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Old 01-11-2007, 12:15 AM   #1
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Miller Mobile home furnace


I got a lighly used furnace at a mobile home recycler and installed it myself( used to be a hvac tech assistant gas furnace and ac work). It runs great fires up immediatly.It has a nice clear bright orangish/yellow flame with no soot. I just see the tips of the flames in the sight window. I am running #2 fuel(red dyed) with hotshot instead of kero.

It has a hot mettalic smell when the blower starts . It hasn't been used more than one or two seasons by the original owner. I had the blower off and cleaned it plus the top of the exchanger and the tubes.

I did the temp rise and found it to be between 90 and 100 degree . Specs are 70 to 100 degrees....I didn't want to drill a hole so I took the supply temp at the register in the bathroom 3 ft down stream and got 170/180 degrees...I don't remember the old furnace temp getting this hot , more like 120-140 at the same vent.. The old furnace burner ran for a minute then came on for another minute after the fan ran a bit..Now this one runs steady for three to 4 minutes then stays off while the blower finishes...Total cycle length of 12-13 minutes. It does this 3 times an hour when in the low 40's and 30's.

The stat is the same Honeywell setback one set at 4 cycles per hour. The old moc 80 was 67,000 btu in , this cmf 80 po is setup for 72,000 in.. The old one had a simular hot smell but not as strong even after they were cleaned.I have the fan set to the specs I found at nordyne.110 on 90 off and the hi temp is factory at 160. Alot of times the Hi limit kicks the burner off before the stat is santisfied..

The burner can be adjusted to run a little lower output than the old one or can be set for 90,000 btu's with nozzel and pump changes . It has aluminum ducts that really creak as the expand..Might this be a hot aluminum smell?. If the stat is set for 68 it's 71 when it's done

I figure the only way to get cooler air is to derate it..So I called the service guy. He comes out adjusts the air a bit, checks he pump and pulls the nozzel to check adjustments. He then tests for efficency and it is 79-80 percent..Stack temp 470 deg..Says everything ok even with the 160 degree hi temp kicking out.Says they are designed to run hotter and more efficient..Fan is on Hi setting even tho the speeds sound no different. He was there for 1 and 1/2 hour..$90..

Questions..What can I do to have the burner fire for less time or come on twice for shorter runs like the older one. The high temp air is incredibly drying even with the atomizing humidifier running...Will a different stat help..Should I pay to have it derated(Miller has a kit) I assume it is a nozzle and there is something that gets put in the pump included with the furnace..I watched the guy and could mark the setting of the nozzel and replace it..Could just replacing the nozzle to a lower gph work or must the pump be changed..We'l, I guess that is enough questions for now..

I just never had a metalic smell in my stick built homes with hot air furnaces. Last question: Would kero burn better or extend the life? Thanks for your comments....Happy New Year...God Bless..Kim

Last edited by hiskid1973; 01-11-2007 at 12:20 AM.
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Old 01-11-2007, 02:03 AM   #2
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Is the filter clean? returns and supplies open and clear.
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Old 01-11-2007, 02:06 AM   #3
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Yes..brand new filter...Only difference is a shutter to keep the ac from blowing in the furnace, the furnace blower keeps it open..
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Old 01-11-2007, 02:14 AM   #4
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You could install a lower GPH nozzle, but wait Carrierman will be back later see what he has to say. Oh yeah... It's not suppose to cycle on the Hi-temp limit
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Old 01-11-2007, 08:55 AM   #5
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Hi hiskid1973

Any time you are tripping limits, overheating metal, etc, on a forced air furnace means one of two things. The most common being low air volume due to restricted duct or plugged evap coil. If the system is equipped with air conditioning the first thing I would reccommend is to remove the evaporator door, fire the furnace up and see if you still trip the limit. If at this point you are still tripping the limit, your blower for some reason is not moving enough air. Could be dirty blower wheel or motor not running up to speed. However if it does not trip the limit, have the evaporator coil removed and thoroughly cleaned with water and a chemical coil cleaner. That should solve your problem. When you derate an oil furnace you have to make sure that the oil incoming pressure is regulated accordingly. It appears you only went up 5,000 btu's, the duct work usually will accomodate small changes, but you could be at the edge of your threshhold. Have them check this for you or you can do it yourself just be carefull.

Good luck
Rusty
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Old 01-11-2007, 03:31 PM   #6
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Thanks Carrierman..there is no coil, it hits the shutter for the package AC..The old furnace never had one. that is the only thing in the way..The blower is spotless and is three speed but all the speeds sound the same, I tried both Hi and med and their is no difference. this one is definitely more power as it comes rippin out of that first bathroom duct..The furnace is a little louder sounding.

I am wondering that even tho the temp control looks brand new it might be defective as the 160 degree cutoff yeilds 180 d..Once last eve it hit 200..I had to get oil along with the service so exta money for the next service call will have to come from next months check.

Or is it possible the Honeywell setback stat is defective and making the burner to long by not responding quick enough. Sometimes the stat santisfies before the hi temp, other times I hear the stat click 30 secs after the burners were shut off..

To keep it working at a safer level, I put a small self tap screw in the slot past the hi temp tip and have it kicking off with 160 d. coming from the bath duct. i know that isn't the best but it's working.

Thanks for the comments...K

Last edited by hiskid1973; 01-11-2007 at 05:32 PM.
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Old 01-11-2007, 03:49 PM   #7
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Hi hiskid1973

From what you are explaining here, it sounds like you will have to derate the heater. But before you do make sure there are no floor registers closed off, or that the louver you are talking about is not interfeering. If there are no problems with that you will definatley need to tune her down a bit. I am not sure the size of the area you are heating, but 60, 75, 90K are the most common mobile home BTU's. The higher the efficency the lower the BTU's needed for the job. Its real easy with the higher efficency units to cause overkill.

Good luck
Rusty
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Old 01-11-2007, 06:50 PM   #8
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Thanks Rusty..It is 950 sq ft..The old furnace was 64K but's out..This one is shipped at 72k and can go down to 60k and up to 90K. I guess you just can't swap nozzels..There is a little sleeve or something in a plastic bag taped to the pump, I guess it gets swapped too.. Thansk..Kim
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Old 01-11-2007, 08:17 PM   #9
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When you change your nozzel why cant you put a smaller gph (gallons per hour ) nozzel in?
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Old 01-12-2007, 02:24 AM   #10
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Quote:
Originally Posted by trollmastergeneral View Post
When you change your nozzel why cant you put a smaller gph (gallons per hour ) nozzel in?
I don't know. Rusty would this work..I would have no problem here, but I think you have to adjust the pump pressure..Rusty, I have below as a temp setup. Will this cause any problem.. I have a small self tapping screw to hold the hi temp at 140..It is working like the old one. It comes on and runs a bit, then fan running cools it enought for another short burn and stat takes it off. Has the 130/140 out like before. Thanks...God Bless..Kim
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Old 01-12-2007, 08:31 AM   #11
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Hi hiskid1973

You may be able to tune it down some by turning the fuel pressure down. Just be carefull when doing so, if you go too low you could cause it to backfire, you don't want a flame behind the retention ring. That would not be a good thing. The best way to derate one is to install a smaller burner nozzle and have the c/o and oil pressure set properly. As far as the fan limit, if it continues to trip it all the time it will stop functioning. The unfortunate thing about this is it always happens the day you cant get the parts.

Forgot this part. When you go to sizing burner nozzle you will need the number that is around the head of it. Delivan is real good about theirs, the last two digits on the Delivan tell you the nozzle size. Example being 98 next step down would be 95 etc.

Good luck
Rusty

Last edited by #CARRIERMAN; 01-12-2007 at 10:59 AM. Reason: Added information
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Old 01-12-2007, 08:33 PM   #12
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You should use a fuel presure guage to check the pump for proper presure. You can not turn down the presure unless it is to high.


buy using a smaller nozzel you can spray out less fuel therefore slowing down the flow and getting less heat.
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