Minimum wattage for aquarium heater

[Nolly]

I'm trying to get an early start on winter prep, especially since I have to buy everything I need. I wanted to known if anyone had experience to lead me to what might be the lowest wattage heater required to keep the water from freezing.
I plan on using a 2 gallon stainless pot with lid with horizontal poultry nipples installed. I live in SE PA (zone 6b).
I can get a 25 watt heater, but I don't know if it will have to run continuously just to keep the 61 degrees F that is its minimum. I'd prefer to use less energy than more. I intended to have an LED light of some sort on a timer for the chickens during the short days. This won't add much to the overall heat of the coop.

I am still open to other suggestions and solutions. Since I already have the stock pot setup made, I'd like to try to stick with it.
Ultimately, I think something that would just keep the water at about 40 degrees would be better, but the only thing near that is a pond heater and I don't think it would work well inside a relatively small pot.

 

[san415]

Just incase you have problems ( I did) I have just used two dog bowls that are heated. The work 100% of the time, even if 3 feet of snow covers them. I just shovel a path to them and remove the snow thats on them.
I have tried several other waters that are heated and meant for chickens, but 2 were so hard to fill and one failed. The heated bowls for dogs are easy to find and are cheaper.
I have a jug (from unscented cat litter) with a lid, that I use to refill the dog bowls as I leave for work. Then I just bring it back in the house when I get home and fill it for the next time.
I live in Michigan.

 

[pdirt]

First off I'll say I am no longer a fan of those submersible aquarium heaters. The one I had didn't shut off like it is supposed to when I accidentally let the water run dry. My bad, yes, but it could have been much worse.

Also, I am using less electricity with a 250w stock tank deicer. It turns on at 32f and off at 42f. The lowest most aquarium heaters will go is 65f. Don't let the 250w fool you... Because of the higher wattage, it takes less time to bring the water up to temp, then shuts off. A 25w heater will be running electricity more of the time, because it will take longer to bring the water to temp because the heater isn't as powerful.

The K&H stock tank deicer is designed for outdoor farm use. It shuts off in the absence of water, like it is supposed to (unlike the aquarium one I had). When water is present again, it turns back on. I paid $35 for it, which was $3 more than I paid for the aquarium heater. Also, a higher wattage heater will last longer than a lower wattage one, because it isn't operating as often.

I know the aquarium heaters are popular here on BYC, but I don't think they are safe.