http://beesource.com/resources/usda/electric-heating-of-honey-bee-hives/
Beesource has told about hive heating but this whole story does not make any sense with its bundles of wires.
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Yesterday I put a terrarium cable into a nuc, 4 frames. I know that 3W is enough to such colony. I put only 1/4 cable inside the hive.
Cables produce heat W/metre.
Then next day or after a week you may look, (and it is better to do), how the heater works. Idea is that the cluster is calm and together and bees do not walk around the hive. = they must be in rest mode.
There are difference, if you put the heater onto floor, between frames or over the top bars.
In hard frost days the bees collect them selves arround the heater and in mild days the cluster has spread wide in the hive.
You can see this all with your own eyes. Then use your brains and do not run to internet.
When I started my heating experiments, I bought all kind of heaters, what I found from nearest pet shop. 3W, 7W, 11 W, 15 W, 20W.
Well, next day I knew which worked .
40 years before that on old fart 75 y old beekeepers has showed to me how he uses light lamp as heat source above the inner cover. So he heated the cover board.
So it took 40 years before I tried how heating works. We visited often with my boy in pet shops and there I saw water resistant terrarium heaters.
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Such story.
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