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Main Boards => The Bowyer's Bench => Topic started by: Hoosierarcher88 on January 05, 2021, 06:29:43 PM
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Ok i have a few questions. We have a hotbox that we have built for curing wood of bugs. It needs to hold the wood interior temp of 130 degrees for a day to draw any bugs out of the wood. The box we have built is 8 foot long and about 12"x12". Its made of double thickness 1" foam insulation and lined with the foil reflective material. For heat elements we have 2 60 watt heat bulbs for reptile tanks. The issue is that both bulbs are on the same end which has no issue hitting 150° but the far end seems to top out around 108-110° ambient temperature. Does anyone have any ideas as to how to get the heat to circulate as most fans we have found have a thermal cutout at 120°.
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Buy a computer fan, cut a hole in one end of the box and mount it on the outside of the hole.
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I have a similar shape box but use two 4 ft T-12 flourescent shop fixtures with 2 40 watt bulbs in each one.
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I know everybody loves their light bulb heat, but it's inefficient. Ceramic infrared heat bulbs are actually made to heat things, better choice. Or better yet recycle a baseboard heater element for your heat source. Adjust the temp by moving the thermocouple and like Roy mentioned, use a small muffin fan for circulation. Computer fans run on 12v, so you might look into a 120v fan. AC Infinity makes a really nice axial fan that is rated to 250deg so you can use it inside your oven and not introduce outside air, uses 110v or 220v and costs less than $20. If you really want to get your oven dialed in, use a PID controller.
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The ceramic heat bulbs are what we are using rather than a regular light bulb. These are for things like reptile tanks. Im looking into the ac infinity fans now
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Those ceramic bulbs are pretty awesome. I'm surprised more bowyers don't use them instead of incandescent bulbs. Halogen puck lights work good also and are low profile. Before I switched to a baseboard element, I was using them. They must be a really inefficient light source because less than 100 watts worth would heat my box up to near 200deg, it just took too damn long to get there.
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Flem has a point about keeping the fan inside.
That would even out the temp inside the box.
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You also have to consider hot spots, places where the heat is more concentrated. Can you move one heat source to the other end of the box then add the small fan?
My heat box has 4 ceramic light sockets. Even though it has an inline thermostat(168deg max) I would control the heat by the number of bulbs I would light. Once I determined that, I would lay aluminum foil loosely over the bow under each lit light bulb to keep from overheating one area more than others. I also use a fan inside the box to distribute the heat more evenly. I also have a meat thermometer stuck the side of the box on each end to be sure the heat is even from one end to the other.
I also drilled 2, 1" holes, one at each end, one on top, the other on the bottom of the end panels. When drying staves I leave these holes open to allow the moisture to leave. For curing glue and for max heat retention I plug these holes with a cork.
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The rv supply stores sell a small battery powered fan that's used to maintain even temperature in a refrigerator. Not sure how it would hold up in the heat. Just thinking out loud.
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A computer or electronic repair shop will have small used fans that are made for dispersing heat.