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It sounds like poor insulation for one thing but here are some considerations. In the day time you have less load on the unit usually due to sunlight and outside temps being warmer. With what you are describing the thermostat may not work as well at 63 and to be honest you save no money going that low. The furnace will have to compensate the next morning to get the temps back up meaning an extended run time. Try 68 and see what happens. That may increase the cycle times. You didn't say what type of furnace or if it's central heat and air etc. If it is a heat pump by all means keep it about 70 at night to let it run longer and cut on and off less frequent.

Here's some advice for people with Central heat and air. Do not close off registers in unused rooms or completely shut off any room. There should be about a 2 inch gap at the bottom of the door for air return on closed doors.

You can damage your unit and shorten it's life doing so especially on the cooling cycle or either cycle on a heat pump. It needs the return circulated air to function properly.

Thanks so much for answering!

It is central heat and air-conditioning in this house. The landlord has no desire to add more insulation, and you're right...it needs more.

The furnace does have to compensate in the morning--first thing I do when I get up is turn the thermostat back up to 71 or so. I've wondered with all that extended run time in the morning if I was just losing whatever savings I had gained during the night.

I think I'll take your advice and try leaving it at 68 during the night.

From your comments....were you saying that it is better for heat pumps to run longer, but not central heat units?

The man who installed the digital thermostat set it to have a longer run or cycle time (or whatever the term should be) instead of the short one--he specifically said that. Guess he knew what he was doing. The furnace seems to run an awfully long time when it's on, no matter what the thermostat is set on-- the lower or higher degrees alike.

I really appreciate your comments and hope you don't mind answering another question for me. :)