Overpowered DIY heat treat kiln?

T

TrevorT1

Joined
Jul 2, 2025
Messages
5
Hello everyone,
I’ve been going down the DIY kiln rabbit hole as I’m sure many of you have done before me and arrived at a design I’m cautiously optimistic about but just as I proudly wrote out the final summary page I got a nagging feeling in the pit of my stomach. Is that too much power/volume?

Of course drew a lot of inspiration from YouTube, forums and gleefully going through the Kanthal design calculations. But compared to even heat/paragon kilns the DIYers seem to go for broke with their power density and I’m wondering if any longtime DIY kiln owners have any regrets about getting power hungry?

Initially based my design on someone who said 1W/cm2 of internal area was a good target but looking at current models on the market I have 15% more power/volume than the most dense model I found the paragon KM14T

For reference my design:
Interior dimensions: 6” W x 4.5” T x 17” D
Volume: 0.266 ft3

2.5” k23 firebricks

Power: 2500W (240V 10.4A)

15 AWG Kanthal A1 meets their design requirements with 3 runs along the sidewalls in series

Power/Volume: approx 9400 W/ft3

Appreciate any feedback
 
That's a small space and my concern would be getting longer pieces out with the low height but maybe that's just me....many do that with a propane forge. I like to put my blades in spine down and not laying flat and use a stand to accomplish it. That takes a bit of height.

The only real problem with "over powering" a unit would be that you could heat it beyond the capacity of the weakest link in the design. For example, failure of a switch that leaves it "stuck on" could get way hot and way fast. You need to make sure the controller is reliable and can be scaled for heating rates....if it's all the way on or off, your electric bill may surprise you and it may overshoot your programmed temps by a fair amount in such a space.

I'll say that sounds high power compared to the inputs on my Evenheat which is quite a bit larger, but what are your biggest concerns and what temp will be your top end?
 
The height is a good note. Current planning to be able to accommodate a 10” chef knife max. Just playing around so not looking to sell anything just have some fun.

Will be using an on/off PID controller with relays in the same configuration as most DIYers haven’t settled on a model yet.

I want to be able to work with stainless so will be in the 1950F ball park as an upper limit. Know I’m over reaching right now but want the option.

Biggest concern is the brick/mortar being shocked by the temperature ramping up to quickly and getting damaged. Not sure if that’s a valid concern or not.
 
if you use foil, add another 1/2" to the blade height and another 3/4" if you use a blade stand to hold the blades upright. I may add in some Kindle pins to my bottom layer of brick and my next build instead of using the stands I don't need as much height inside. I went with coil over tube construction along the top, so I lose some height already.

You can also program the PID to do a slower ramp if you use a ramp soak capable pid or change the temp periodically manually?
 
Thanks Taz. Saw JT’s build and just read through yours. I think you have the right idea so long as I get a programmable PID with a ramp function like the Auber which I was leaning towards anyway can put my mind at ease by moderating at least the first 1200 or 1400F when the temp can change a lot faster.

On a side note would love to do the coil over rod design too but would need to start from scratch on the design. Did you end up switching out to K23 bricks and getting better ramp up times, any issues?
 
I actually picked up 40, 3" K23 locally last week and the glass tubing arrived this week to start my rebuild! Slated for later in July when I am on vacation again!

Get the Wifi PID or a Bluetooth one, even with a non ramp PID. Sooo much easier to program over the phone than to use the control pad on the PID itself.
 
Nice! Also found a comment from Redbeard Ops on his YouTube video that his build is still going strong after 4 years with the same coil. Similar Power/volume not sure how much heavy use it gets but mine will just be for hobby use, friends/family showing off my gorgeous mostly functional chef knife to tinder dates. You know standard stuff
 
I HIGHLY recommend reading up on how to properly select the wire gauge as if you do it wrong your element life will be very short. The last oven I built I cheated the system and twisted 2 wires together and then coiled it. This gave me the gauge and resistance I needed and it’s holding up amazing. If you need any help let me know.

Also consider proportional pid controllers. These are basically like a PWM light dimmer. This gives you an actual percentage of power control from 0-100%. A normal pid controllers cycles from off to on and try and keep the temp stable by cycling fast. At high wattage this can wreak havoc on shop lighting and lighting in you house with flickering.

This set up will also give you much better element life as it will settle into a percentage of power to just hold the temp. This greatly improves temp stability and practically removes overshooting. On long ovens I would consider installing 3 thermocouples and with the right controller you can look at all 3 inputs. Or put a hole close to the door, middle and at the rear. Then you can probe the holes and see how consistent and even your interior is. You might be surprised how much cooler it is right at the door.

If I did another long oven I would break the elements up into 3 separate circuits and control them individually. But that’s for say a 30”+ oven.
 
Hi JT,
I haven’t considered a proportional PID. Any particular model you suggest? Don’t want to go crazy on price. With the auber wifi model Taz suggested would be in the $150 ball park who’s features are enticing enough to forgo that sweet little $50 inkbird.

Ran through the Kanthal design calculations on their website and should be in spec with 15AWG. For coil in groove on/off control at 2100F (above my intended use) max surface load is 2.24W/cm2 I ended up at 2.15W/cm2. Coil outside diameter is a hair over and stretch is 2.31 in the 2-3d tolerance.

Apart from the 3mm minimum diameter and and 150mm maximum loop length which I haven’t seen anyone achieve should be ok for the element design. I hope… probably.

As for thermocouples was just planning on one in the back. With a relatively small volume and only 17” deep hope with the tang towards the door will have sufficiently even heat on the blade

Do intend to use some high temp cord to help seal the door best I could find had an 1800F upper limit but seen others use lesser temp cord so will have to see how it works out.
 
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