[Wes Tausend]

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jams

I think it theoretically would help to close off some rooms, but help only by the meager insulating value of the interior walls.

As an example, if the furnace was heating less cubic feet of air, and it would be, then it would not run as long. But since the wall surfaces to the cold rooms would be extra cool, the furnace would kick back on sooner.

Some of the posts mentioning efficiency could also be relevant. Typically, since the furnace ductwork would be restricted, less air velocity would move past the heat exchanger. In gas fired units, this would result in slightly more "un-exchanged" heat remaining in the exhaust gases going out the flue. This loss would be prevented only if you could plumb more ductwork into the heated rooms so that velocity was maintained. Electric element heaters wouldn't be affected and I think heat exchangers would somewhat recycle the heat energy, perhaps not as efficiently, or at least any heat loss wouldn't go out the flue.

Some changes in high efficiency gas furnaces actually have been higher fan (ductwork) velocity, but it is less comfortable in that absolute air temperature drops slightly and the now noisier registers deliver the feeling of a cool breeze in the room. But from an efficiency standpoint, the hot flue gases are "transfered" so cool they can be vented with plastic pipe. They are so cool that the old-time hot chimney effect (convection current) does not self-vent the chimney and burner fans must blow the combustion products out the vent.

We are very heater minded up here in ND.
God, this is a long winter.

Wes


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