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Old 01-01-2013, 07:44 PM   #1
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down sizing an oil burner nozzle


A year ago I had a 100K btu Tappan (Nordyne) O5LD low boy oil furnace installed. it replaced a 29 year old Magic Chef 100K. The old furnace on the coldest days ( -10 to -15 f) would burn about 50% of the time. It is my understanding a properly sized furnace should run almost 100 % of the time in the coldest weather, therefore the old unit was oversized. since the new install we have not had any really cold weather to put the new unit to the test.

Question, should I have an undersized nozzle put in when I have its 1 year service??? I am really happy with the new unit, quiet and it appears to be far efficent as my oil consumption is down.

Question 2. I have a manual thermostat which I turn off when I leave the house and turn on when I return. This gives me longer run times, which I understand should be more efficient. So far this season with outside temps in the mid 20's overnight the house drops from 67 to about 59. upon firing the burner in 1 hr of constant burn the temp is at 70. about 10 degrees / hour increase. should I continue to shut the furnace off and go for the longer burn time?

The house is in Southeastern Ma., 2400 sq ft. lots of glass. half of first floor is on a slab with a cold tile floor.

thanks for any suggestions and thoughts.

bernie

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Old 01-02-2013, 04:38 AM   #2
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down sizing an oil burner nozzle


Is that 100,000 BTU input or output. Input, leave it be, output down fire it.

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Old 01-02-2013, 08:24 AM   #3
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down sizing an oil burner nozzle


thanks Beenthere.

just looked at the furnace. I was wrong on the BTU's. It is 117K output, so I guess my choice to downsize nozzle is correct. I will go with one size for now and see if I am happy.

anythoughts on burn time. I do like turning thermo up and down as needed, using wide swings in temp.

Where in Pa. are you located? originally I lived in Bucks Co. near Phila. lived in Mass for almost 40 years now.

again thanks,

Bernie
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Old 01-02-2013, 02:36 PM   #4
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down sizing an oil burner nozzle


I'm in Lancaster. So you didn't live that far from me.

You should be able to go down to a .85 nozzle without any problem.

My furnace can do an 11 degree temp increase in the house in 70 minutes when its 25 outside. Its fired so I can maintain 72 when its -5 outside.
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Old 01-03-2013, 09:05 AM   #5
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down sizing an oil burner nozzle


thanks for the advise.

just an update, this morning it was 5 F and now 10 F (outside)

When I started the furnace this am it was 53 after 2 hr 15 mins of burn I reached 73 inside. that is a 20 degree rise or about 7 mins / degree rise. the nozzle down grade seems in order. will mention when I schedule my tune up.

Lancaster, home of my dewalt radial arm saw (circa 1957 MBF).

Beenthere, thanks.

bernie
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Old 01-03-2013, 01:00 PM   #6
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down sizing an oil burner nozzle


When you gentlemen give the output rating of your heating system, do you usually mean the DOE or net IBR? The values between these two differ by quite a margin. I was interested because my system's DOE is 148K and IBR is 129, in my 2,300 sq ft house. That being said, I run a radiant system, not forced air. It's probably oversized.
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Old 01-03-2013, 01:34 PM   #7
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down sizing an oil burner nozzle


Bernie..IBR is the output of the boiler and heating pipes factoring losses from same . My understanding is that DOE does not calculate losses from boiler jacket and piping bercause, after all, the heat is still inside the building envelope and contributes to the heating.

Did you downsize the new boiler? If so, you shouldn't have to downsize the nozzle. But, as Been There says you CAN downsize to .85. Too much downsizing can result in condensation in the flue gases creating sulphuric acid and premature failure of chimney liner/furnace flue.

As to on off cycling. I have read studies that stated that a drop of 5 degrees F is optimal for energy savings. I believe that running the furnace on extended "on"cycles might result in excess stack losses as the flue and chimney may get a little over heated. It's a fine line either way. I have learned that ensuring a well insulated building, good windows and limiting drafts/open doors/windows is a far better contribution to higher efficiencies.
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Old 01-03-2013, 01:52 PM   #8
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down sizing an oil burner nozzle


tech pappy,

right you are about the last paragraph. short term, not much I can do there. for a 1986 house it is not bad. 6" walls, 12-16 " fiber in attic. windows are standard thermo pane( 3 sliders, 3 skylights, 8 casment windows, 1 bay window,and 24 double hung.) a lot of glass. 500 sq ft on ceramic tile on concrete slab (unknown perimeter insulation under tile).

the 117K output value is on a tag on the furnace. (same size as the original furnace.) the beckett burner has a 1.00 nozzle. final call will be by the service tech.

the switch over was a direct switch with no calculations. I had heat exchanger failure in progress and this unit was available for immediate delivery. had to be a lowboy because of ceiling height clearance.

this furnace is the quietest furnace i have ever heard.

bernie
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Old 01-09-2013, 03:48 PM   #9
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down sizing an oil burner nozzle


Tech just left. furnace was clean as a whistle. he replaced a 1.00 70 B nozzle with a .75x80xA. previous stack temp 520 now 500. previous breech 450 and new breech still 450. efficiency went from 82.5 to now 83 %.

I will see how this goes. He felt .75 with a stack temp of 500 is a good place to be. Time will tell. any thoughts.

thanks,

bernie
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Old 01-09-2013, 04:07 PM   #10
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Hmmm, the breech temp is lower then the stack temp.
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Old 01-09-2013, 05:35 PM   #11
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down sizing an oil burner nozzle


Beenthere,

I may have(did) misspeak. the new tag says "ambient 500, breech 450" the original install tag is "gross stack 520, net stack 450" Does that sound right?

Thanks,

bernie
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Old 01-09-2013, 05:49 PM   #12
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Ambient is the temp of the air that it is using for combustion. that would be your basement air. Guessing he meant ambient 50. That would be ok.

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