Hot box.

[doc henderson]

I have a hospital fluid and blanket warmer I use for drying finishes faster.  I have done some small scale heat treating as it goes to 160°.  I hate to abuse/ruin this unit as it allows me to do three coats of spray poly a day, and finish gifts and projects faster like coaster.  I can also sterilize and kill bugs, but the humidity from the wet stuff, condenses on the glass and runs down, so long term it would degrade my warmer.  I have been wanting a heat treat box.   I want to put in 8 foot stuff.  bigger will take longer to heat up so maybe 2 x 2 feet dimension, or 2 x 4 feet tall.  You have seen how I sticker single logs and that is what I have in mind.  I did get a replacement 5400 watt dryer heat element for 26 bucks.  I will need a fan.  I could use halogen work lights as well.  the dryer comes with thermostats and thermal fuses for control and safety. I recall the isocyanate insulation tolerates heat better than the pink or blue board stuff.  



 

element from Amazon.



 

 

 

wood to sterilize and dry a bit.  wet pine went from over 32 to 10% overnight.  lots of worm holes.  not good for gifts.  
this is talked about in other threads, but, lets dedicate this one so I can get al the best ideas and include in this build.  I can run it off the 30 amp 220 service that several of my bigger tools run from.  or may locate it outside instead of the shop.  in case of fire.

[doc henderson]

would not mind a variable heat control.  and need a monitor that goes higher than the home stuff.  What say you all.  or yall.

[tule peak timber]

Super! Also take a look at rockwool for insulation. ;D

[Larry]

and need a monitor that goes higher than the home stuff.  

This
Kiln heat controller in Drying and Processing

It has worked well since I installed it.

I have a friend that has a hotbox and he built a controller using parts from adafruit.com.  The controller connects to his home wifi through adafruit and he can control the temperature from his phone.  It also gives him a graph to show the history.  The parts were cheap but the knowledge to put it together is way beyond me. Adafruit does have a learning center but I think, at least for me, it will be better if I get my friend to build something for me. :D

[doc henderson]

so I reached out to Kyle, my high end heat and air guy, and he says he can build a galvanized box, insulated with "duct liner" good to 195.  He is going to look for a thermostat for variability.  He of course thought we should tap into my NG boiler in the basement, but I want it sorta portable.  the 5400 watt, dryer unit is only 22.7 amps and can run on several of the 220 plugs in the shop,

[Wlmedley]

That insulation I put around my stove pipe should be good for a pretty high temperature but I don't know where you could get wider pieces of it.

[doc henderson]

I think I have one of the bird ones, I got in the past prob. based on the thread recommendation.  

[Baxda]

I used an old clothes dryer to build something similar to this Dryer heater
It has a simple t-stat like used for an oven that has a temp range of 90-230f. I connect it to my hot box with metal duct and the temp probe is in the return coming back to the heater. 

[doc henderson]

I have tested it out on the bench.  all of the safety thermostats and fuses are rated for 110.  I guess with alternating current, the function will stop if you break the circuit on either leg of the 220.  (2 legs of 110V).  AC kind of moves back and forth and 110 needs a common to complete the circuit.  the ground goes to the same bar as the common in the box. on 220 the ground bonds the metal components of the heater, with ground so if there is a short, it trips the breaker.

nice video.  I hope I do not build one of those but I guess it did give me some ideas on the box and ducting.

[Walnut Beast]

I used an old clothes dryer to build something similar to this Dryer heater
It has a simple t-stat like used for an oven that has a temp range of 90-230f. I connect it to my hot box with metal duct and the temp probe is in the return coming back to the heater.

Pretty amazing what can be done on the cheap side if you take the time and save some 💰

[Baxda]

If you use the dryer element and appropriate fan heat up time should not be an issue. My box is 12'x30"x16" or about 40 cubic ft, and it only takes a couple hrs  to bring up to 160*f with it full of 1x6x10. Then I let it run overnight.

[doc henderson]

what do you use to heat yours?

[Baxda]

I use my version of the clothes dryer heater in the video above. I built mine with the intent to connect it with 4" metal duct and be thermostat controlled. It has an element similar to the one in your picture in the first post. 
Here is a picture before I put the front cover on

 

[Sod saw]

.


Doc, You are correct in that when you break the circuit of either hot leg of 220 volts, the item (load) will not function.  

However, , ,  Just because you have broken that path on that one leg from that 220 volt source, you can still get an electric shock due to the electricity flowing thru the item (load) from the other still connected (hot) leg as it is still connected to 1/2 of the 220 volt circuit.

Therefore: the best course of action is to have all fuses or circuit breakers or switches actually turn off both hot legs together so you are confident that when the item (load) is not functioning  there is no live "juice" to get zapped with.


.

[doc henderson]

I had thought of a 110 V relay with 220V contactor.  It will have a ground to metal parts.  thanks!

[JoshNZ]

My kiln unit has 2 elements they're exactly what you'd see on top of an old stove range I think, with a pair of fans blowing through them. They draw about 11-12A at 240v the pair. That is used to heat a whole 20ft container I would think just one of them would be an easy overkill for a 2x4x8' box.

~2800watt for the 20fter so if you found one that you could run on a normal 10A circuit you'd still be getting 1200watt. A little under half the power to heat ~5% of the volume.

I setup a raspberry pi board to run my kiln and it hosts a web page I can check from my phone, would be perfect to implement the same thing here but would take a bit of ground work getting up to speed on the pi and software if you're not already. Is it something you'd really need or would a tstat with a dial and a reminder set on your phone be better