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  • water heater heat loss

    today (saturday) i repaired a badly leaking water service that i shut off on thursday afternoon. in the process of shutting down the service on thursday, i turned off the circ pump to the 50 gallon gas heater and also turned the gas valve to pilot position.

    advance 49 hours later to today. (thursday 11:30 am- sat. 12:30 pm) i fixed the service and went to turn on the heater. i go to turn the gas from pilot to on, and was expecting the heater to come on. the valve was set at 130 degrees. nothing, i thought i blew out the pilot. so i raise the temperature up and the main burner comes on

    then i turn it down to 125 degrees and the burner goes off

    in 49 hours, the heater only lost approx. 5 degrees with the pilot on.

    amazed me and i thought that all this tankless talk was about saving gas on heat loss


    example #2 to come after all the doubters post.

    rick.
    phoebe it is

  • #2
    Re: water heater heat loss

    I would doubt this story but I had a very similar experience just the other day. 50 gal gas water heater off for 12 hours, I did a repair ( 10 mil tape does not equal a sleeve through concrete) turned water heater back on and it was up to temp within minutes. I wonder how long it takes 120 degree water in an average tank to drop 20 or 30 degrees.

    Comment


    • #3
      Re: water heater heat loss

      That would be an interesting spec for manufacturers to publish...BTU loss per hour at a room temp of 68°F with zero flow. Would give you a good measure of the efficiency of the WH.

      They must have this number already as part of design development. There must be some break over point where more efficiency/insulation does not correspond with what you can sell the WH for. I don't recall seeing it in any literature normally published with a WH.

      I found this list of docuemnts about water heaters on the EnergyStar website:

      http://www.energystar.gov/index.cfm?....water_heaters

      Haven't looked through it all yet. From what I read water heaters don't currently fall under the Energy Star program., seems strange since WHs account for what like 25% of energy use in the home.
      "Water heating represents between thirteen and seventeen percent of residential energy consumption, making it the third largest energy end use in homes, behind HVAC and kitchen appliances. Water heating is the only major residential energy end use that the ENERGY STAR program does not address. To deal with this issue, the U.S. Department of Energy is in the process of establishing an ENERGY STAR residential water heater program."
      Last edited by Bob D.; 08-24-2008, 10:05 AM. Reason: added link
      ---------------
      Light is faster than sound. That's why some people seem really bright until you hear them speak.
      ---------------
      “If I had my life to live over again, I'd be a plumber.” - Albert Einstein
      ---------
      "Its a table saw.... Do you know where your fingers are?"
      ---------
      sigpic http://www.helmetstohardhats.com/

      Comment


      • #4
        Re: water heater heat loss

        I'm not doubting you Rick. I just thought you posted a question and I wanted to see what you didn't know.
        Anyone can tear a man down, few can build one up.

        Comment


        • #5
          Re: water heater heat loss

          While I don't think Rick experiment was very scientific but it has some merit. A foam insulated tank with thermotrap nipples will hold the water hot for several days.

          If the pilot is lit, I believe it can produce 90 + degree water indefinitely. I have accidently left water heater valves in the 'pilot' position and the customer not notice the lack of hot water for weeks. This would only happen during the summer months when the incoming water is still quite warm.

          You can increase your standby heat loss with a fiberglass blanket but those things seem to cause more harm than good. They interfere with the fresh air to burner. Cause the enameled steel jacket to rust up from condensation. Not to mention the smoke/fire hazard. They distroy electric heater components. with condensation.

          With a $30 price tag I doubt you can recoup that cost through standyby heat loss over the lifetime of an average heater.

          Comment


          • #6
            Re: water heater heat loss

            Rick, I have certainly experienced pretty much the same results as you noted.

            One thing think it does point out is why a conventional pilot gas tank never gets above about 60 energy factor....that pilot flame is using up some energy!

            Comment


            • #7
              Re: water heater heat floss

              This is incredable!,and hard to believe RICK!!! We all saw the the North Easter that dumped
              2 ft. of fresh snow on LA!! temps plumeted to 20 degrees below,and with the cold air coming off lake superior, wind chill was 40 below!!!!! Hope National Guard finds that old lady!
              Back to You, NH Master
              I can build anything You want , if you draw a picture of it , on the back of a big enough check .

              Comment


              • #8
                Re: water heater heat loss

                Most of the heat lose on a conventional gas water heater doesn't occur through the jacket. The flue, a classic two edged sword, is the main culprit.

                Comment


                • #9
                  Re: water heater heat loss

                  Originally posted by lovetheUSA View Post
                  Rick, I have certainly experienced pretty much the same results as you noted.

                  One thing think it does point out is why a conventional pilot gas tank never gets above about 60 energy factor....that pilot flame is using up some energy!
                  I think the reason for the lower energy factor is that the flame is not in "direct contact" with water making for poor energy transferance in scientific terms. And you also lose the flue heat energy for safe venting. So while the potential energy available is not used very efficiently it does not mean that in the overall scheme a LP/Nat. heater is not efficient in comparison to other types. Right? Wrong?

                  J.C.

                  Comment


                  • #10
                    Re: water heater heat loss

                    I have mentioned this repeatedly, heat loss has almost nothing to do with tankless's efficiency.

                    My state (and I think most) requires a min stdby heat loss of no more than 15 BTU per square foot of surface area of the tank.

                    That comes to pennies over a month on the avg 40 or 50 gal tank.

                    The savings on tankless is the operating AFUE.
                    They run at 84+% AFUE as opposed to a standard tank types 60%.

                    You save roughly 1/3rd off the water heating bill.

                    A family that uses $80 a month will make the extra money for installation over a tank back in as little 5 years....replacing it will be much less money after that.

                    A person that uses $15 a month won't.

                    I had one customer, a doctor, that used maybe $20 a month between her and her significant other, she was adamant on tankless once she weighed it out because they both like using the jacuzzi and both like long showers...led to alot of aggravation between them on who gets to bath & when and when it was safe to run the dishwasher.

                    As for electric tankless's, forget them, they're useless...VERY few applications that make them worthwhile.
                    Last edited by DuckButter; 08-24-2008, 01:05 PM.

                    Comment


                    • #11
                      Re: water heater heat loss

                      Originally posted by DuckButter View Post
                      I have mentioned this repeatedly, heat loss has almost nothing to do with tankless's efficiency.

                      My state (and I think most) requires a min stdby heat loss of no more than 15 BTU per square foot of surface area of the tank.

                      That comes to pennies over a month on the avg 40 or 50 gal tank.

                      The savings on tankless is the operating AFUE.
                      They run at 84+% AFUE as opposed to a standard tank types 60%.

                      You save roughly 1/3rd off the water heating bill.

                      A family that uses $80 a month will make the extra money for installation over a tank back in as little 5 years....replacing it will be much less money after that.

                      A person that uses $15 a month won't.

                      I had one customer, a doctor, that used maybe $20 a month between her and her significant other, she was adamant on tankless once she weighed it out because they both like using the jacuzzi and both like long showers...led to alot of aggravation between them on who gets to bath & when and when it was safe to run the dishwasher.

                      As for electric tankless's, forget them, they're useless...VERY few applications that make them worthwhile.
                      Good post. I can't agree totally though with the statement "A family that uses $80 a month will make the extra money for installation over a tank back in as little as 5 years." Each installation is different. Too much of a blanket statement. What if the family of four changes their use behavior and use more hot water because the shower doesn't run out of it now?

                      J.C.

                      Comment


                      • #12
                        Re: water heater heat loss

                        Originally posted by JCsPlumbing View Post
                        Good post. I can't agree totally though with the statement "A family that uses $80 a month will make the extra money for installation over a tank back in as little as 5 years." Each installation is different. Too much of a blanket statement. What if the family of four changes their use behavior and use more hot water because the shower doesn't run out of it now?

                        J.C.
                        We could really, really get into complicated things in that line of thinking, like:
                        What if a new ice age hits the area and incoming water temps drop by an average of 30 degree's?
                        Or what if the kids run away from home and the parents are alone?

                        We cannot predict every little detail, yes, showers might tend to be longer, thats not justification for not getting a tankless if the situation warrants one...just take normal showers fer crying out loud!

                        In fact, I have one customer who sent me copies of his gas useage in the summer, I was surprized he wasn't saving more until he openly stated he and his wife intentionally take longer showers.
                        He defiantly enjoys not having to rush in the morning to save hot water for his wife, she enjoys not having to worry she'll get stuck with shampoo in her hair and cold water.

                        Doing some simple math, at 30% with an $80 water heating bill, you save $23.
                        Multiply by 12 = $276, over five years = $1380.

                        My gas co offers a $300 cash rebate for tankless installs, factor that into the equation.

                        The cost for a PV 50 gal with installation is at least $1200, more in most cases.
                        IF (yes, blanket statement) the Tankless cost $3000 to install, the cost makeup is made in five years.

                        Whats constantly overlooked, is the fact that replacing a tankless the next time around will be substantially less because the 3/4" gas is already there, along with the vent through foundation and water lines in place.

                        Comment


                        • #13
                          Re: water heater heat loss

                          My ss40 will hold it's heat for well over a week.
                          sigpic

                          Comment


                          • #14
                            Re: water heater heat loss

                            I replaced both of my water heaters with tankless a couple of years ago and I'm saving about $40 a month in gas, but probably spending $5 a month in electric to run them ( never checked the wattage). A 25 degree morning is considered " real cold" around here and last I checked, I'm paying about 80 cents a therm. I imagine that's about as bad of a payback that a guy could get, especially if I had paid retail for the install.

                            I sure like the never ending hot water though!
                            spodelee

                            Until lions have their own storytellers, stories of the hunt shall always glorify the hunter

                            Comment


                            • #15
                              Re: water heater heat loss

                              Originally posted by NHMaster3015 View Post
                              My ss40 will hold it's heat for well over a week.
                              You meant 45.

                              I did one "experiment" with a SS and it held perfectly for well over 12 hours..I'll take your word on days.

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