If you go away during the summer, I be inclined to turn off the furnace. During the winter, it would probably be better to leave it on low.
I have a friend using an oil fired room heater. He used to turn it off during the winter when he wasn’t in. Now he leaves it on all the time on its lowest output. He found that his fuel consumption decreased, compared with turning it on and off as he wanted.
I also have another friend in Norway who works away a lot. He once turned off his heating for 2 weeks one winter while he was away. When he came back his house was stone cold and it took ages to warm up the fabric of the house. he now leaves it minimum output when he’s away during winter periods.