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Hot air furnace question

MaxMercy
MaxMercy Member Posts: 179
Questions at the end but a little bit of info. My best friend called me yesterday because he knows I know at least a little bit about oil burners. He had his 1988 Heil furnace routine serviced by a well known local oil company. He said it ran a few days normally and then suddenly started smelling up the basement, but no lockout. They came back and installed another nozzle which seemed to fix it but he wasn't sure if he still smelled anything or if it was in his head.

I asked him if he had the printout from the the combustion readings and he said they didn't do one.. (!)

I went up last night with my wet kit and took a look. It sounded fine and I didn't smell anything. It had an oil burner I didn't recognize, but it has the form factor of a Becket or Carlin at least. It has only one global air adjustment shutter, and it seemed open quite a bit. I took a smoke reading and got zero smoke, but the CO2 reading was about 7. I reduced the air a couple of times until I got the CO2 just under 10ppm but still at zero smoke, and left it there. It had a gross stack temp of 630F but the furnace room is partitioned from the basement and he had 10' run of the flue before it entered the chimney, so it may have been 75F around the furnace.

Questions: is a long flue run a bad thing for condensation? I didn't take a temp reading down the flue near the chimney (should have, thought about it on the way home) but by hand it certainly felt much cooler than at the furnace.

I also couldn't get a draft reading through the sight door. I got about .04" at the breech, but nothing at the door. Do hot air furnaces draw like boilers do?

What is the lifespan of furnaces? This is a Heil and is original to his house, which puts it just over 30 years. Time to think about an upgrade?

If so, is there a better brand of air scorchers that have a good efficiency and lifetime?

Are furnaces more efficient on one type of fuel than another? He's in the sticks like I am. Only options are LP, oil, and electric (out of the question).

Thanks.


Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,132
    I'll attack only the last question -- and the answer is no for fuel burning. If the burner is set up properly, either LP or oil will do just as well. Sometimes a big if, and it does also assume that the furnace can be fitted with the correct burner.

    Electric resistance is 100% efficient -- at the furnace. About 30% efficient overall in terms of fuel use. Heat pumps can approach the efficiency overall in moderate weather.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    MaxMercy
  • 426hemi
    426hemi Member Posts: 64
    Did you check for combustion gases at the vents a 30 year old furnace is likely to have a bad heat exchanger. If not you should have draft over the fire you need to adjust both the damper and air shutter to get it right sound One thing I have seen on furnaces is the door where the blower/air filter is was taken by customer to change air filter when running off or has a loose fit this will pull a huge negative pressure which will suck flame and or exhaust out the burner 
    MaxMercy
  • 426hemi
    426hemi Member Posts: 64
    It sounds like the furnace is dirty the heat exchanger has two clean outs with 3 in covers above the burner I put a vac on one and go in with a long blowgun on the other 
    SlamDunk
  • 426hemi
    426hemi Member Posts: 64
    630 deg stack temp is high and a flue temp drop of 550 degrees over 10 feet is all pointing to a choked furnace or negative pressure issue but since you have a good stack draft this all points to dirty furnace
  • MaxMercy
    MaxMercy Member Posts: 179
    426hemi said:

    Did you check for combustion gases at the vents a 30 year old furnace is likely to have a bad heat exchanger.

    I did not. I do not have a proper CO tester, but no fumes are obvious and my buddy has half a dozen CO detectors around his house, although I don't know their thresholds.

    The furnace *shouldn't* be dirty as he just had the local oil company clean it and service the burner.

    I'm not a pro and won't be doing any work on this furnace as it's not my own, but will do as much asking as I can on this forum for advice to help him out.

    He's pretty sure he's going to replace it this spring. The oil company who just cleaned it quoted him a price for the furnace plus changing out the A/C at the same time, which is why I was hoping some pros could offer some recommendations for a quality furnace.

    Thanks.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,356
    Best new furnace is a Thermo Pride.

    Any burner problem is magnified with a furnace as any basement smell including a combustion issue will likely get pulled into the return air ductwork.

    The furnace may be near the end of its life.

    What I do is with the burner off put your draft gauge in the peep hole over the fire and then start and stop the indoor blower motor several times while watching the draft gauge........the gauge should not move. If it does the HX is bad.

    Chances are the furnace has never been cleaned, they are difficult to clean and many toss in a soot bomb and call it a day.

    I would remove and clean the smoke pipe, clean the furnace and set the burner up.......sounds like you did improve combustion somewhat.

    Investigate the burner to see if a smaller nozzle can be used to reduce the stack temp.

    MaxMercy
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,322
    Maybe just the cleanouts were put back on correctly, or the gaskets need to be replaced.
    I hope that .04 at the breech was negative.
    Yes flue pipe construction is very important for proper draft. There are plenty of codes and guidelines.
    Generally:
    --Flue pipe same dimension from appliance outlet to chimney base, no reducing.
    --Flue pipe less than 10', pitched 1/4" per foot minimal.
    --TEPL of connector not to exceed 75% of chimney height.

    I'd also redo combustion readings with an electronic analyzer.
    Did anyone take a peak at the end cone?
    High stack temp can also be too high a draft, or too much combustion air.
    steve
  • MaxMercy
    MaxMercy Member Posts: 179

    Best new furnace is a Thermo Pride.

    Thanks for the recommendation; I'll pass that along to my buddy. He hasn't received the quotation paperwork for the replacement yet, but he remembers something like either "Williams" or "Williamson". Once he gets the quotation, I'll have better info.
    The furnace may be near the end of its life.
    That's what we sort of figured. The oil company tech suggested the same thing.
    What I do is with the burner off put your draft gauge in the peep hole over the fire and then start and stop the indoor blower motor several times while watching the draft gauge........the gauge should not move. If it does the HX is bad.
    The blower fan cycled a couple of times while the burner was running, but there was no change in the draft over the fire with the blower on or off. In retrospect, I should have taken a draft reading with the burner shut down as well. I know when my mom's boiler was plugged, I was getting a positive pressure over the fire but a negative draft reading of maybe -.01 when it was shut down.
    Chances are the furnace has never been cleaned, they are difficult to clean and many toss in a soot bomb and call it a day.
    Since they didn't do a combustion test either, it wouldn't surprise me.
    I would remove and clean the smoke pipe, clean the furnace and set the burner up.......sounds like you did improve combustion somewhat.

    Investigate the burner to see if a smaller nozzle can be used to reduce the stack temp.

    Seeing that the house was built in '88, it's most likely oversized like mine is ('93). But I just went up to take a look. If it was mine, I'd go deeper, but I'm not a pro. Sadly, I'm not sure the pro did his job either. But since the plan is to replace the furnace in the spring, he'll let it go through the winter. It seems to run fine and he's getting no fumes in the house.


    I hope that .04 at the breech was negative.

    Yes, negative. Sorry.


    Generally:
    --Flue pipe same dimension from appliance outlet to chimney base, no reducing.
    --Flue pipe less than 10', pitched 1/4" per foot minimal.
    --TEPL of connector not to exceed 75% of chimney height.

    He's close to 10', although I didn't measure it. It's level at best, I didn't see a pos pitch at all, although I didn't check with a level. I'll have him do that.
    I'd also redo combustion readings with an electronic analyzer.
    You would think the oil company would have done this. I mean, this is a big company with a good reputation. My buddy did say though that the second guy who replaced the new nozzle that failed was their head installer and really seemed to know his stuff. Still he either eyeballed it or just replaced the nozzle and went on faith. If this was a new furnace, I'd advise my buddy to have them set it up properly, but since it's likely to be replaced sooner than later, it won't really matter.

    BTW, I don't know if all furnaces are like this, but the flame on this furnace can't be seen directly through the sight hole like it could on an oil fired boiler. It seems like there is a metal "igloo" inside with openings on the side. The light of the flame could be seen in the firebox area, but not the flame directly. I don't know how anyone could eyeball the combustion unless they were perhaps monitoring the cad cell readings...

    Thanks everyone.
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,322
    Yeah you can't see the flame. All the more reason that it must be checked/tuned/set up with an analyzer.
    steve
    SuperTech426hemi
  • SlamDunk
    SlamDunk Member Posts: 1,111
    High excess air will tell you if you have a cracked hex.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,356
    -,04 at the breeching sounds about right you should have -.02 over the fire.

    Yes, Williamson makes oil fired furnaces but Thermo Pride is the best
    MaxMercySuperTechjimna01
  • Kickstand55
    Kickstand55 Member Posts: 32
    I've seen many failed heat exchangers with units over 20 years old.
    Safety First! The heat exchanger needs to be checked even if the furnace has to be disassembled. Or, better yet, due to age, replace it with a well known brand name with a heavy heat exchanger especially if the basement is damp. Have the chimney checked by a registered chimney sweep. It may need a stainless steel liner.
    Have it thoroughly cleaned and serviced every year right after heating season, not in the fall.
  • SuperTech
    SuperTech Member Posts: 1,691
    I think Thermopride makes the highest quality furnace available, oil or gas. 30 years is way too old for a Heil furnace, Thermopride is the only furnace that I wouldn't be concerned with being that old. Williamson is ok, I would definitely avoid anything by the manufacturers that sell a lot gas furnaces,  Carrier/Bryant, Lennox, York/Luxaire, Rheem/Ruuud. 
    STEVEusaPA
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,397
    Also agree that Thermopride is the best oil furnace available. they are still building them with the copper paint on the heat exchanger and the Heat Exchangers are thicker metal.

    40 years ago they were offering a lifetime heat exchanger warranty. long before the competition had a 20-year warranty. I have installed warranty heat exchangers for 2 different clients over the years. They are well built!
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    SuperTech