On Fri, 28 Feb 2014 22:35:34 -0500, Stormin Mormon
wrote:

On 2/28/2014 9:16 PM, wrote:

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.

Heat can go into one of a couple places. Into the
house, into the cellar, up the chimney. When
efficiency drops SIGNIFIGANTLY, the heat is lost
some where.

So the burner shuts off, and the blower still runs.
How does this make the furnace less EFFICIENT? I
don't picture it. Shutting off the gas lowers
the efficiency? Really?

At church we have converted oil furnaces, which

Was it before or after you bought them that they converted to Mormonism?

now run NG. They have a high limit sensor in the
discharge air, when it gets to 110 or 120 it turns
off the flame. The three blowers keep running.

So, turning off the gas now and again makes the
efficiency of the furnace drop SIGNIFICANTLY?
How's that, again?

Almost in the same way. I think?, that driving short distances and never
letting a car's engine warm up to proper operating temperature. In
the case of the furnace, it may get that warm, but because it turns off
soon, a higher percentage of the On time is at the lower temperature.