I am planning on keeping my solar my 12 by 16 greenhouse between 35 and 40 at night all winter! There is no problems doing the day bt after about 9 pm the temp drops quick! I considered a small tankless 2.5 gallon hot water ank but aftering seing some things at tractor supply today I may have found something better! I don't need alot of heat since I have the bottom 2 foot perimeter insulated with 2 inch styrofoam and blue board all the way around! I have 250 gallon of water in 50 gallon drums plus some small containers! After dec is when the cold gets bad especially when it cloudy and cold for a week!
Tractor supply has a plug for $12 that turns on when the tem goes down and reaches 35 degrees. The plug is made to keep water for animals from freezing by turning on just about anything on a 110 circuit! I can put the plug in a location so it will go on and off as the temp climbs only 5 degrees!They also have 110 volt products that will heat water for the animals that could keep one of my 50 gallon drums at a nice 75 degrees while I have a fan blowing on the drum! keeping the top of the drum slightly open will give me the moisture I want! I may keep the drum nder my weat chamber for a two purpose use! This is exciting for me to see how it works!--- Any other suggestions that will generate a small amount of heat using electric?
I will also have a fan that kicks on and blows air againt the water barrels when the day temp reaches 50 deg or above! to raise the temp in the barrels quicker!