kevins_news wrote:

My house (and furnace) is now 1.5 years old. Brand new construction
1.5 years ago. Since it is our first house we didn't think about
things like putting in a different furnace. We picked the colors,
cabinets, hardwood, countertops, and just let the builder put in all
their default models for things like doors, windows, furnace, etc.

I assume i have what people call a Natural Gas Mid Efficiency furnace.
Since all the high efficiency ones advertize multiple fan speeds
(which mine doesn't have) i would assume mine isn't one of those.

First some questions:

Are the energy savings from HE furnaces in the electircy needed to run
the fan? Or the efficiency of burning the gas (ie uses less gas to
make same amount of heat)? Or something else? And what is the
purpose of multiple fan speeds? Is this so you can leave the fan on a
low setting constantly to keep air circulation happening? Other than
allowing the air filter to be constantly working, what is the purpose
of this?

Would it be worthwhile to replace mine with high efficiency even
though it (and the building) is so new. two story, 1700 square feet
townhouse. On the main floor only two walls are exposed to the
outside. The other two walls are shared with neighbouring townhouses.
Our entire 2nd story is exposed though since neither neighbour has a
2nd floor.

We are pretty energy conscious so i bet the furnace is already
running less than the average household. I'd hate to spend $3000
(Canadian) on a furnace and find out i save only $100 a year in
gas/electiricty.

Are there any theoretical numbers? A TV commercial says "It will save
the average household X dollars a month" but with no indication of
what "average" is. Maybe someone has a study where a mid efficiency
furnace runs for X hours a day to heat the house, and a HE furnace
would only run for Y hours. I could use that ratio to estimate
something.

Any thoughs appreciated.

Sure, calculate the annual therms and cost of your gas now.
Find out the efficiency of your current furnace and the
efficiency of what you would replace it. As a ratio of the
efficiency ratings, calculate the annual therms. You will
probably find that your payout on a $3000 furnace would take
forever. If you like your present furnace, forget it. The
more efficient furnace will likely be more noisy.