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Maybe a clear enclosure in the sun of a window to heat up in the day. The water in the jars will act as a heat sink. You could add some bricks in there for more thermal mass to hold the heat longer, and maybe add warmed bricks as needed at night. Could cover it with an insulating blanket at night to keep the heat in. Just thinking out loud... Making sure the enclosure doesn't get to hot inside will be important. Posed a private question regarding shop setup earlier on discord. Cheers.