On Fri, 28 Feb 2014 21:16:31 -0500, wrote:

On Fri, 28 Feb 2014 21:13:19 +0000 (UTC), DerbyDad03
wrote:

If you close off your combustion air vents, you risk carbon monoxide
poisoning.

http://www.centralheating.org.uk/Cen...iler_Flues.htm

You need to catch up with the rest of the world.

Just so that there is no misunderstanding, my cold air returns are not my
"combustion air vents".

While I do draw combustion air from inside the house, it is drawn in right
at the furnace through a dedicated inlet pipe.

Closing a cold air return in an unheated room won't impact the combustion
air intake.
No, but it MAY cause the furnace to "short cycle" because the plenum
temperature will rize too high due to restricted air flow. This causes
the high limit switch to shut off the burner untill the blower sucks
the heat out of the heat exchanger, when it will relight. This makes
the efficiency of the furnace drop SIGNIFICANTLY.

Hmmm. That's a serious concern. Thank you. How short do you think
too short an ON portion of the cycle would be?

Also there should be some way to know if the furnace is turning off
because the thermostat reached the desired temp, OR becaues the high
limit switch turned it off. I realize now that I don't know why my
furnace turns off.