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Dose LPG age matter?

lostLPG Member Posts: 3
edited January 2023 in Gas Heating
I have a propane Weil-McLain hot water boiler. It is rated under 50k, 8 years old, serviced yearly in July, and the rooms have aluminum wall hung radiators. House is 1,300 sq' ranch with a full unfinished basement. We do have a 2.5 ton HVAC system, but do not use it to heat once it gets below 40*f outside.

During the last cold snap lasted around 93 hours where we had -10 nights and 25's days. The boiler was not able to keep up after the second night and we were fine once we started using our gas logs.

I had the system looked at today and was told it was due to old LPG and that it breaks down losing it's BTU's over time. The technician kid said the propane smell was off. We have a 1,950 gallon underground tank and use around 1,200 gallons a year getting it filled in the summer. The flue gas analysis test was about the same as it has been for the last 3 years.

My understanding is that the mercaptan that is added to the LPG changes smell as it gets old, but nothing in the propane is fine to use.

I think the issue was more on the side that the concrete in the walls ended up getting cold soaked and it was not in the plan when sizing the system.

Dose old LPG loose btu's as it gets old?


  • Tim McElwain
    Tim McElwain Member Posts: 4,629
    edited January 2023
    Yes it may get what is called odorant fade. Have a legit propane company test it to be sure. It will typically still be able to operate efficiently unless it has accumulated a lot of moisture in the tank.
  • Jamie Hall
    Jamie Hall Member Posts: 23,656
    No. As you note, the odourant -- mercaptan -- does tend to dissipate over time. However, LPG is not, in fact, just propane. Varying amounts of butane are also mixed in depending on the expected temperatures Butane tends go be added when storage temperatures are higher, as its boiling point is higher and thus the vapour pressure is lower. This keeps the pressure in the storage tank in a reasonable range.

    The problem, obviously, is that if your LPG is a more summer oriented mix, it won't vapourize as well in very cold weather and you may end up with low gas pressure at your burners. Maybe your regulator can cope -- and maybe not.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,486
    News to me that LP loses btu content.
    With that size underground tank and a 50 K load, it should vaporize without a problem.

    Sure is tough to get that smell out of old, empty tanks, it stays smelly for months.

    I’ve flushed a number of old LP tanks to use them for buffer tanks
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • lostLPG
    lostLPG Member Posts: 3
    @Tim McElwain Thank you I did not know they also tested propane. I will make some calls in the morning.

    @Jamie Hall It is an underground tank so the tank temp should never get too cold, but yes the primary and secondary regulators were in the cold.
    I know propane has 10% other in it and butane can be a pain in the butt.
  • lostLPG
    lostLPG Member Posts: 3
    I ended up emailing the shop owner and told him I was unhappy with the kid they sent out. He ended up stopping by and looked at everything and we had a long talk. The kid that came out is still very green. He thinks I ran short on BTU's as the we were well below the design temp and the kid needs a good talking to.