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Propane overdose

Osborn Member Posts: 31
I have a new vacation house in upstate NY that has radiant heat run a by a 130K btu tagaki condensing tankless hot water heater supplied by 2 100 gallon propane tanks. It's an old 2000sq/ft house decently insulated. This November I had guests in the home for 15 days and otherwise kept the heat (I control the heater with wi-fi thermostats) at 50 degrees. Yes, during that month I apparently burned through nearly 160-180 gallons of propane! Does this figure make sense? It seems like a crazy amount! Comments?


  • Zman
    Zman Member Posts: 7,433
    That does seem pretty high. What were the outdoor temps like?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,782
    Hello @Osborn , Others will give you intelligent answers, but in the meantime, I'll ramble :D First thing is to round up some more data so less guessing is needed. Ideally, a meter on the gas line would allow you to clock the Takagi and really see what its' gas consumption rate is. From there you could calculate how many hours it would have needed to run to use that much gas. Did your guests keep it at 90*? If you can get your hands on an IR camera like the Flir One, you could have a look at the house and see if there are any big heat leaking holes in it. Do you have heat loss numbers for the house? That would have been needed to size the heating system. Also, if the radiant system is in a slab, it will take energy to heat it up first time, but once heated, it should require much less energy to maintain temp. Or maybe there is a gas leak and propane leaks can be very bad! Lastly, is there any way someone could have stolen gas from the tanks? Crazy brainstorming, I know. :p

    Yours, Larry
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,932
    edited December 2019
    another rambling thought is the fact that you had the temperature well above the normal 50° for half the month. If your propane supplier is counting degree day usage for automatic delivery, your abnormal use will cause you to run out of fuel before the regularly scheduled delivery. (unless this is normal to use the cabin for 15 days a month) How much fuel was in the tank when your guests arrived. You may have used some before they arrived. What was the delivery date before the large amount of usage? If you don't use automatic delivery for propane delivery then as the famous american editorial commentator Miss Emily Litella said ......Nevermind
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • Jamie Hall
    Jamie Hall Member Posts: 20,434
    Bottom line quite possible -- but check degree days for usage comparison.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ratio
    ratio Member Posts: 3,332
    Does the Takagi heat the domestic water as well?
  • Icarus
    Icarus Member Posts: 143
    There are ~90,000 btus in a gallon of propane. You can do a quick calc guesstimating the run time of the Takagi. The 130k btu of the takagi running full out will use ~1.4 gph. 15 days, running 1/4 time = 1.4X6X15=126 gallons. Given the info you have provided, it certainly seems possible. Also, with out knowing exactly how much was in the tank before, and after (just guessing from the suppliers fill doesn’t give you an accurate count on one filling) it certainly sounds about in the ball park.

  • Osborn
    Osborn Member Posts: 31
    Thanks everyone. This is a great resource. I know its a big no no on this site but I designed and built the system myself over several years and just didn't expect this kind of use. Its a very very old house -- 1830- and we've done a lot, but still original doors, leaks around the sils, uninsulated crawlspace under 1/3 or the house etc...

    I will make sure there are no leaks and then keep on with what seems like lifetime job of airsealing and insulating the place.

    Best and thanks all.
  • Zman
    Zman Member Posts: 7,433
    Was the boiler converted to propane? Has a combustion analysis been performed?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    EBEBRATT-Ed Member Posts: 13,112
    Make sure there are no leaks in the gas piping
  • mattmia2
    mattmia2 Member Posts: 7,156
    90,000 btu/gal * 180 gal = 16,200,000 btu consumed
    16,200,000 / (30 days/month * 24 hours /day) = 22,500 btu/hr

    How does that compare to your heat loss calculations from when you designed the system? That seems like a reasonable loss for that structure, especially if you had the same unusually cold November that we had.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,542
    Also a tankless water heater will not condense much at heating temps. So your efficiency will drop significantly when the place is heated to livable (above 50!) temps.

    You use may go up significantly due to much higher return temps when people are staying there. This is circumvented when you're only heating it to 50 when it's unoccupied. A condensing boiler is made for heating, a condensing tankless water heater is designed to have 50 degree incoming water to condense.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • mattmia2
    mattmia2 Member Posts: 7,156
    I didn't catch that it was a water heater.