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500 gal Propane tanks/gage accuracy

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I agree with JP re: gauge on the LP tank. Drivers stop filling based on vapor changing to liquid at the spit tube (liquid level). The round % gauge is not a calibrated device and is for approximation only.

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  • T Towne
    T Towne Member Posts: 35
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    500 gal Propane tanks/gage accuracy

    Hello Gents

    I recently converted my heating system over to a Lochinvar Knight boiler. Using heating degree days and the gage on the propane tank I am estimating the useage. To my total suprise I am not seeing any propane savings/HDD. According to the gage, I used 100 gallons(20% of tank) from Oct 26th(date tank was filled to 80%) till Nov 25 (gage showing 60%)with old system and 100 gallons from Nov 26 till now(showing 40% on the gage) on the new system. HDD for both periods are virtually the same.

    The old system was using a Bradford White 50 gal 65000btu water heater as the only heat source. Heat loss at 0F is 39,000btu and house is very tight. Contractor said I needed to add ventialaion as blower door test revealed house at 700 and needs to be at 1400. House is Cape style 1800sf.

    We use propane for the dryer and the oven/range as well (i cant see this useage going up to an affecting degree.

    The only things I think it could be is the accuracy of the gage on the propane tank or perhaps the boiler is running rich. Initial combustion test was in spec. I added a zone with this new system but its small and shouldnt make that much difference as it is only making up heat when the floor can't keep up in the upstairs bedroom. Really upsetting as I was expecting to see 15-20% more effeciency as I was told my Water heater was "very ineffeciant" 80%. Any thoughts on the accuracy of the propane tank gages or other possabilities. Thanks.

    Tom
  • jp_2
    jp_2 Member Posts: 1,935
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    system running?

    what is your supply and return temps?

    any picture of piping? how is it layed out?

    i could easily imagine the guage being maybe 5-10% off.
  • T Towne
    T Towne Member Posts: 35
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    JP & Frank

    Supply & return temps are dependant on ODR but because of warm NY December they are fairly low, i.e. should be condensing at least 3/4 of the time this month. Now, the main heat is the radiant floor and all I did here is run the boiler DHW circut (180 out) to a flat plate HX and from there to the space heating in/out of the water heater, this supplys heat to the floor and DHW. I know (legionella trap) but I set aquastat at 140.

    Must be the Gage on the propane tank along with the minimal extra heat used by the new zone!!!! I'll have the combustion values checked again to be sure they are in line. Just frustrating to not "see" the increased effeciency I was expecting. Thanks for the input.

    Tom
  • lchmb
    lchmb Member Posts: 2,997
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    temperature

    Tom if you filled your tank to 80% while the product was 60 degree's and never used it, and then the product temp dropped to 40 degree's you would see a drop in the percent in the tank. A tank guage is only an estimate, not an exact device. I would wait for your first fill and see what you get for a degree day reading...
  • Bob Harper
    Bob Harper Member Posts: 1,049
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    LP tank gauges

    Agree w/ all previous posts----those gauges are a crude convenience to give a rough idea. Liquid level fluctuates with temps. Even refilling is inexact. Less so than refilling your car. You can install a temp. compensated meter then do the conversion. ~$200.00.
  • Steverino
    Steverino Member Posts: 140
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    Keep in mind that tanks are not filled to the top to allow for proper evaporation of the liquid.. A 1000 gal unit holds about 850 gallons. Your 100 gallons is not 20% of the tank capacity. Ask your dealer how much is actually in the tank at fill.
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