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CFM for heating

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Pops1

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Discussion starter · #1 ·
Just had a new Goodman GMES96 80k 17" installed and I'm looking at the heating settings. From what I see, even though there are 4 basic speed options in the manual, there's only one choice for this unit based on the rise. Using .5 on the chart it says:

CFM. Rise
453 N/A
1009 "65"
782 N/A
951 N/A

So does this mean that they're not adjustable; there's really just the one setting (at 1009)? I assume N/A is not advised or does it mean you can't even set it that way?

I think it's even more confusing if I had a 60k unit as the "one setting" they show is at a rise of 50 whereas my 80k unit is already at the top of the rise range...heck, I'm surprised they would offer the unit to push the full 1200CFM to keep that rise a little lower but I get that they don't want a windy house in winter.

Thanks
 
#2 ·
This is all supposed to be set by the installer after testing several operational parameters. It is not meant for the homeowner to experiment with.
 
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#3 ·
If your duct work is adequate or better often the speed can be lowered, if it is normal then even the highest speed is to slow. As Doc said all this should be set up and tested by the installer, and better yet it would be analyzed before the installation to know if the duct can handle the needed air or if other equipment is needed that will work with the duct or if adjustments need to be made to the duct.
 
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#4 ·
Pops1 said:
Just had a new Goodman GMES96 80k 17" installed and I'm looking at the heating settings. From what I see, even though there are 4 basic speed options in the manual, there's only one choice for this unit based on the rise. Using .5 on the chart it says:

CFM. Rise
453 N/A
1009 "65"
782 N/A
951 N/A
Click to expand...
The worse part with their recommended blower settings is that it wont even provide the “Rated Output” the manufacturer states it will.

This unit has an 80,000 btuh input, and at 96% efficiency, would give this unit a 76,800 btuh output.

The formula: CFM (airflow) x Delta T (temp rise) x 1.08 (constant) = Btuh Output

So given the manufactures numbers @ 0.50”wc, this unit will only have an output of 70,832 btuh
(1009 x 65º x 1.08 = 70,832 Btuh Output) when set to manufactures specs.

Only at 0.01” wc (unrealistic) will the chart numbers 1206 cfm and 57º get you close to the rated output
(1206 x 57º x 1.08 = 74,241 Btuh output).

The ideal setup on this unit should be 1200 cfm and a 60º rise.
 
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Discussion starter · #6 ·
rundawg said:
The worse part with their recommended blower settings is that it wont even provide the “Rated Output” the manufacturer states it will.

This unit has an 80,000 btuh input, and at 96% efficiency, would give this unit a 76,800 btuh output.

The formula: CFM (airflow) x Delta T (temp rise) x 1.08 (constant) = Btuh Output


The ideal setup on this unit should be 1200 cfm and a 60º rise.
Click to expand...
Thanks for some great info (although not so great for me).

So what the math tells me is that it's really a 92% unit in sheep's clothing as the unrealistic number came out to 92.8% (74,241/80,000).

And (I'm only guessing here but I used the .5 figures to compare) I'm really getting 88.5% (1009x65x1.08=70,832/80,000).

Your last line of "ideal, should be..." isn't even possible, though, correct? The chart shows I'm running at the highest speed available for heating (but the A/C can go up to 1260@.5), nor are any other speeds available as they say N/A (as I assume that slower speeds with put the rise beyond the acceptable range).

I think what ticks me off is that the 21" unit would be running a lot more air but is seeming about 96% according to that math and even the 17" 80% unit shows it's about 80% across the board as well, so why the 17" 96% unit starts as 92.8% and drops into the 88.5% is pretty misleading. Crap, even the 60,000 17" unit is 96% but not the 80,000 unit!!!

Granted, I'm better off than my 50 year old 80% that was 100k, but still, had I known the new 80% was 80% and the new high efficiency was doing only 88%, I might have gone a different route as I needed a liner for the water heater, etc. $500 here, $500 there.
 
#7 ·
What size A/C do you have? If you don't need the speed for cooling air flow the heating speed could be changed to that I would think. Most systems you can use any speed for cool as long as it is not the same as heat and visa-versa.
 
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#8 ·
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#9 ·
dan sw fl said:
__ WTH does _ that _ actually mean.?

https://hvac-talk.com/vbb/threads/2239353-CFM-for-A-C
Click to expand...
The Constant torque ECMs I have seen on furnaces are like a 5 speed motor, they have 5 terminals to plug the heating/cooling wires into. Usually the furnace comes from the factory set up for high speed cooling. If you have a blower that will move 1200 cfm on high but you have a 2.5 T A/C you don't need high speed for cooling. If that speed would work better for heating and it is not needed for cooling the heating speed can be high.

Does this make more sense?
 
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Discussion starter · #10 ·
BNME8EZ said:
The Constant torque ECMs I have seen on furnaces are like a 5 speed motor, they have 5 terminals to plug the heating/cooling wires into. Usually the furnace comes from the factory set up for high speed cooling. If you have a blower that will move 1200 cfm on high but you have a 2.5 T A/C you don't need high speed for cooling. If that speed would work better for heating and it is not needed for cooling the heating speed can be high.

Does this make more sense?
Click to expand...
The Goodman has dip switches instead of different terminals for speed control (at least the manual shows speeds via dip switches), but yeah, I'm around 1200 for cooling and 1000 for heat. Both are maxed out according to the book; 4 speeds for heat and 5 for cooling.
 
#11 ·
BNME8EZ said:
The Constant torque ECMs I have seen on furnaces are like a 5 speed motor,
they have 5 terminals to plug the heating/cooling wires into.

Usually the furnace comes from the factory set up for high speed cooling.
If you have a blower that will move 1200 cfm on high but
you have a 2.5 T A/C you don't need high speed for cooling.

If that speed would work better for heating and
it is not needed for cooling the heating speed can be high.

Does this make more sense? ... Gottcha.
Click to expand...
It's a W.A.G. approach unless there is detailed testing
and KNOWN heat loss and heat gains established by
calculations and verified by actual operations.

Proper Correlation of actual Energy Use to the specific equipment
AND local HDD and CDD data
Will provide much needed insights.
 
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