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Thread: more efficient water heaters?

  1. #1

    Default more efficient water heaters?

    hello

    basicly, are the newer hwh's more efficient than older models ?

    i am replacing my 14y/o aosmith 40g with a new richmond 40g.

    just wondering.

    thanx
    Last edited by Terry; 05-03-2010 at 11:30 AM.

  2. #2
    Plumber jay_wat's Avatar
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    yes,,newer models are much more efficient then the older models,,
    here is another brand to think about,if they sell in your area,and they also have a great accessory packages that make the units even more energy efficient

    http://www.bradfordwhite.com/

  3. #3

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    thanx. thats what i thought.

    now. is ENERGY STAR worth while, or a gimic ?

  4. #4
    In the trades Dana's Avatar
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    An apples to apples effiiciency comparison of one tank to another is it's efficiency factor or "EF number". Energy Star units have to meet a higher minimum spec than the absolute minimum allowed by regulation to be sold, so yes, they're more efficient than those that don't meet the spec, but by how much is a function of how well it tested in an EF test compared to the non Energy Star model, and the volume of water you actually use.

    The EF test is a measure of combined combustion-efficiency (if it's a fossil-burner, rather than electric) and standby loss issues when using ~64 gallons/day. If you use more than that your as-used efficiency goes up, since your standby losses drop (and conversely.) In general the smaller the tank, the higher the EF due to the smaller amount of surface area, but with electric tanks that can be overcome by more insulation. With gas-fired tanks added insulation does some good, but the center-flue heat exchanger losses and losses from uninsulated clearances around the burner limit the effect. Standby losses can be signficantly reduced with any tank by insulating all of the near tank plumbing (including the cold water feed and the pressure/temperature valve plumbing.) The 3/4" -wall closed cell foam pipe insulation available at some plumbing supply houses (and online) is usually a cost-effective upgrade than the 3/8"-walled stuff available at box stores.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Because of the r^2 factor in the volume, the volume goes up faster than the surface area, so the surface area say to go from a 40-50 gallon tank is not 125% increase (like it is with the volume), it's closer to a 114% increase in surface area. The bigger thing is the insulation and the burner efficiency, not the standby losses (which still could be large).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    Master Plumber Redwood's Avatar
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    Fabricator,
    Are you talking about gas or, electric?
    Also where are you located?

  7. #7

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    thank you for the in depth replies.

    i am suburban chicago. the unit is natural gas. it is located in the utility room, basicly next to the furnace. it never gets below 70deg, in the winter it can get into the 80's, in this small room.
    wife and i are the only users. and a new dish washer. hot water is used at various times throughout the daytime.

    right now, the room is 74deg. the hwh is 81deg on the outside. water temp is set at 120deg. and i just got out of the shower.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    The warmer that room is, the lower your standby losses. So, I'd consider the larger WH in case you have some guests over some time and need multiple, back-to-back showers. The difference in costs shouldn't be much. One thing to be careful of, though, is proper air for combustion in a small room...the door needs fairly large area of louvers, or some other means of getting combustion air....when both the furnace and WH are on, there's a lot of air going up the flue. This is where a closed combustion system has its advantages.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #9
    In the trades Dana's Avatar
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    Since the thing is inside of conditioned space, in Chicago the standby losses from the jacket insulation are only "real" losses 3-4 months out of the year. The rest of the year those losses are supporting the heating load of the house.

    OTOH, if it's a atmospheric drafted unit a good portion of the total standby losses are going straight up the flue, convecting heat out through the center-flue heat exchanger to be vacuumed out at the draft hood. Even worse, the open flue is also sucking conditioned air out 24/365, driving infiltration of outdoor air inward whether the thing is firing or not. From a water heating efficiency perspective you can guage it by the relative EF numbers, but the whole-house picture is more complicated. Going with an electronic-ignition forced-draft model has true whole-house fuel & AC electricity savings, factors well beyond what is measured in an EF test, and which will vary a lot from one house to another. A sealed-combusion/direct vented version is even one better, since it draws it's combustion air from the great outdoors rather that using conditioned space air, but direct-vent tank HW heaters aren't too common. (Many tankless versions get combustion air from the outdoors, or can be converted to do so.)

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