Closing some a/c and heater vents

[Bobbi]

I have climbed a ladder and closed a couple of the the ceilnig vents from which air conditioned air comes, in rooms that aren't being used right now.

I figured that this would free up more cold air for the remaining vents. I also planned to do this with the floor heater vents in the winter for the same reason.

Now a visiting friend told me he doesn't think this is a good idea, or not good for the a/c and heater.

Please advise!

Thanks so much.

[Tom]

Here is the rule of thumb that most HVAC guys follow:

Do not close off more than 20% of the registers in your house
This can cause high resistance and unnecessary heat build up in the furnace.
Tom

[Bobbi]

Thank you, Tom.

I find that the heating registers in the floor don't have a closed option, so I'll have to leave them all open anyway.

What about the air conditioning vents in the ceiling? I am able to close these. Does the 20% rule apply also?

[Tom]

No it does not. But at the same time you dont get the same sort of benefit by close off alot of cold air vents anyway. Leaving hot rooms is not always a money saver when using AC, one or two maybe but not much more than that. Tom