Barometric damper swings & smokes when furnace starts


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Old 03-20-11, 09:38 PM
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Barometric damper swings & smokes when furnace starts

Hello!

I've been following the HVAC forum for a while and decided it was time to join! I have an interesting issue but before I explain, here are my specs:

House:
Upstate NY, 1920s saltbox, 2 floors plus walk up attic
Furnace:
Bryant 369A forced hot air oil furnace, 12 years old
Beckett AFG, DS902, F3 Head
Nozzle .85 x 70B (same nozzle size for all 12 years)
Oil Tanks:
Two(2) 275 gal, each has filter, tee after filters, gravity fed to furnace
Chimney:
Selkirk Metalbest UT 6" ID/8" OD, ~ 29' from basement to peak, with cap, oil furnace is only appliance
Flue pipe:
6" galv, 2 elbow before chimney tee, straight run 7-8'

My specific issue started after I replaced my block chimney (16" block w/ 8" square tile) with a shiny new 6" ID Metalbest chimney. When the furnace starts, the barometric damper will swing wildly and little puffs of smoke will exit it for ~ 1min until it smooths out (little puffs, not a puff back!). The issue is more pronounced on wet, warm days (40-50F) than on cold, dry days (< 30F). Once it runs for bit (5-10 mins) its very smooth and I get the following specs:

Draft over fire: -.02 WC
Draft at breech: -.04 WC
Smoke: trace, almost Zero
Pump Pressure: 100 PSIG

At first I thought it was coincidence that this issue started after I replaced the chimney, but I've been through my ENTIRE furnace system and nothing has made any difference except for one thing. On a hunch (ok, I'm desperate) I bumped the oil pressure to 110 PSIG & tuned it accordingly. Now the swinging & little puffs of smoke appear to be less on start ... or the fumes are getting to me!

So my question is ... without changing the chimney to an 8" ID or adding a draft inducer, can I tweak the furnace to reduce this start issue? Such as:

Change nozzle sizes & pump pressure?
Add a delayed open solenoid valve?

Any help is greatly appreciated. Thanks in advance!

-Chris
 
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Old 03-21-11, 08:23 AM
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Chris, welcome to the forum.

It sounds like you've learned a lot. Good job. I think I'd start with a delayed opening fuel solenoid, presuming the electrodes are set properly (5/16" above nozzle center, 1/16" ahead of the nozzle face, 5/32" apart, & pointed) & the ignition transformer is strong.
 
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Old 03-21-11, 09:54 AM
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Grady,

Thanks for the quick reply! The electrodes are new & per the spec you listed (5/16" above CL nozzle) The original Beckett manual listed 7/16" above CL, but I assumed they updated that number. Transformer is also new & strong ... weak/delayed ignition was one of my first failed paths. I'll order the delayed opening fuel solenoid and let everyone know the outcome. Thanks again!

-Chris
 
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Old 03-21-11, 10:24 AM
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Just thought of something else before you order the valve.

Inspect the burner head for any cracks or broken supports.
 
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Old 03-21-11, 03:30 PM
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oil and chimney

all things you have done so far are good...I would ad....if you continue to have problems,you could downfire to a slightly smaller nozzle.....another thing that I like is the electronic transformers that put out higher voltages than standard ones,especially on initial start-up.
 
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Old 03-25-11, 08:02 PM
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No Luck So Far

Grady & seabee570,

Thanks again for the quick replies. I've pulled the burner numerous times and did not notice any mechanical failures. Also, I recently replaced the transformer with an electronic one.

So I ordered the valve and because I didn't think the 4 sec delay (built into the harness) would be long enough I ordered a new oil primary with selectable 15 sec valve delay (Honeywell R7184U1004). To my utter surprise ... NO CHANGE. I'm getting used to the disappointment now

So, I'm off to the local HVAC store in the morning to purchase some new nozzles. The current nozzle is a Delavan .85 x 70B. I'm thinking of buying a small assortment:

.85 x 70A, W ... keep pressure at 100 PSI
.75 x 70A, B, W ... increasing pressure to 130 PSI

Any thoughts on these? Thanks in advance!

I was slow responding to your posts because of another issue I had. About 5 weeks ago I smelled something burning ... ended up the upper limit switch had a slight overheating issue! The rivet joint on one of the connectors had begun to melt the circuit board material and burn the paper backing. I took care of that problem and a few weeks later, the furnace stopped working but the blower ran continuously. Had a tech out to the house and he thought it was circuit board related. While we checked for power at the oil primary the burner kicked on ... figures I was going to order a new ST9103A Electronic Fan Timer, but they suggested I save my money and wait for the problem to occur again.

Fast forward to the night I installed my shiny new oil valve & primary. Valve installed ... primary installed ... turn on furnace ... nothing! I suspected the rough looking spade connector on the limit switch wire that smoldered, so I cut it off & replaced it. Checked the cut off end ... poor continuity. "Great!" I think ... turn on furnace, nothing I continued to check for continuity and voltages and didn't find anything unusual. At that point I decided to pull pull the Fan Timer board. When I turned it over I found my problem. The solder had melted off one of the limit switch wire contacts so the Fan Timer thought one of the limit switches had opened! Re-soldered the joint & the furnace was back in business!

Hopefully this info can help someone else with similar problem!!
 
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Old 03-26-11, 05:33 PM
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Wishing I didn't downsize the chimney!

The HVAC store didn't have all the nozzles on hand, but they at least had the .75 x 70B. Nozzle installed, pressure adjusted (for now) to 120 PSI and furnace tuned. Sounds a little quieter, but still puffs at start-up Tomorrow I will reduce the pressure closer to 100 PSI & see if that helps any.
 
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Old 03-26-11, 06:16 PM
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Here is some information which may be of some help.
http://www.docs.hvacpartners.com/idc...s369a.70.3.pdf

That same furnace is sold under the Tempstar label & having worked on some I can tell you they can be a bear. Certainly no picnic to clean. Whomever came up with the idea of a multi-position oil fired furnace needs to be shot with sh** & hung for stinking.
 
 

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