I have a new furnace. Can I shut down registers in half the house to save costs?
Answers:
I wouldn't suggest closing the registers in more than 30% of the house, but generally it won't hurt the furnace in the short term. But completely closing off the heat to several rooms could cause problems with the paint in those rooms if they become too cold. Also I would suggest turning the water off at the main shutoff and opening a faucet to relieve the water pressure in your pipes, this way if something did freeze it is less likely to break a pipe. By closing off registers you are basically making the furnace too big for the space being heated. This isn't good for the furnace's heat exchanger and other parts and will eventually shorten it's life. It causes the furnace to short cycle, and it is this frequent starting and stopping that causes most service problems... much like city driving in a car verses highway driving. If you are doing it just this one time for a few months then there should be no problem. If you plan to do this on an yearly basis, then you will shorten the life of your furnace and also it will require more repairs during it's life.
Other answers:
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Yes, unless you use a heat pump. If you have a heat pump and shut down too many registers you will slow the air flow and can damage your compressor.
Closing registers will reduce the requirement for heat but not as much as lowering the thermostat a few degrees and wearing long sleeves. No problem leaving the furnace for a few months - make sure the heat - off - cool selector is on off or better yet leave it on heat with thermostat set at 60 degrees. This will insure nothing freezes up. If you have plumbing under a cabinet in an outside wall BE SURE to leave the cabinet door open when you leave to spend the winter in Florida. With the thermostat set at 60 pipes under cabinets could freeze if shut in away from the heat of the room.