As has been pointed out, your forge is a heating type forge. It is made for general iron work and farrier use ( horseshoes). It isn't intended to do HT (and won't do it very well).
Any attempt to HT in that forge will give minimal results at best. If you have to use it, you will have to keep the blade moving all the time, and turn the flame down=n a lot. Read on......
The need to pre-heat any forge that you are attempting to do HT on is because all the refractory has to come up to the temperature you want to have the knife at. In a standard knife forge that will allow a somewhat even heating of the knife blade. In your forge it will be extremely hard to get the refractory evenly heated.
Placing a thermocouple in a forge will read the temperature of the flame. That won't tell you what the blade temp is. Once the forge has been soaked for 10-15 minutes to heat up all the refractory, the TC will be read a more accurate temp if you turn the gas and blower off for a few seconds. It will re-light immediately upon re-starting it. The use of a ceramic TC sheath is how many keep their TC out of the direct flame ( and also extend the life of the TC). IR and laser thermometers are useless for HT.
The best way to get an accurate reading on the blades temp, and to help evenly heat the blade in a forge is to use a muffle ( not a muffler). A muffle is a heavy walled pipe or box that the blade is placed inside. The forge heats the muffle and the muffle heats the blade. This evens things out a lot. If you place your TC inside the muffle, as close to the blade as possible, it will be reading the blade temperature.
A magnet and some practice will allow anyone to HT a 1080/1084 blade with almost any heat source. I will address how to use a forge to HT in. There are only a few things you need to learn to do:
1) Evenly and slowly heat the blade. While running your forge like a jet engine looks and sounds neat, it isn't the environment that you want for HT. Turn down the gas ( and blower if it is controlled) until the forge is a gentler looking glow. Note, many forges can only go so low before they start to sputter and go out. Tune it as low as it smoothly runs, and start from there. The gas pressure will vary, depending on the burner and forge type, but will be much lower than you used for forging.
Here is how to tune your forge and your skills:
Place a piece of 1/8" steel bar stock ( 1080/1084 is good) in it and let it sit for a minute or two. Check it against a strong magnet that you have positioned near the forge door/port. If it is still magnetic, wait a few more minutes. If it is still magnetic after five minutes, turn up the gas ( and blower). Once your forge is running as a temperature that the steel gets to non-magnetic at, you are almost ready to HT. You want the steel to be just about 50-75°F hotter than non-magnetic ( that would be about 1475-1500°F). This is one shade brighter red than the steel was when it just stopped being magnetic. A little practice with the piece of bar stock will get you where you can recognize that color/temp. All this is best done in subdued lighting. Turn off the big overhead lights in a shop, and don't do this in the noonday sun if outside. The colors look best at night with only one 100 watt light bulb burning ( so you can safely see what you are doing).
2) Practice your quenching with the piece of bar stock. Heat it until it stoops being magnetic, and then a little more. Quench in your quenchant ( canola oil works well). Let sit in the oil for one minute and take out. Try to file the edge with a good file. If it slides on the edge like it was on glass, the steel hardened. If it still files, give it a few more strokes, and if it still cuts, the steel was not hot enough to harden. Try again with the steel getting redder color after non-magnetic. You can re-HT the bar of steel many times to practice. Once you have it down where you get a good hardening every time, take the bar and put it in a vise. Break it in half and look at the grain. It should look fine and sparkly....like very fine sand. If it looks big and chunky, the steel was way too hot. Most likely it will be fine grain if you have done the previous steps in getting the forge running right for HT. If you want a comparison, break an old file and look at that grain. Files should have a good HT, and thus fine grain.
3) Place a piece of 2-3" pipe in the forge. It should be stainless pipe or black iron pipe. You don't want galvanized pipe. It will give off all sorts of white smoke that isn't good to breathe and will mess up your forge with white fuzz. If you have a welder, you can weld up a simple 2X3" open end box from pieces of welding steel ( Home Depot steel). This box/pipe will be your muffle. Place it in the forge and let the forge come up to fully soaked heat. That will be about 10-15 minutes running time. Once the inside is glowing (and your quench oil is around 120-130F), you are ready to HT your knife.
4) Place your precious blade in the muffle. Let it heat up until it starts getting red. If you have a thermocouple, place it in the muffle with the blade. Don't just go by the temperature readout. Check the blade with a magnet as it heats up. If the TC is reading accurately, it should read somewhere around 1415°F when the blade becomes non-magnetic. Pull it out as it gets red and Check with the magnet, too. Keep heating redder and checking until it suddenly stops sticking to the magnet. Look at that color ( and your temperature gauge). You want the blade about one shade brighter red than that ( 50-75°F hotter). Stick it back in and heat just a bit higher. Once it gets to where you want it, pull and quench in your oil with one smooth movement. Don't get crazy and try to move too fast, just pull the blade and put immediately in the oil. Let cool for one minute in the oil, and then check with the file to assure the edge hardened. If al is well, wash the blade off and temper in the kitchen stove immediately. The temper should be for two hours at about 400°F and be repeated for a second two hours after cooling the blade off with water.
If the blade wasn't hardened when you check with the file, re-do the HT and make it a little redder at quench.
Following these simple steps...and taking your time....will assure a good HT with even the most primitive equipment. The same use of a magnet and looking at the color in subdued lighting will allow you to use a torch, a charcoal fire, even a gas stovetop flame. Any source of heat that is controllable to some degree can be used to do HT. The results ate hit or miss with the poorer heat sources, but with skill, all that maters ( for 1080/1084) is getting the blade to 1475-1500°F ands quenching it inoil.
