how high above the forge hood does it need to go?

Thanks for your thoughts!
Houston the Armouror

pipe

What is the siding on the house? Brick- I wouldn't worry. G/P board-
I would, and might consider triple wall. Wouldn't worry about sparks from that stack. BUT......... wouldn't go with less than 10" d.

The house is a ranch style with

Hello Dan and thanks for the advice!
...brick siding around the basement in front and in back. The house is on a hilltop, so the rear basement level patio outside my shop door has a 9 feet 8" height of brick wall on three sides. The spring porch above has a plywood enclosed bottom 9'10" above patio. The stone patio extends out beyond the porch and drip/gutter line. I can place forge outside the porch line, so that forge with hood and the pipe would be 3" from house.

I could use two twenty four inch stove pipe sections and cap it below porch floor. I have 67" of height from top of hood pipe to the porch bottom. So that would be a pipe stack above the hood top, but capped at say 60" and three feet away from porch. I have 15' of a lower stone patio behind the forge.

My wife is worried that moving the forge off the patio in this dry weather will be a fire hazard. I have been married for 21 years and she still does not trust me with fire. I have water-facet nearby and a fire extingisher? I have never burned anything down yet. So, I need some safety advice to assure my continued safety record.

Where do I find 10" diameter pipe in triple wall?
Thank you!
Houston