Gas Hot Air Furnace / Blower Speed??

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Hi,
I need some thoughtful thoughts about blower speeds.
First the facts: I have a Sears 105,000 BTU / 84,630 BTU natural gas furnace in a 1,900 sq ft 2 story house.
The thermostat is a Honeywell programmable with "fuzzy logic".
The blower speed is currently set at "Med-Lo" which is about 1,100 cuft/min or 70% of maximum (1,500 cuft/min) volume.
Question: Would the furnace be more efficient at a higher blower speed?
If so, is there a benefit from adding an outdoor temperature sensor to trigger the higher blower speed when the outdoor temperature falls below, say 45 degrees F.?
Any thoughts will be appreciated.
Tom
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Don't fuck with it. You might blow yourself up.
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below,
Stay with alt.hvac where your comments and wiseass remarks are the norm. This forum is for helping out not competing with the rest of the gang trying to show just how dumb you are. BTW, have you ever shown your family the type of trash you spew out at people?
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Leave it alone...higher for cooler...slower for warmer...oh..whats the static pressure for that unit, and whats the heat rise set to?
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Blower Range settings: ON 125 and OFF 90
Don't know the actual static pressure, manual gives .2 to .5 range
I'm not looking for trouble, it works well, just ruminating if it could work better - more efficiently.
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Don't fuck with it unless you are a trained technician.
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the thermostat that calls for heat is best thought of as an on-off switch where the demand for heat is requested. could the factor of the house's heat loss might be better handled with a variable speed blower? remembering the comfort of your home in winter requires a balance of temperature and humidity and sufficient oxygen from air changes. if you blow the heat out of the plenum too fast into the house you will not enjoy even heating of a close temperature differential of one degree. if you blow it out too slow the house will drop below the desired temperature. get a digital thermometer with high low memory and monitor the temperature at the thermostat to see how your range varies, and determine a course of action to zone your home so no room gets excess heat.
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Thanks for your thoughts.
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This is Turtle.
What you need to do is get a Service tech out there and set your heat Rise to about 50 degree F and find out at what speed it should be at. heat Rise is the difference between the air going into it and the air coming out.
Now speaking off the hand and no facts to stand on. Set it up higher and see how it does but you will have to try to measure the heat rise to not get it too low. 29 degree F or less would be too low and nothing over 65 degrees F. differencial or heat rise.
Now speaking off hand here , if you can increase the blower speed it will get the heat out to the rooms faster and then cut off faster. So it would help a little to speed the blowers.
Now the out door thermostats is for another post here after you get this right.
TURTLE
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Thanks TURTLE, I'll chew on these ideas. Tom
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Now the fun part, measure blower amp draw where it is at, and at your desired setting, , calculate run time , at present and new setting, run your Kwh costs to reflect your increase in kwh and decrease in run time if any. You just lost in electricity costs. For most of the US Kwh are more expensive than NG so you are a net looser there. Oh did you increase efficiency of the Ng side, , im sure not enought to matter or offset the higher Kwh to run the blower. Say your blower takes 375 watts and runs 8 hrs a day avg and cost is .125kwh, mine is, your present avg cost is 9 kwh a day or $33.75 a month.
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The heat exchanger will probably be more efficient at the higher airspeed.

...8hx375W = 3 kWh, ie 3x$0.125/kWh = $0.375/day or $11.25/mo.
If you increase the airflow from 1100 to 1500 cfm, the blower may use (1500/1100)^3x375 = 951 vs 375 watts, according to the fan laws. At 1100/1500x8 = 5.9 hours per day, it might use 5.9x951 = 5.6 kWh/day or 5.6x0.125x30 = $20.92/mo.
Nick
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If you only had a clue...
errs again:

More efficient? Maybe not.

You are obviously overeducated.
The manufacturers specify a temperature rise for each line (and size) of furnace. Go out of these lines, you void any warranty. Period. These temp rise numbers are to get the most heat and longest life out of the heat exchangers.
Get a life.
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Don't spew this shit in this group. Take it to alt.hvac where it belongs. We only want fantasy fairy tale advice in alt.homo.repair.
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Oscar_Lives wrote:

Let us know when you attain puberty, ok?
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minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.
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You will know when you get a mouthful.
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Tom,
1) What is your temperature rise? Should be 40 to 60 degrees. If you increase air flow, your gas efficiency will go up a little as you remove more heat from the heat exchanger. Your flue temperature will go down slightly, increasing combustion efficiency slightly. The electric efficiency will go down a little as you will use more electricity to move a little more heat. With a lower temperature rise, your supply air temperature will go down, which may reduce your comfort. Now your furnace supply air will feel like that from a heat pump.
2) How did you measure the air flow? What instruments did you use?
There are tradeoffs to everything you do.
Stretch
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He probably actually read that info off the wiring diagram.

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yep...
measure the hot air temp near the furnace.....
stick a thermometer in the duct somehow...
if it is much over 120 deg F after the furnace has reached full temp... then a faster blower may be a good thing for you.
But if you don't REALLY know how to re-wire it, you can create problems...
make sure the saftey function still works,, if the furnace overheats, the furnace must turn off and the blower turn on...
Mark
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Now...if its got an older model, you know the blower wont even start to about 160 give or take a couple of degrees...right?

Not on all models..

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