furnace settings

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  #1  
Old 01-31-03, 08:02 AM
leftyone
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Question furnace settings

i have a new forced air furnace(olsen) my question is what are the low and high tempertures supossed to be in the air box..I have a thermoter installed above the a coil.presently the blower comes on at approx 74degrees and while the burner is running stays at approx 90 to 95degrees..im wondering if im under fired my blower is set on med high speed and the burner is set up to its lowest firing i believe a 65 tip..the present set up does heat the house nicely thanx for any info ps great site
 
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Old 02-01-03, 09:53 AM
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Question More info please.

leftyone:

You don't tell us much about your equipment.
For example what fuel or efficiency your unit is.
This info is necessary to be able to form an opinion on your question.
It is possible in a standard efficiency gas furnace the bonnet temps you are getting could cause flue gas condensation.

Refer to the Read-B-4 Posting anouncement at the top of this forum for what we need to know.

The temp sounds kind of low though.
Make sure you provide details on your house size and furnace capacity.
 
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Old 02-01-03, 10:36 AM
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If you have a fan control that is triggered by temperature and not a timer, the fan-on temp should be about 140 and the fan-off temp should be 110. The high limit should be about 180. Those temps are as measured right at the heat exchanger. If you have a thermometer up in the plenum, your readings will be different.
 
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Old 02-01-03, 05:37 PM
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blower speed

Temperature rise should be your determining factor for the desired speed tap. Look at the furnace name plate it should say something like 40-70F . you find the middle point (55) and add 5F to it(60F) this is where you should shoot fo, a little above the half way point...This refers to the return temp and supply temperature differences.
 
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Old 02-01-03, 05:41 PM
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blower speed

Temperature rise should be your determining factor for the desired speed tap. Look at the furnace name plate it should say something like 40-70F . you find the middle point (55) and add 5F to it(60F) this is where you should shoot fo, a little above the half way point...This refers to the return temp and supply temperature differences. Keep in mind, if the heat exchanger is sooted up, that means it is insulated, and won't readily give up it's heat to the air passing across the heat exchanger. This rarely happens with gas, but soot is common with oil fired furnaces.
 
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Old 02-02-03, 04:37 AM
leftyone
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more info

my heater is 86%eff firing i beleive 82000btu house is approx 1900 square ft pretty well insulated.the fan limit switch has four seperate settings on it...i appreciate all the responses this is a great site
 
  #7  
Old 02-02-03, 03:55 PM
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The fan cut in should be comming on after the temperature gets alot hotter, say 110F. If it cools down to 90 in less that 5 minutes, slow down the fan speed to medium, and monitor for 30 minutes. Does this take in outside air? If so, this may be why your supply temp is so cool. The return air needs contact time in order to get warm. Check your exhaust temperature also. It sounds like you could use a good cleaning and boiler tune-up and efficiency test. Have your oil man do the efficiency test before and after, it will only take 5 minutes extra to do the before test, this will tell you a before and after status. I'll bet dollars to donuts, you don't even have 80%, nevermind 86%...
 
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Old 02-02-03, 04:11 PM
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I don't know what the 4 settings could be. The three I gave you earlier should be set on the fan & limit control. What does the 4th one look like?
 
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Old 02-02-03, 04:13 PM
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Tips

The .65 tip you refer to doesn't tell you the heat output of the nozzle, only the gallons per hour at 100PSI, but #2 @ 140,000BTU/H X .65=91,000BTU/H, ... now if you look at the data plate on the furnace it will have a firing RATE...this is what you should go by. I would be inclined to go down to a .60 and crank up the pressure to match the firing rate per the manufacturer. Make sure to match the same pattern and angle, this is critical for best efficiency. Most oil people don't like using nozzles at the .50 range because they tend to clogg too easily. But you could and crank up the pressure for better atomization of the fuel. This tends to shorten the flame and lower the stack temp. This way, your fuel combustion is more complete in the combustion chamber(for the heat transfer) the smaller the fuel particles, the larger the surface volume area and air mixture for complete combustion.
So keep the pressure up and match the firing rate. 1/8" of soot will decrease efficiency 10%.
 
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Old 02-02-03, 04:16 PM
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4 pins?

I've never seen four, only three!
 
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Old 02-02-03, 04:17 PM
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Photo

How about a digital photo?
 
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