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Thread: spike in ng usage

  1. #1
    DIY Member trw888's Avatar
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    Default spike in ng usage

    I have a 17-year-old Rheem natural gas heater. According to our gas bill, we suddenly started using significantly more gas in September and October than the previous year. The only thing it could be is the water heater. Then today, I heard it making a quiet but noticeable sound. Imagine two (or more?) metal pieces gently rubbing together. It almost sounds like a wind chime rattling in the wind.

    Could it be done for?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    At 17-years, a WH has been on borrowed time for quite awhile. Not to say that occasionally some don't last longer. Depending on your water quality, it could be trying to heat up the water through a very significant portion of minerals, decreasing the heat transfer efficiency. Might be other reasons, and this sort of thing usually comes on gradually, not rapidly. But, your incoming water temperature may be dropping rapidly as winter approaches, and that will cause it to use more gas. You can get the statistics on temperatures - you might want to compare this year with last. Any teenagers home and taking long showers? Doing more laundry with hot? put in a new soaking tub? You could have a leak...is your house on a slab? Any part of the floor seem warm? Take a look at the water meter and while nobody is using any water, check to see if the meter is moving. You might have a surprise in the water/sewer bill coming (they often go quarterly rather than monthly). If it is moving, shut the supply to the WH off and see if it stops.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member trw888's Avatar
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    Thanks for the response jadnashua.

    I live in the desert southwest and it's still pretty warm here so I doubt it's a drop in water temps. Really there have been no significant changes since last year's gas bills. Nothing that I can image that would cause such a spike. I checked the water meter too. No indication of leaks.

    I suspect it's the mineral content. It's just seems strange that it would happen so suddenly.

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    DIY Senior Member Runs with bison's Avatar
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    As it scales up the flue temperatures should rise (lost efficiency, higher natural gas use.) The noise is likely the sound of collapsing steam bubbles on hotter than normal surfaces in the central chimney.

    I would expect such a death spiral to be very rapid once this begins, but have never had a gas water heater die on me yet.

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by trw888 View Post
    I have a 17-year-old Rheem natural gas heater.
    2/3rds of NG WHs have died before now, but if you fix it you have a 50-50 chance of making it to 21 yrs.
    Last edited by Thatguy; 11-18-2009 at 06:48 PM.

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    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Thatguy View Post
    2/3rds of NG WH have died before now, but if you fix it you have a 50-50 chance of making it to 21 yrs.
    Not if it is already scaled up, which is what it sounds like is happening. I doubt descaling it successfully is likely and unless it was a DIY job, the money would probably be better spent on installation cost of the replacement. If the natural gas usage is rising rapidly then it probably is a losing proposition to stick with the old one.

    About the only way to know if it has a chance of repair is to open it up. I wouldn't open it until I had a replacement picked out.

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    DIY Member trw888's Avatar
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    Thanks for insights.

    I won't fix the heater; I'll replace it instead. I just wanted to find out if the end is near. Sounds like it is.

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    Extreme DIY Homeowner Scuba_Dave's Avatar
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    Was the meter actually read ??
    My last house they estimated my use & billed me for more then what I used in 6 months
    DIY Handyman (not 4 hire)
    I have enough to do to my own house

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    Plumber Cass's Avatar
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    you need to discern the exact cause ...you are only guessing now that it is the water heater...you could have a gas leak some where... I would love it if people replaced water heaters just because they though it needed to be...it is very unlikely that the gas usage would spike due to inefficencey...look for something else and save your $$$ for when you do need to replace it...

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    Moderator & Master Plumber hj's Avatar
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    Default noise

    1. Check your water meter to see if it is running without any water being used.
    2. Check your water bill to see if it has been increasing.
    3. Turn off the water supply to the water heater, then open a hot water faucet to make sure there is no flow. Then see if the noise goes away.
    4. If it does, contact your homeowner's insurance company and tell them you have an underfloor leak and see what your coverage is.
    5. Call a leak locator company, not a plumbing company that does leak locating to find where the leak is.
    6. Call a plumber to access and fix the leak.
    7. Put everything back together the way it was originally.
    8. DO NOT replace the water heater, yet. It is probably still good, and if you replace it you might still have the problem.
    9. Water heaters DO NOT burn gas unless they are heating water, and they ONLY heat water when the hot water is going somewhere.

  11. #11
    DIY Member trw888's Avatar
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    Ah geez, a gas leak. Only the most obvious explanation never occurred to me. I haven't noticed any rotten egg smells, but I know the leak is smell there might not be much of a smell.

    There's no indication of a leak either on the water bill or the meter. I think it's safe to cross that one off the list.

    Here's another question I forgot to ask. Over the last couple of months the heater has developed three small holes on the outside of the tank. There all on the same side in the same area near the top. The largest is a little smaller than a quarter, the other two are about the size of a nickel. They have jagged edges that are blackish/rust colored on the inside. I can see the foam insulation through the largest hole.

    What would cause this?

    Thanks again for all the help.

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    The outer jacket is to just hold it together and have a place to install the insulation without it hanging in the breeze. An internal leak is likely, otherwise, the shell wouldn't be rusted. Probably time to replace.

    If there isn't any water flow (leaks), the gas usage wouldn't spike, as was indicated, usage might go up a little because of the added insulation of the mineral deposits, but it shouldn't spike. IF it went up, it would be gradual.

    Last question, did you check actual gas usage, or just the price? The price could have changed radically, and you're looking at dollars verses volume of gas used.

    While you are not using any gas appliances (stove, heat, WH, dryer, etc.) is the gas meter dial moving? Unless you have a standing pilot (and you can turn those off), the meter reading should not move, just like the water meter shouldn't. If everything is off, and the meter's moving...call the gas company! Quick!, and better do it from outside, not inside.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member Runs with bison's Avatar
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    There have been a couple of folks claiming natural gas use wouldn't spike when the tank is near end of life (as in a scaled/sedimented condition.) I would like to know your basis. Because when you scale up a heater, the wall temperature will rise as will the temperature of the exhaust gases. The only way it wouldn't is if the burner rate automatically cut back to control the outlet gas temperature. The burner controls on standard tanks don't appear to be that intelligent. If they continue to run at the same gas rate, the exhaust temp will rise, because heat will be transferred to the water at a fraction of its normal rate. The combustion heat has to go somewhere.

    The impact on efficiency would be negligible for years, but when you do start to reach a critical point it should snowball just like this.

    For more on the subject see:
    http://www.hotwater.com/lit/training/4800r9.pdf
    http://www.inspectapedia.com/plumbin...ter_Noises.htm

  14. #14
    DIY Member trw888's Avatar
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    I checked the gas meter with everything off and it showed absolutely no movement. Whew.

    I going by gas usage not the cost. However, after I checked the meter, I double checked the bills and realize I misread them.

    We went from 9 therms in Oct. 08 to 14 therms in Oct. 09 and from 11 therms in Nov. 08 to 18 therms in Nov. 09.

    So, it's not the any where near the jump I thought initially.

    While our usage patterns haven't changed at all in the last year, maybe I don't have that much to worry about after all.

  15. #15
    Moderator & Master Plumber hj's Avatar
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    Default heater

    Most of the heating of the water takes place in the center flue and that does not "deteriorate" to any great exent over the life of the heater.

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