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#4548472 - 10/19/17 04:22 PM new furnace multi speed blower.
JustinH Offline

Registered: 04/17/04
Posts: 5174
Loc: Texas
I purchased an American Standard AC and Gas Furnace for my home.

We ran the furnace for the first time a few mornings ago to take the chill off the house.

When on heat mode the furnace blows at a very low speed for the first 20 or so minutes, then it increases the speed after 20 minutes to what I could consider normal.

It is a standard 80 percent gas furnace from their Silver line.

I was thinking about why it operates like this, when our old furnace would just blow on high and warm the house up almost instantly then shut off.

I also noticed in "Texas winter" we would get some condensation on the inside of the windows during cold snaps.

So am I correct to think that the furnace has a variable speed blower on the heat mode, and it runs a long time at a low speed to drop the room humidity, and if the temperature is not satisfied after X amount of time, it ramps up the speed of the blower?

We live in a climate where it is not uncommon to run the heat in the morning, and the AC in the afternoon.
'11 Hyundai Sonata GLS
'11 Scion XB

#4548500 - 10/19/17 04:59 PM Re: new furnace multi speed blower. [Re: JustinH]
benjamming Offline

Registered: 01/03/04
Posts: 5919
Loc: northern Alabama
I also have a variable speed furnace. It does that using an ECM motor which is pretty neat as explained on York Central Tech Talk.

But if you need to troubleshoot it, then here's a site that might help. ECM Motor Troubleshooting
And perhaps a handy tool at the Dealer Toolbox.

#4548502 - 10/19/17 05:04 PM Re: new furnace multi speed blower. [Re: JustinH]
Fitter30 Online   content

Registered: 05/05/13
Posts: 99
Loc: Peace valley, Missouri
what's the model number of the furnace?

#4548511 - 10/19/17 05:16 PM Re: new furnace multi speed blower. [Re: JustinH]
StevieC Offline

Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
Mine has dip switches that can enable / disable this feature and just uses 100% duty cycle with full blower all the time when there is a call for heat from the Thermostat.

You can also change the speed of the circulation fan if you want to keep it running all the time. I changed mine from slow to medium by moving one of the wires inside.

The ECM motors are nice because they use minimal power, last virtually forever and if you want to keep the air always clean and the temperature balanced throughout your home you can run it 24 hours a day by setting the fan to ON from AUTO.

Edited by StevieC (10/19/17 05:19 PM)
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#4548512 - 10/19/17 05:17 PM Re: new furnace multi speed blower. [Re: JustinH]
Donald Offline

Registered: 03/21/04
Posts: 20455
Loc: Upstate NY
Is it a modulating gas furnace. The flame will got to full if it does not reach temp in 15 minutes. (Or something like this scenario).
2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
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#4548513 - 10/19/17 05:17 PM Re: new furnace multi speed blower. [Re: JustinH]
ZZman Offline

Registered: 03/17/08
Posts: 5780
Loc: Michigan
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#4548543 - 10/19/17 05:48 PM Re: new furnace multi speed blower. [Re: JustinH]
sleddriver Offline

Registered: 02/06/10
Posts: 4602
Loc: Central Texas
Originally Posted By: JustinH
I also noticed in "Texas winter" we would get some condensation on the inside of the windows during cold snaps.
Do you monitor indoor humidity levels?
1998 Volvo V70 T5 226,808 mi. Original Owner.
M1 10W-30 HM
"It's never a mistake to buy tools, defined broadly. They're not a cost, they're an investment." - J.B. Peterson

#4548584 - 10/19/17 06:46 PM Re: new furnace multi speed blower. [Re: JustinH]
JustinH Offline

Registered: 04/17/04
Posts: 5174
Loc: Texas
yes my wife bought me a weather station. It works pretty well about 39 percent humidity indoors today. Usually around 40 during summer.
'11 Hyundai Sonata GLS
'11 Scion XB

#4548986 - 10/20/17 08:15 AM Re: new furnace multi speed blower. [Re: JustinH]
greenjp Offline

Registered: 05/19/04
Posts: 1306
Loc: Germantown, MD
It sounds like you have a variable speed, 2 stage furnace. I have the Trane equivalent (XV80) of your American Standard (they're the same company).

The low speed/1st stage isn't for humidity control (just heating the air doesn't affect the moisture content - any drop in humidity associated with the furnace is from outside air being pulled in), but rather for general comfort. Longer run times provide for more even heat throughout the home, and the quieter operation of the furnace and airflow are nice.

The way it should be set up is with a 2 stage capable thermostat. The thermostat will look at the set point and measured air temperature and decide if it should be running in the 1st or 2nd. It will not just switch over to the 2nd stage after some predetermined amount of time. Mine (a Honeywell) will only turn on the 2nd stage if there's a large delta between the set and measured, or if it senses that the 1st stage isn't able to maintain the set point. It runs on the 1st stage most of the time.

Now, if you have only a single stage thermostat, or if they've configured the furnace incorrectly, it'll run in that basic 1st stage for a while then switch to 2nd stage whether it needs to or not. My Trane would do this after 10 minutes.


#4549875 - 10/21/17 06:46 AM Re: new furnace multi speed blower. [Re: JustinH]
JustinH Offline

Registered: 04/17/04
Posts: 5174
Loc: Texas
Thanks, so I have a multi stage Emerson Sensi thermostat.

However it was setup for single stage heat and single stage cooling.

I have single stage cooling and 2 stage heat.

I will have to look if I have the secondary wire for multi stage heat, if not I will need to run a new thermostat wire harness (not too bad of a job, I run network cables at work all the time).

For now the furnace heats on "dumb" two stage mode, I think 10 minutes or whatever at low stage then high stage.

I may not even mess with it, because we don't use the furnace too much anyways.
'11 Hyundai Sonata GLS
'11 Scion XB

#4551060 - 10/22/17 01:55 PM Re: new furnace multi speed blower. [Re: JustinH]
JustinH Offline

Registered: 04/17/04
Posts: 5174
Loc: Texas
Ok so I was wrong about what I have.

I have an american standard AUE1A040A9241AF furnace.

From what I have read online, it is a single stage AC and single stage furnace.

The blower can be adjusted manually for 4 different speeds.

I will probably just leave it alone.

The manual describes 4 speed settings I can move wiring around to change the speed.

I'm kind of glad I don't have to run a new thermostat 5 wire setup, as the run looks a little more challenging than what I usually do..
'11 Hyundai Sonata GLS
'11 Scion XB