Epoxy Heat Box: Fish tank heater?

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cattflight

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Maybe this belongs in Workshop/Tools but I wanted to narrow the focus to Composites. I see a lot of folks putting a light bulb in their insulated epoxy heat boxes. Hs anyone used an electric fish tank heater instead? With the built-in thermostat, seems it should work as well. Any issue with those heaters in the ambient air instead of water? Figured I could drill an appropriately-sized hole in the heat box and leave the adjustable head and AC cord exposed.

Thoughts?
 

Vigilant1

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I think the aquarium heaters need to be in water or they'll crack when turned on (they can't dissipate the heat they produce quickly enough without a water bath). They do make small rocks and pads for heating reptiles/reptile cages, but I don't believe they have thermostats.

I'd guess any heater with a built-in thermostat isn't going to keep the temp quite as well modulated as a remote thermostat.

Other thoughts:
A thermostat may not be needed if you use a light bulb, provided your shop temp doesn't vary much. The heat loss through the box sides will be fairly constant and you can just screw in the right size bulb to keep it where you want it.
The European 220V bulbs can be handy for this sort of thing. On US 110V circuits they will last virtually forever, and I think they use quite bit less wattage than you'd guess from reading their label (for 220V circuit). So, if you only needed a 20 watt (US, 110V bulb) to keep the box hot enough, you could get a 40 watt bulbs (220 V) and it might do the trick and never burn out.

I think Ohm's law applies here in some way . . .

Added: If you just want to keep the epoxy warm and aren't much concerned about keeping the glass cloth at higher temp, you could put the resin and hardener containers in a water bath and use the aquarium heater to keep the bath warm. Of course that will produce some high humidity, so don't store your glass in the same cabinet.
 
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Hot Wings

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I think the aquarium heaters need to be in water or they'll crack when turned on

Just put one in a jar of water, run the cord through a hole in the top and plug with silicone. Used one of these for years for my home built incubators.
 

Vigilant1

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I think the aquarium heaters need to be in water or they'll crack when turned on

Just put one in a jar of water, run the cord through a hole in the top and plug with silicone. Used one of these for years for my home built incubators.
But then the thermostat just functions to keep the jar of water at a constant temp, not the air around the epoxy. Right? If the shop gets colder the epoxy gets colder, but the jar of water stays at 78 deg. If constant heat output is good enough, wouldn't a light bulb be simpler?
 
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Hot Wings

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Actually the jar of water keeps the temperature more stable. The water will transfer the heat from the heater to the air with no problem. Most of the new aquarium heaters are sealed and preset at ~70F/22C. I buy older ones at garage sales so I can set them at 37C. I've never tried to open and reset one of the sealed ones, but it doesn't look like much of a problem.

One of the terrarium heaters with a thermostat would be a simpler option, but they cost 3X as much $'s
 

Richard Schubert

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For about $20 you can go to home depot, get a ceramic bulb holder, and a rheostst light dimmer an extension cord, and make a variable light/heat source. Mine works perfectly, I only have to change the setting twice a year when the seasons change. Radio Shack for the indoor/outdoor thermometer to monitor. Any thing above 80 degrees (F) and below about 120 is OK. I used a infrared bulb for 3 years until it burned out, replaced with a 150 W spotlight, works fine. Will hold the box at 85 with a shop temp of below freezing.
 

bmcj

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Actually the jar of water keeps the temperature more stable. The water will transfer the heat from the heater to the air with no problem. Most of the new aquarium heaters are sealed and preset at ~70F/22C.
But what about the effects of moisture on the epoxy?
 
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Vision_2012

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My take is to use a coffee cup heater. Will report this spring-summer's use.

edit: not enough power, switched to light bulb as heater, works fine.
 
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