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Thread: intermittent vs standing pilot

  1. #1
    Join Date
    Nov 2005
    London, Ontario, Canada
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    intermittent vs standing pilot

    I would like to hear a salesmans perspective on the benefits of the intermittent pilot system for the North American climate. Help me to understand.

  2. #2
    Join Date
    Aug 2004
    S.E. Pa
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    Cool Standing pilot versus IPI or electronic ignition

    First of all, remember there are two primary functions these systems perform:
    -flame proving

    As for flame proving, a standing pilot uses heat to generate electricity that tells the valve, "hey, we've got flame! Let the gas continue to flow" or "Oops!, Shut off the gas-no flame! Without an open flame, a fireplace becomes a bomb so we must "prove" there is an open flame to burn up whatever fuel is in there. When the flame hits the tip of the thermocouple (please note: there is no R on the end of thermocouple), the Seebeck Effect generates about 25-30 millivolts dc from the two dissemilar metals as long as there is a 400F temperature differential btw the hot junction and cold junction. This voltage is applied to an electromagnet at the back of the valve, which holds the valve open against a spring. If you lose your pilot flame, the voltage drops, therefore, the field on the magnet collapses causing the spring to slam the valve shut. The flame does double duty to ignite the main burner when there is a call for heat. Heat driven mechanical system.

    With an Intermittent Pilot Ignition (IPI), Hot Surface Ignitor (HSI) or Direct Spark Ignition (DSI), you do not use heat to generate voltage to power an electromagnet for flame proving. Electronic ignitions use ions in the flame to conduct an electrical signal to tell the control module "got flame" which in turn sends a signal to the valve to allow gas to flow. Should the signal be interrupted for a specified time, some units will try automatically to reignite for a short trial before going into lockout. You must know your system's timings. What can disrupt the signal? Anything that distorts the flame. DSI and HSI use the burner flame itself for flame proving while IPI incorporates a pilot flame that only burns as long as the main burner has a call for heat. Therefore, when there is no call for heat, none of these three types burn gas (except for one certain system from HHT that can convert an IPI into a standing pilot called their Cold Climate feature). If you get downdrafts, strange air circulation patterns within the firebox, venting anomalies, low gas pressure, etc. all can influence the flame pattern enough to lose signal.

    All electronic ignitions use a principle called "flame rectification". An AC signal is sent to the flame via a flame rod. If this rod is properly positioned, the flame is properly shaped to where it engulfs the flame rod, not with heat but the outer mantle where the ions are active, and the burner is very well grounded and has a mass at least 4 times that of the flame rod, positive ions will form a bridge of stepping stones through the flame for one half of the electrical signal to cross. This form of discrimination means one half of the AC sine wave makes it across so we say the signal gets "rectified" into a DC signal that the control module is set to recognize in microamperes (millionths of one ampere of flow). It is the amperage--not the voltage of the signal we care about. Too much or too little and you can drop out.

    Main burner flames are more prone to flame distortion than a pilot flame believe it or not so if you incorporate this function at the pilot, your reliability should go up. In practice, it has. The HSI has one distinct advantage over the IPI or DSI--it is more reliable for systems with a lot of air flow through them. An IPI would not work well on a clothes dryer or some furnaces.

    A standing pilot means continuous consumption of at least 600-800 BTU/hr of fuel 24/7. Most IPI pilots consume about 1,200 BTU/hr. input while ventfree ODS pilots are usually around 1,600. Annualized, that amounts to at least 5,256,000 BTUs/ year or up to 14,016,000. To figure the cost of this, obtain your local fuel cost per therm then apply times 5,256 on the low end and 14016 on the high. That will give you the annual cost of running a pilot alone. States like Calif. have banned standing pilots in all new equipment. I'm still trying to find out how they plan on installing vented logs in all the woodburning fireplaces since there are only one or two electronic ignition vented logs on the market right now.

    I don't think the issue on ignition choice is so much regional as it is reliability and energy conservation. The IPI is more expensive but more reliable overall. While a standing pilot works during an electricity outage, more and more IPIs have a battery backup system. These typically run off 'D' cell flashlight batteries or maybe a 9 volt. They don't need car batteries because the amount of power they consume is very low.


  3. #3
    Join Date
    May 2005
    Madison, WI
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    For the units we sell, IPI is the same price as a standing pilot unit. The IPI does not run a pilot all summer so it saves gas. The IPI has more advanced control systems available and takes full advantage of them. We don't even offer standing pilot units unless either that's all the unit is made in, or the customer requests one.

  4. #4
    Join Date
    Dec 2006
    Portland, OR
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    Late to the party. Our shop sells almost exclusively IPI systems from mfg's that offer them. As far as I know, H&G doesn't offer inserts in IPI. I'm a fan of the system, even if it does give up some of the simplicity that makes standing pilot so straight-forward to troubleshoot.

    One problem we run into every year around this time is spiders in orifices. I swear I get two or three calls every day it seems. I know spiders can get into main orifices on standing pilot, but I think we probably see 4-to-1 more spiders in IPI units. I see quite a few nests blocking primary air passages in pilot hoods, also. I've heard guys recommend spraying pesticide on the siding around the termination, not sure what results to expect with that.

    Any other thoughts on spiders?

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