Propane forge not hot enough | Problem Solving | Forum

Kind of a shot in the dark here as I am quite new. But seeing as heat travels upwards you are probably losing an awful lot of your heat through those vertical vents. I would try putting a soft heat brick over them.

You also might try forcing more air into the furnace via a blower rather than just using negative pressure.

Emphasis on me being really new and by no means a professional. 

Definitly plug the holes on top.  Also if the interior is made of hard firebrick, they are massive heat sinks and will take up to 30-45 minutes at least to get up to temp. and will slow down any high heat from happening for a while.  If this was as you say a brass furnace 1)   Brass melts at a much lower temp. than steel welds at, and they may not have built it to specs. that we would want as far as refractory mtls.  2)  If it was a brass furnace, give up hope for welding in it as it is probably contaminated with copper, one of the sure ways to NOT get a decent weld. Relining it will remove or seal up any contamination.  You may want to reline it with Kaowool buttered with hi temp mortar for the sides and top, and castable refractory cement for the bottom and an inch or so up the sides to resist flux, as flus will eat up kaowoll like water on cotton candy.  As far as the door goes, remove it and set up a brick shelf and a system of hard firebricks to allow you to adjust your door to the size of stock you want to push in.  This will minimize the heat exausting out of the forge.  Venturi burners can weld if designed well, and on these Ron Reil burners you might make a disk with a tab for screwing over the large air inlets so that you can throttle back the cold air coming in as this further cools the forge down.  All air, other than needed for combustion, will cool down your forge.  Try covering one of these holes a bit with tin foil and opening it a little at a time until you get good combustion on that burner.  this will give you an idea of the ideal fuel air mix for your burners.  Just about every forge needs some tuning for optimal efficiency.  Think of a tin can lid big enough to completely block the air inlet of the burner and add two tabs opposite of each other.  Bend one up at 90 degrees for a handle for adjustment, and drill the other and the opening of the bell reducer with a small drill and tap for a screw and washer for a pivot to allow you to pivot it to throttle the in coming air flow into each burner.