Newbie Build

Hello my name is Andy, but everyone calls me Seddie.

I recently built my own wood stove out of a old fuel barrel. Essentially I built a platform to hold my grates and fire bricks. Installed a barrel wood stove kit for door, dampener and exit flange. I ran 1 1/2 dom tubing front to back through the burn chamber and welded front and back for a heat exchanger. Bent up a box to channel the air from a squirrel cage fan through the tubes.

It works ok most of the time, really hard to keep it up to temp unless its packed full of wood. Even then it kind of peters out every now and again. It also smokes through the door unless damper is wide open. I have a 6" chimney through the wall then vertical outside about 4' above roof line. I've added a additional intake opening 2" x 6" to try and help the burn drawing air up through the ashtray area.

Questions:
How do I determine the correct intake size?

Will it hurt to make my chimney taller? Is there a thing as too tall?

Plan to use 1 x 1 box tube manifold  to add a secondary burner.  Will that be big enough?

Will adding a deflector plate below the pipes help it holding temp?

Any help would be greatly appreciated in helping me dial this guy in. Right now I have like $150 bucks in materials, most were salvaged parts or scrap.

First off nice build.
I'll assume you are using well seasoned wood as a start. What comes to mind is your large steel tank is robbing too much heat and stunting your draft. I would start by adding a section of chimney but that won't help with your turn down ratio. Next would be to insulate your firebox up to the tubes. If it was me I would fire brick the whole bottom third. If I wanted to test that theory on the cheap I would cut up a 50 gallon barrel and lay it ridges down under your grate to create an insulating jacket around the fire the ridges will give you a 3/4 inch air gapl. Cut the largest section of curve that will fit through the door and bolt two sections together if necessary. You want to raise the fire's temperature to get a clean burn before you start drawing heat from it. As an added bonus it will act as a sacrificial liner to protect you main tank from corrosion from the fire.
My two cents.
Cheers,  David Baillie  

I think David has the core issue right. With such a large and uninsulated cavity, heat escapes before building up to full combustion temperature. I would advise lining with firebrick all the way up to the bottom of the heat exchanger tubes, and putting in a "ceiling" to keep the combustion zone below those. A secondary combustion zone with air supply could go below this first separator. My first approach would be to have a gap in the primary zone ceiling at the back, and in the secondary zone ceiling at the front, so hot gases flow up in back, forward through the secondary zone, then up and back toward the chimney in the heat exchanger zone.

If cost is a major issue, I like the idea of a sacrificial barrel liner; I would fill between the layers with something a bit insulating and some mass, like a 2" layer of cob (clay soil with lots of sand worked in). This would hold heat, protect the outer shell, and with firing would become water-resistant and stable even after the inner liner starts to rust out.

Taller chimney = more draft, Taller larger diameter = better draft yet.  (Smaller diameter = faster airstream but even more length is needed to equal the volume of the larger pipe.
Small door means difficulty stoking the stove to capacity.
+1 on firebrick it for longevity but,..... firebrick will slow down heat transfer, it will radiate heat longer, but less of it for a given time span.
A tall grate has a tendency to let air simply pass under the fire and directly up the chimney without greatly encouraging the fire, many people have better fortune with a simple bed of ash and the air inlet blowing directly on the wood mass.
A short mass of wood rather than sticks that fill to 90% of the length of the stove promotes inefficiency, and alternative airflow rather than through the body of flames.
Finally a "double pass" design with a baffle plate between the fire and the heat exchange tubes ( pass from the fire box to the exchanger at the front (passes the smoke back over the flames) and chimney at the back) would probably increase overall efficiency with the caveat the draft must be stronger yet to keep smoke from escaping.