A furnace could represent transformation, growth, or change. For example, if the furnace is heating up or being used in the dream, this could suggest that something in your life is undergoing a transformation or change. This could be a relationship, a situation, or even a part of yourself, such as your beliefs or behavior.
In some cases, the furnace in a dream could also represent your own inner strength or power. For example, if you are using the furnace to heat up a home or building in the dream, this could suggest that you are using your own personal power and strength to create warmth and comfort in your life.
If the furnace is broken or inactive in the dream, this could suggest that you are feeling weak or powerless in your waking life.