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  1. #1
    Join Date
    Nov 2004
    Location
    Howell MI
    Posts
    167
    I've been in the trade now for a while, and it just seems to be that propane will destroy any brands heat exchanger in 7-10 years. Is there any explanation for this? Some say its the "smell" they add to the gas, some say it's not set up right......well, after replacing a few, and seeing that gas pressure, temp split is correct what does that leave? Are the new style exchangers just built that cheap? Then you got manufacturers that have known problems with their furnaces secondary exchangers plugging up, so you get a new furnace that will plug up in the next 10 years! Gotta love them ENGINEERS!
    Is it Friday yet?

  2. #2
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,950
    There's a lot of moisture in LP gas that wrecks havoc when gas pressures are not stable.

    Since LP is not a very stable gas, even the best setup can have trouble on cold mornings or long off cycles. For this reason I highly recommend a low pressure cut-off switch be installed on all LP furnaces.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  3. #3
    Join Date
    Feb 2004
    Posts
    2,597
    Originally posted by RoBoTeq


    Since LP is not a very stable gas, even the best setup can have trouble on cold mornings or long off cycles. For this reason I highly recommend a low pressure cut-off switch be installed on all LP furnaces.
    robo, can you elaborate? what would provide the fuel in this case? i'm, assuming cold temps here.

    my mother has lp at a house not relly visited in the winter months. stat is at 55. yet when i was there last the burners were rusted. i didn't have my tools to check pressures so cannot give that info. and when i say rusted, i mean badly.

    6 year old rgra06, in a crawl, 2 piped, and yes, draining outside.

    not alot of lp in my area, and the few i've seen do not look like this.

    i'm curious about the switch.

  4. #4
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    The old inshot burners on Rheem are really bad for rusting with LP gas. The new burners have a curve and do not rust.

    Karst means cave. So, I search for caves.

  5. #5
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,950
    What happens on cold mornings, cloudy days or when there has been a long off time is that the LP in the line cools down, reducing its pressure.

    When the furnace calls for heat and the gas valve opens, the LP pressure may be down to 3 or 4 inchs water column of pressure rather then the 11" or so that is required. With this low burn a lot of moisture is produced in the initial section of the heat exchanger as well as on the burners. This condition can persist for several minutes each firing.

    With a low pressure cut off switch, as soon as the LP pressure drops below 6" WC, the switch cuts off power to the valve allowing the valve to close which allows the pressure in the LP line to stabilize. On the next firing, the LP has already built up the needed pressure to not underfire.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  6. #6
    Join Date
    Apr 2005
    Location
    Boulder,CO.
    Posts
    552
    Billva you said 55* setpt check your heat rise I'd guess 30-50 your raining inside your heat exchanger thats my guess. Raise the setpt problem solved, I can't help you on extra cost for the fuel though.

  7. #7
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    Thanks Robo, I have done quite a few conversions on Heil furnaces and they require a low pressure switch on conversion. Often wondered the true purpose of the LP switch. Thought it was in case the tank was getting too low so it would not do a delayed ignition due to low pressure. Thanks for clearing that up.
    "Go big or Go Home"

  8. #8
    Originally posted by RoBoTeq
    the LP pressure may be down to 3 or 4 inchs water column of pressure rather then the 11" or so that is required.
    How is the regulators allowing this to happen?

  9. #9
    Join Date
    May 2005
    Location
    Western Kansas
    Posts
    267
    Just guessing here, but the reason the regulator doesn't stop it is because it's limiting anything above 11" wc....makes a bit of sense after thinking about how many times I had to shake a propane torch on a 0 degree day to get much fire out of it....I'm curious to hear more on the regulator part myself

  10. #10
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    Originally posted by jultzya
    Originally posted by RoBoTeq
    the LP pressure may be down to 3 or 4 inchs water column of pressure rather then the 11" or so that is required.
    How is the regulators allowing this to happen?
    Low input pressure.
    If more government is the answer, then it's a really stupid question.

  11. #11
    Originally posted by mark beiser
    Low input pressure.
    I wouldn't think that would be a problem, till it got well into the negative figures...



    0 F = 24.5 PSI which is (1 PSI = 27.7" wc) 678.65" wc


    [Edited by jultzya on 11-11-2005 at 02:54 AM]

  12. #12
    Join Date
    Jun 2003
    Location
    New Hampshire
    Posts
    2,666
    I've never seen this problem with excessive rusting. And I have never seen a problem with low pressure on initial firing of an appliance even on cold days.
    It may have something to do with some installers not installing adequately sized above ground tank(s) for the coldest days (underground tanks are based on a warmer exposed temperature), proper regulators and piping to match the load. All this is done with using NFPA sizing charts. You should be schooled and licensed to do initial setups. Also proper evacuation and methanol methods must be used before putting a new tank into service. If all this is not done correctly then this is an endless series of service calls until all of the above are corrected.
    I have seen problems with tanks not being properly methanoled. The result is pulsating flames due to moisture in the gas (similar to an improper air/fuel ratio). Methanol then injected into the tank will solve this problem using approved methods. The REGO propane regulator booklet will tell you how much methanol is required for the tank used.

  13. #13
    Join Date
    Apr 2005
    Location
    Chicagoland
    Posts
    211
    I've been told also the LP gas is
    more acidic than Nat.gas-
    Don't know if theres any truth to that theroy.

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