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aze

I have a Steinel HG 3210 Heat gun, and I decided to take some measurements of how accurate the LCD temperature display is.

I used a cooking thermometer with a corded probe and LCD display, which had a max temp of about 385 degrees. I have two of the same thermometers, and they read about 1 degree apart so I trust the thermometer. I put the probe inside the vriptech large jetflo stem, so that the temperature sensor tip was located about 1 cm above the screen, right where the herb would go. This required me to cut a small hole in the screen for the probe to feed through.

In this table, the first number is the setting on the heatgun LCD, then the measured temperature, and then the difference.

Heatgun temp, Measured temp, difference:
200 183 17
220 201 19
240 216 24
260 232 28
280 250 30
300 268 32
320 288 32
340 298 42
360 315 45
380 334 46
400 350 50

I didn't read higher than that because my thermometer wouldn't be reliable at higher temps. These measurements are after the heat gun has been turned on, with the intake and stem over the heat gun nozzle, for a few minutes; it takes that long for the reading to stabilize.

When I graph this data, I get a straight line, where temperature error increases as temp increases. By my calculations, this means that:

To get a measured temperature of 400F after a few minutes of constant heating, it's necessary to set my Steinel heat gun to 460. That is without the stem feeding into anything, just shooting out into free air.

It took a few minutes for the temperature to stabilize, and the temperature was much less while warming up. For instance here's the temperatures measured every 10 seconds while warming up with the heat gun set to 500F:

0 sec 180 degrees ( I started with the apparatus somewhat warm to prevent the need to cool it down completely in between tests)
10 sec 230 degrees
20 sec 300
30 sec 327
40 sec 351
50 sec 370
60 sec 380
70 sec thermometer limit reached

When I preheated the heat gun and vriptech intake (the glass part that connects the heatgun to the stem) for several minutes first, it heated up faster:

0 sec 180
10 sec 237
20 sec 298
30 sec 343
40 sec 378
50 sec thermometer limit reached

But some of the slowness you're seeing is because the thermometer itself is slow to react. To find out how slow the thermometer is, I pulled it out, and then inserted it quickly into the preheated stem with the gun set to 500. I got the following results, which are very similar to the preheated numbers above. These numbers are basically how fast the probe reacts when immediately put into a preheated airstream.

0 sec 180
10 sec 270
20 sec 315
30 sec 340
40 sec 380
50 sec thermometer limit reached

So it looks like most of the warmup time I measured is from the thermometer itself taking its time to warm up. Therefore I cannot accurately say how long the apparatus itself takes to warm up, because I don't have an instant-reading thermometer.

I also did some experiments with blocking the airflow after the stem, to see if that would change the temperature. With the intake and stem on the heatgun, I would use some silly-putty type material to block the stem to varying degrees. Somewhat surprisingly, I found that blocking the airflow actually decreased the temperature measured at the location where the herb would go. The more blockage, the more the temperature drop, but it wasn't too much. If I blocked airflow almost completely that dropped the temperature 20-25 degrees after stabilization. Completely blocking the airflow dropped the temperature by 70 or more degrees, but that never happens in practice so who cares. When I blocked the airflow a medium amount, by putting the stem in my water pipe loaded with ice and a bag, the temperature only dropped 5-10 degrees. I suppose what happens is that when you block the airflow, less warm air reaches the location where the herb goes, because more warm air leaks out of the heatgun and intake seal.

So knowing this, here's how I look at the temperatures. To achieve a 400 degree bud temp at steady state with the stem shooting into free air, I would need a heat gun temp of 460. Because the water pipe/bag setup I use blocks some of the airflow, increase the heatgun setting to 470. Then you have to think about the fact that it takes a little while for the herb and apparatus to warm up, and in the beginning of your vape your herb will be at a lower temp. I usually preheat the heatgun and herb, but still I think it's likely that the herb is approx 10 degrees lower in temp for the first minute or so. So I increase the heatgun setting to 480. Someone who didn't preheat their heatgun or intake might want to use a higher setting like say 500.

So to get herb up to 400 degrees, I should set my heatgun at 480 and preheat as much as possible.

Before I did these measurements, I had been using 450-500 just because that seemed to give the best result, so it looks like these measurements are on target. Of course different heat guns may have different measurement issues.

FYI, the setup I'm using can be seen in the photos at:

http://420.marijuana.com/showthread.php?t=41307&page=2

By the way, this heat gun seems to hold the temperature very steady... once the temperature had stabilized it didn't change more than a few degrees. So it looks like the thermocouple and control circuitry are well designed in this heat gun.

 

5drive

Great info aze. Very helpful for heat gun users. I wouldn't aim for a vaping temp as high as 400 myself, since 365-370 will give you all the THC you're going to get while stopping short of toxin vaporization, but that's personal preference. The stable temp you observed shows why a forced air system is superior to a passive whip (lung powered) for efficiency.