Energy saving questions

So what's the general conscensus on closing vents and shutting doors in unused rooms in your house to save energy? I did this for a long time and then when I got a new air conditioner installed, the installers told me it's harder on the unit and you get better efficiency if you have complete flow through all the vents etc. Then I was just on moneycentral.msn.com and they were saying close vents to unused rooms and shut doors. What gives?
Also, what amount of degrees should you have your programmable thermostat go up or down (depending on season) while you're at work? I know if you make too drastic of changes you end up spending more on the drastic changes.
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Your system needs a certain amount of airflow to run properly and not damage your furnace. No one can say if your system ductwork is designed for it. Someone must calculate airflow for you. Sure you save , but do it right. Set backs are good , But only set back what it cools down in a hour or 2 or all you do is just reheat at the same cost.
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This makes no sense to me. Could you explain why it would take more heat to re-heat the room than you save by having it cooler.
Bob
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If you turn it off. you just reheat. What do you save? If you lower it to where it will be after a few hours and leave it for say 8 hrs . you spend less btu to maintain it at that point. For each degree heated you spend a certain %
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If you turn it down 6 degrees , but it doesnt reach 6 down till you turn it on again all you do is reheat all lost heat. Maybe you save a little, Its a debateable situation. Heating lived in rooms more, and keeping overall temp lower, Insulation, and more efficent boiler are sure ways to save.
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