Increasing stack temperature

zeke

I am wondering why over the past several years following a tuneup of my 14 year old oilfired furnace, the CO2 level remains 11% but the stack temperature has steadily risen from 350 ( in 1998) to 650. Could anybody tell me the possible causes?

Also I have never seen a tech test for CO. Am I missing something?

Thank you for your reply.

Maine Ken

What kind of "tune-up"? Oil side only? Cleanout ports, flue, breech?

Steamhead

It's probably sooted up

Bet they didn't brush it out. Have someone else take a look at it.

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Pinball

One more thing, If it is a steel boiler with baffles, are they still there?
I have seen some "techs" clean a boiler and "forget' to put the baffles back in the unit. or are they have slowly rotted out to the point where they are almost non-existant.
Either way, have somone else do a real tune-up complete with a bacharach kit or equivelent. Test for First and foremost, DRAFT, smoke, CO2 and net stack temp.
Al

Tony Conner_2

Could Also Be...

...scaled-up on the water side. Do you have to add much water to this boiler?

kevin coppinger_4

its hot air guys.



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Bill Nye_2

could be

different nozzle[bigger] air setting, draft, technician, how long the first guy vs the second guy left the thermometer in? Restricted return air flow....blocked register or dirty filter? Adequate ductwork

zeke

Thank you all for your response.
To clarify things.It's a forced hot air system and I just moved in. The test results are posted on the furnace panel, with different technicians, so I can't answer the nozzle question or the thoroughness of these tuneups. However, I have personally verified the current 650 degree stack temperature reading. The last tuneup was in April. Can I do anything now as a DIYer to lower the stack temperature or should I wait for
the next tuneup, since the estimated efficiency as recorded is 81% ( I wonder how good this number is)?

Mark Hunt

Over-fired or


insufficient air flow across the heat exchanger.(Air flow would be my bet)

Make and model of the unit would be helpful, as would a picture of the duct system.

Hard to diagnose over the I-net.

Mark H

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zeke

Mark,
Thanks for answering.
The unit is a carrier 58HU085 which is an upflow system with an A/C addition.; the main supply duct is 24x10 and return duct 18x10 into the plenum. The filter is 20x25 and was recently changed. I also measured the hot air leaving the heat exchanger at about 110 to 120 deg. using a 100-800 range temperature dial indicator.

Mark Hunt

Is the


burner operating on high limit? That would be on a call for heat, the burner fires, fan comes on after a delay, burner shuts down but fan continues to run and the call for heat is NOT satisfied, burner fires again.

I'll look up the specifics on that unit.

Mark H

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zeke

Mark,
I think on a call for heat, the burner starts and the blower doesn't come on until 140 is reached and both fan and burner are on until setpoint is reached when burner shuts down, after which fan continues until temp falls to 100 deg. The high safety limit is set at 180.
Thanks again.

Zeke

Ed N.Y.C.

Hi Stack

Zeke I am assuming that 650 is a net not a gross, if so than you would be in the range of 16%co2. Sounds like a bogus result. Stacks way too high,should be approx. 450 gross and co2 approx. 11%. Hope this helps. ED N.Y.C.

Tundra

Another thing for your check list. Make sure the fan is clean. If it is loaded it will significantly affect the amount of air over the heat exchanger.

zeke

Ed,

The 650 is gross, so the net is probably 580.And the CO2 has been consistent at around 11% over many years. Also the blower looks clean.
What about increasing the blower speed? It may not be on its highest setting.

Thanks for your remarks.

Zeke

zeke

Tundra,
Sorry I posted under Ed's reply. The blower looks clean.
Thanks

Zeke

Ken D.

High Stack

A number of things cause a high stack. Burner fan must be clean. Blower fan must be clean. Belt tight?. Registers open? Proper nozzle? Proper pump pressure? Air and oil filters clean? Pump strainer clean? Baffles ok? Heat exchanger clean? Good combustion? Burner properly adjusted? Draft too high? Combustion chamber OK? A unit with improper nozzle or combustion can require too much primary air that increases stack temp. Blower speed and rotation OK? Stack temp. gauge accurate? One other remote possiblity- I had a customer once that had miles high stack temp. and terrible combustion. Turns out he would put his used motor oil from his car into the oil tank. I assume you have good fuel. Ken D. with a capital K.

A. mitchell

dirty heat exchanger

an 1/8 inch of soot is equal r-30 in your home my guess would be have the unit propley cleaned as the soot build up will result in poor heat tranfer and generate high stack temps

Robert O'Connor_6

What Brand

furnace is it?

Regards

Robert

ME

Jim Davis_3

Air Flow

If your air temperature is only 100-120 degrees your blower is running too fast and this will cause your flue temperature to be 50-75 degrees high. Normal flue temperature for oil should be 490-600 dergrees gross.

zeke

Just saw a typical tuneup on my neighbors furnace (similar to my foced hot air) and the technician looked at me like I was nuts asking why he doesnt clean the heat exchanger; said he never heard of doing this.
What do you professionals do?

zeke

Just saw a typical tuneup on my neighbors furnace (similar to my foced hot air) and the technician looked at me like I was nuts asking why he doesnt clean the heat exchanger; said he never heard of doing this.
What do you professionals do?

zeke

I dont get it. If the blower is blowing more air across the heat exchanger my logic says you should be transferring more heat and therefore LOWERING the stack temperature, not increasing it.
Where did I go wrong?