On Mon, 18 Feb 2008 21:33:56 -0500, mm wrote:

On Mon, 18 Feb 2008 21:05:47 -0500, Don Wiss wrote:

I believe you are correct. The heat uses the low speed and the AC the high
one.

Hmmm. That would mean that., if he has to change something in the
furnace (air handler?)** either he should make his change a little
more complicated, or he'll be using the high speed for heat as well as
AC. And I guess the designers don't think that is good. I'm not
assuming here that just because it's winter, his goal is to change the
heat and not the AC.

As heat rises you don't need as much fan to push it up into the house. Cold
air is heavy, and more fan is needed.

The ideal for AC is a variable speed fan and variable speed compressor. It
would adjust itself to be always running and keeping the temperature at the
set point. Then maximum humidity is removed. The top of the line Carriers
now have this. But to install this AC you also have to replace the whole
furnace to get the variable speed fan.

Many (most?) new furnaces these days run at 80% efficiency. That Carrier
can get up to 90%, but only if you install special air intake and outtake
ducts. It needs outside air to get the efficiency up.

Don www.donwiss.com (e-mail link at home page bottom).