Unused rooms....Should I close the vents or leave them open


Old 05-15-14, 03:49 AM
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Unused rooms....Should I close the vents or leave them open

I have a two story house. I do not use the upstairs at all. There are 4 rooms up there.. Should i close the room vents? Close the vents and doors?? Close the doors and open the vents?? Should I open the vents. Open them just a little bit???............ If I ask 10 HVAC guys, 5 will say open / 5 will say close???. Any thoughts out there??
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Old 05-15-14, 11:10 PM
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I don't think any competent HVAC tech will tell you to close the registers in four rooms unless your house has twenty or more rooms total. The furnace needs to have a minimum airflow through it to keep the heat exchanger from overheating or the cooling coil from freezing. Closing off too many registers WILL upset the airflow significantly UNLESS you have a "dump" zone in the house that opens a damper when the airflow drops too low. This problem may be somewhat alleviated if you have an ECM (variable speed) motor which will have a tendency to increase the speed to overcome the added resistance in the discharge ducts.
Old 05-16-14, 04:48 AM
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Should have dampers installed at the branch-take-offs which you could adjust during the heating season so the temp-rise does not go above the furnace rating usually 60 or 70F temp-rise MAX.

Do not block-off Return areas as that can buildup excessive pressure in a room that is forced outside.

A lot depends on the duct & diffuser sized capacity going to the first floor area; of course the heating & cooling will no-doubt be considerably oversized for only one floor area.

If the cooling coil is going to be under-loaded installing a TXV refrigerant metering device plus a suction line accumulator will help prevent liquid refrigerant from slugging the compressor...

Last edited by HVAC RETIRED; 05-16-14 at 04:52 AM. Reason: adding needed info
Old 05-16-14, 05:11 AM
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Where's the thermostat located? If it's on the 2nd floor, you've got to leave the system as is.
If it's on the first floor, you may be able to throttle back the 2nd floor registers a bit. Don't close them, just reduce the air flow maybe 50%? Then you'll have to monitor the system for a few days. Things to look or feel for would be an increase in humidity downstairs do to short cycling or as others have said, a possible freeze up. If the system performs ok, you should notice the temp increase on the 2nd floor while maintaining a comfortable level on the 1st.

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