Can anyone tell me if a furnace is factory set with the fan speed on high? I
have Armstrong(Lennox) Ultra80. Its installed a 2 story home around 3000 sq
feet. The manual does not state what the factory set speed would be and don't
want to mess around with the fan controller board unless I have to, not even
sure where its located.
Why are you asking?
It seems like an odd question. My guess is your question is more like
"What speed should my furnace be set to?"
Normally the answer to the question as you put it, will not be very
The manual wont tell you a thing. The INSTALLATION manual, that should have
been left on the unit, or near the unit by law (at least here) tells how to
set the fan speed based upon static pressure readings..you dont just go
mucking around with furnace fan speeds.
Most all modern units have a multi tap motor, meaning you have more than one
speed, normally they come with a 3 or 4 speed motor, and they have default
settings based upon what would be considered a proper duct system
They allow speedup, or slowdown, based upon the DUCT characteristics, and
heat rise, among other items...and not for on the whim adjustments.
Normally, in all cases, your AC will use a higher speed than the heat,
unless its a heat pump, and of course, yours is not.
Your thermostat will have the ON setting controlling a fan relay, and THAT
will be on the high setting as the same relay will be the one that is
activated when the AC is turned on. So, if you are using the unit to move
air, with the thermostat set to ON, and not AUTO, when the furnace fires, it
will continue, in most cases, to use the high speed setting. This can, have
a few disadvantages, such as reduced heat output since the heat exchanger
can not get to its proper temps, and increased wear on the heat exchanger
due to increased condensation IF the upper limits of the heat exchanger stay
cool. Also, the unit will never get to its rated 80% AFUE.
Couple of things come to mind...you have ONE unit, for 300SF...2 story
home....ugh. Its a cheap way to heat and cool a home, but the prefered
method in the case of 2 story homes is a set of units...one for the lower
floor and one for the upper..
Second thing is that with only one unit, (you didnt state size) you are
going to have some pretty big temp swings if the duct was not sized for this
Most are not.
Thanks for the reply, it was unlike most very informative. The reason I ask is
that the furnace fan just does not seem to blow very fast. The vents in the
bedrooms upstairs seem like the air flow is very light. In my old house the
furnace seemed to blow much harder. The furnace is a 125000 btu. The manual
does show how to set the fan speed at low or high by moving jumpers. I will try
the suggestion of setting the switch on the thermostat to on.
(The manual does show how to set the fan speed at low or high by moving
You might be wise to call a good tech. Don't make any mistakes when you change
The correct amount of airflow is critical to efficient operation of your
heating and cooling system.
The airflow needs to be properly balanced to all the rooms.
If you get the blower set on high speed, and have dampers in the ducts,
try adjusting them to balance the flow to each room as required.
Check the temperature rise. It would be wise to call a good heating &
air tech for a thorough evaluation of your entire system.
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