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Old 11-24-2014, 08:43 PM   #1
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Temp rise in furnace


I have a Ducane 95G2UHV90 2 stage furnace. The temp rise ratings are 30 - 60 (low fire) and 45 - 75 (high fire). I measures them and I am at the low end in both ranges. 30 degrees on low fire and 44 degrees on high fire. Is this acceptable, or should I back the blower off a bit to get the temps up? I clocked the meter on low fire and it is dead on with what is in the manual.

Is there an advantage / disadvantage to being on the low end of the team rise?

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Old 11-24-2014, 09:21 PM   #2
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Temp rise in furnace


You want to be in the middle. If it is too low it can condense water in the primary heat exchanger and damage it. Should have dip switch settings on the board as it is a V drive ECM motor.

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Old 11-24-2014, 09:41 PM   #3
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Thanks, Yuri. It has jumpers on the board to set the fan speed. Will move to the next speed down and see what the temp rise is. Thanks a bunch.
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Old 11-24-2014, 10:23 PM   #4
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Yur Welcome. Nice furnace.

Use a Merv 10 filter to keep the secondary coil etc nice and clean. Then check the temp rise.
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Old 11-24-2014, 11:32 PM   #5
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Quote:
I measures them and I am at the low end in both ranges. 30 degrees on low fire and 44 degrees on high fire. Is this acceptable, or should I back the blower off a bit to get the temps up?
The better 2-stage ecm furnaces (carrier/lennox/york/trane/goodman etc) come setup to maintain the same temp rise on high and low.

30 on low fire is too low and you should reduce the speed.
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Old 11-25-2014, 04:20 AM   #6
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Temp rise in furnace


Doesn't sound like your blower is running in its first sage heat speed. Do you have your fan set to run 24/7?
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Old 11-25-2014, 06:26 PM   #7
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Beenthere,
Have a Honeywell stat set on circulate so fan does not run 24/7. It does ramp up the fan when it goes to high fire, I just think the installer set the jumpers too high. I set it back to what the manual shows as the factory default and now I get 43 degrees rise on low fire. Did not feel like jacking the stat to get it to go into high fire. Not cold enough to get it to go into high fire except in the morning when it comes back from night time setback. And that's pre-coffee so any measurements taken then would be suspect.

Yuri,
Have the 3M 1900 pleated filter. Not sure what the Merv rating is on those. Change monthly.

User_12345a,
Lennox makes Ducane, but board might be different. Runs on low fire most of the time unless Yuri sends that Canadian air our way.

Thanks, guys.
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Old 11-25-2014, 06:54 PM   #8
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2-3 years ago they made Ducane/AirFlo/Armstrong furnaces identical to the Lennox as they bought Allied Air. Except for the high end mod SLP. Before that Ducane had it's own board etc.

There is some way to cross ref those 3M to Merv but you have to dig on the net for 1/2 an hour to find that site. Google works different than BING so try both.
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Old 11-25-2014, 07:32 PM   #9
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Low heat speed is nearly the same has high heat Ducane/AirFlo/Armstrong models.

I think it's to differentiate products and charge a premium for something with a lennox sticker on it.

Carrier puts crappy firmware on the ICP furnaces too; the variable speed models don't maintain airflow as the static pressure increases.
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Old 11-25-2014, 07:55 PM   #10
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Turns out they are Merv 12 filters
http://www.iallergy.com/filtrete-air...comparison.php

Furnace was 2 years old this September. Replaced an oversized York 80% unit. Really like the 2 stage heat and 2 stage cool. Saving a bunch on gas and electric and the house is more comfortable.

Last edited by chitownken; 11-25-2014 at 07:56 PM. Reason: fixed typo
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Old 11-25-2014, 08:09 PM   #11
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Temp rise in furnace


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Originally Posted by chitownken View Post
I have a Ducane 95G2UHV90 2 stage furnace. The temp rise ratings are 30 - 60 (low fire) and 45 - 75 (high fire). I measures them and I am at the low end in both ranges. 30 degrees on low fire and 44 degrees on high fire. Is this acceptable
Where are you measuring the temperature rise at. Measure the temp as soon as the heated air enters the plenum of the furnace. Do not take your heated air measurement at the register to calculate temp rise
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Old 11-25-2014, 08:46 PM   #12
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Measuring return temp about 2 inch before the filter where all the returns come together. Measuring supply temp about 1 1/2 inches above the A-coil in the supply plenum before any of the duct runs branch off. Temp probes go in about 4 inches or so and do not contact anything. Let it run for a few minutes to stabilize the temps.
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Old 11-25-2014, 10:18 PM   #13
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Temp rise in furnace


Quote:
Originally Posted by chitownken View Post
Measuring return temp about 2 inch before the filter where all the returns come together. Measuring supply temp about 1 1/2 inches above the A-coil in the supply plenum before any of the duct runs branch off. Temp probes go in about 4 inches or so and do not contact anything. Let it run for a few minutes to stabilize the temps.
I did almost the exact same as you last year to check mine. I used a "dual probe thermometer"

Note: in the first picture I have the leads incorrectly labeled as the probes.
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Old 11-26-2014, 04:27 AM   #14
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Temp rise in furnace


Quote:
Originally Posted by chitownken View Post
Measuring return temp about 2 inch before the filter where all the returns come together. Measuring supply temp about 1 1/2 inches above the A-coil in the supply plenum before any of the duct runs branch off. Temp probes go in about 4 inches or so and do not contact anything. Let it run for a few minutes to stabilize the temps.
Best to have your supply probe in the supply trunk, about 1 foot in. That way the sensor is not effected by radiant heat. And the air has a chance to completely mix.

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Last edited by beenthere; 11-26-2014 at 05:23 AM. Reason: Spelling
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