Below 30* is an average. How long depends on the type of heater. Obviously an electric block heater will take much longer than an AquaHot. I'd leave the electric block heater on overnight if leaving in the early AM with sub freezing temps. Aquahot with an already warm boiler will only take a few minutes.
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1976 Newell Classic (Sold)
Home Base: Riverside, CA
If anyone needs my contact info private message me and I will send it to you.
-Joseph-
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