I am building a heat box to treat my all wood archery bows I build. I need the wood to get up to about 240 degrees so I can’t use steam. It is very important that I don’t scorch the wood so I am wondering if there is something I can install that will sense scorching. Possibly a smoke detector but not sure if it is sensitive enough. Aslo wondering if there is some rule of thumb I can use for figuring out the number and wattage of light bulbs I would need. Looking to bring box up to about 300 degrees and it would be about 6 cubic feet running horizantal . I am thinking maybe 6 100 watt bulbs should be plenty but not sure.
You can use steam. Steam can be at any temperature greater than 212 F.
How hot you’ll get with light bulbs depends on the shape of the box (mostly, its surface area) and what it’s made from.
The interior of the box wll be about 6 feet long and 1 ft square. It will have about 1 1/2" insulation and be made from sheet metal
Use ceramic heaters for terrarium use to get better efficiency, and use a thermostatic controller. I just built a system using this combination for a bearded dragon palace, got all parts very inexpensively from Amazon.
I don’t think reptile heaters will get hot enough for the OP’s needs. How about a heat lamp? They sell them at poultry supply places. You’ll probably only need one.
Pretty sure they will, but only just - which is why I thought they’d be better than something that gets way hotter and has to be cycled off frequently.
If it wasn’t so hot here, and thus the heating system for the cage not cycling on, I could use an IR thermometer to see how hot the 75W and 100W ones get…
ETA: I do mean the flat, black-brown heater “bulbs” for overhead use, not reptile-rocks or floor heaters.
Any sort of heat source will be nearly the same efficiency, nearly 100%. The power that you’re putting into the system will be almost exactly the power converted to heat. The only practical consideration I can think of is that you’d probably prefer multiple smaller sources over one larger source, to even out the temperature. And you’d have to make sure that your thermostat system (whatever it is) can handle temperatures that high, which one designed for a reptile enclosure probably won’t.
This is what I was thinking the more the better.
I’ve tried using those in a chick brooder and they don’t get the air hot enough for chicks, which require a temperature a lot lower than the OP’s needs. They are quite hot in the immediate vicinity-don’t touch one-but don’t seem to radiate the heat very well; maybe if you used a fan to circulate the air?
I can’t seem to find a temperature spec. I was thinking in a row on the bottom of the box, with the bow-wood on a metal shelf above them and the box sealed to keep the heat in. You maybe right that they don’t get hot enough, but I think they do…
I’d be inclined to use a silicone strip heater like this (you would need two of these).
They heat very evenly, and are easy to control.
I think a row across the bottom could work, I actually need more heat on the belly of the bow than I do the back so maybe drill some small vent holes in the top might give me a little benefit in directing the air flow.
Don’t know what kind of treatment you are doing but steam would do more than just heat the wood, it’s going to increase the water content greatly, the wood will swell, and if it’s not clamped or weighted down it’s going to bend. Unless you’re heating it for bending, and steam is used for that, you’ll want dry heat. I know people build small drying kilns using a heat gun, a thermostatic control, and just a flap for the exhaust vent. Not extremely efficient but to dry wood you need to rid of the moisture so it can’t be a closed system. Whatever heat source you use you want something to diffuse the heat to prevent scorching. Metal filter mesh would be good, for something like a heat gun with a fan. If you use strip heater you may just need a piece of metal over the strip.
I use dry heat for two purposes. I make gentle bends in the wood with dry heat and they seem to set better than if made with steam which is what I usually use for more severe bends. I als use the heat to heat treat the wood which makes it a little stronger in compression and less prone to taking set when bent.
The heat strip would work I think but not sure how much or what type I should be using. Eevn heat for about an hour and no scorching are my primary goals.
Well yes, but not at atmospheric pressure. Unless he wants to construct a pressure vessel capable of holding 10 psig, and given the size of the box he wants to build that’s not easy or safe for someone not up on the ASME boiler and pressure vessel codes, specifically Section VIII.
I think an electric heat gun like those used for thawing pipes and a thermostatically controlled switch would work best.
Ok, for one hour efficiency is not that big of an issue. With thermostatic control once it comes up to temperature it shouldn’t need that much additional heat. But keeping the heat even through the box is your biggest challenge without circulation. Strip heaters aren’t necessarily going to give you even heat along their length. Maybe you can put a fan blade inside the box on a shaft that runs through the wall to a motor on the outside.
First, it doesn’t matter what kind of bulbs you use: white, red, black; it all turns to heat in a sealed box. The only thing that affects the number of bulbs needed is how much escapes from the box, which depends on its size, shape, composition and, yes, its color since dark will radiate more heat. The most important thing is to get a thermostat set to the temperature required. You might also want a small fan to make sure the heat is evenly circulated.
I once built a small box to make yogurt in. It was wood, I put a 60W bulb in it and used a chick-hatching thermostat. Worked fine.
For long life and safety, don’t you use a portable cooking hotplate…
Put it at the bottom and convection circulates the air around to bring it all up to temperature…
You wouldn’t actually need a thermostat… you just need to calibrate the power level setting for the box…
Since heat loss is related to difference in temperature, the hotter it is, the more power it takes to keep it at that temperature… So once you bring it up to desired temperature quickly on full power, you can set the power control down to keep it there…