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Insulation Blanket on New Water Heater?

Post in 'The Green Room' started by velvetfoot, Sep 18, 2012.

  1. velvetfoot

    velvetfoot Minister of Fire

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    Do people still put insulation blankets on a new water heater?
    I measured a 3*F temperature difference from ambient and the skin of the water heater.
    I'm leaning towards doing it.
    I put a 2" piece of foam under the tank, insulated the lines and put in heat traps.

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  2. woodgeek

    woodgeek Minister of Fire

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    3° works out to be ~10 BTU/sqft.hr. This estimate sounds ok if the foam is thin, say 1" and R-7. IF the area is 50 sqft, that is 500 BTU/h, or 150W, or 3 kWh/day or 1000 kWh/yr. A good blanket would prob knock that in half, saving $50-70/yr. No brainer.

    For a more eff heater with 2+" of foam, the savings would be a lot lower, and it would be harder to get excited about it.
  3. jebatty

    jebatty Minister of Fire

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    IMHO, absolutely "yes" but "no" to the commercial, 1" or so of fiberglass. Electric hwh's have a big advantage because you can insulate under, sides and top. I used 6" of regular house unfaced fiberglass insulation all around, then wrapped alum foil bubble wrap around that, as much for aesthetics as anything else, taped the seams. That plus U-shaped heat traps and insulated hw pipes dropped the electric usage by 50%. Total cost about $50.00, payback in a few months (our electric usage, separate meter, is about 90-100 kwh/mo; was 2x that before the insulation, etc).
  4. velvetfoot

    velvetfoot Minister of Fire

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    Thanks. How did you keep the unfaced stuff in place before the bubble wrap?

    On a side note, the oil flue was leaking water down its sides yesterday, as it does in heavy, wind-driven rainstorms. I had to put a 5 gallon bucket on top of the new water heater. So, I guess I'll be going back on the roof again (not looking forward to that), though the last time I tried to stop the leak it didn't work. Just happens infrequently. But, it's something I have to think about.
  5. jebatty

    jebatty Minister of Fire

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    I used some plastic marker tape without adhesive.
  6. velvetfoot

    velvetfoot Minister of Fire

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    Thanks. I'll have to figure out how to "waterproof" it first, I guess. :)
  7. dougstove

    dougstove Member

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    jebatty: That plus U-shaped heat traps and insulated hw pipes dropped the electric usage by 50%.

    Hi - could you explain the U-shaped heat traps?
    A downward U in the cold water feed?
    cheers, Doug
  8. jebatty

    jebatty Minister of Fire

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    Doug, a U-shaped trap: starting from the risers (applies to both the cold and hot water risers on the hw heater), piping that extends 12-18" vertical upward (a little longer is better than being too short), then a short horizontal span (the width of 2 L's is OK), then a vertical drop 12-18" (or more), then typically piping (vertical/horizontal from that drop to the cold water supply or the hot water feed. The principal is that hot water from the hot water heater will rise through the risers to the top of the inverted U by thermosiphon and then thermosiphoning will stop at the L's at the top of the U due to the vertical drop. I found, even with the supplied internal heat traps on my hot water heater, during periods when hot water was not being used that hot water was rising and flowing in both the cold and hot water lines by thermosiphon into the piping and wasting hot water. The supplied internal heat traps were not very effective in preventing this.

    You easily can check your hot water heater. After a period of no use of hot water, feel the pipes at various distances from the hot water heater. If they are warm, you are losing hot water via thermosiphon and wasting electricity and U traps will prevent this.

    I don't know exactly how much difference this makes, if any, but I insulated the short vertical risers of the U from the hot water heater and I did not insulate the vertical drops.

    Attached Files:

  9. Ehouse

    Ehouse Minister of Fire

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    I'm going to try this! I wonder if a Pex loop would do the same thing?

    Ehouse
  10. woodgeek

    woodgeek Minister of Fire

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    yes it would. In would be better b/c of the reduced thermal conduction in the pipe wall.
  11. Huntindog1

    Huntindog1 Minister of Fire

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    I bought the hot water heater that already the 3" of insulation built in. It was more expensive but it also had a electronic heat control with an energy saver setting on it. I also set my temp to 120 degree's.

    I hope its saving me but I havent checked.
  12. EatenByLimestone

    EatenByLimestone Minister of Fire

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    I threw one on my NG water heater at my old house (now rental). I don't have any proof that I saved a great deal, but the blanket is not something that will wear out so the cost can be spread out for decades, I'm sure it will make up the little I paid for it.

    Matt
  13. Mr A

    Mr A Minister of Fire

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    I have often thought of building an insulated closet for the water heater. I have just replaced my water heater, it has been running without a insulation blanket a few months, I have not noticed a difference in the bill. My WH is located in uninsulated garage area.
  14. jebatty

    jebatty Minister of Fire

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    Is this math correct? In Sept we used 89 kwh electricity for the hot water heater according to our electric bill. Here's the computation:

    89kwh x 3400 btu/kwh = 302,600 btu equivalent
    302,600btu / 30 = 10,087 btu/day

    btu to raise 1 gal water 70 degrees (assumed 55-125 temp rise) = 1 gal = 8.3lbs/gal x 1btu/lb/degree x 70 degrees = 581btu/gal

    10,087btu/day / 581btu/gal = 17.4 gal/day of hot water
    household = 2 persons
    17.4 gal/day of hot water / 2 = 8.7 gal/day per person

    Our household is me and my wife + occasional guest and family visits.

    There are various studies on average US dhw consumption, so the numbers will vary. But Engineering Toolbox shows for homes average per person is 20-35 gal/day. My wife and I are pretty conservative on use of hot water.

    All of this assumes 0 heat loss and 100% efficiency in use of electricity furnished to hot water at the faucet, which of course is not true. But it does provide an interesting look at the amount of hot water we are using.
  15. velvetfoot

    velvetfoot Minister of Fire

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    That would mean 1068 kw-hr/year.
    As a sanity check, my 40 gallon heater had a tag of 4773 kwh/yr, so that would mean you'd be using 1/4 the water of the average household.

    Also, I've seen that the DOE test procedure is based on 63.4 gallons per day.
  16. tlc1976

    tlc1976 New Member

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    I keep wanting to insulate mine but it is under the house so I keep forgetting about it. I visualizing building a simple box around it and then stuffing it with loose insulation. All are things I have or can get for free.

    Then again I am always concerned about robbing so much heat from under the house that the pipes freeze. I had that concern when I quit using the furnace in 2006 but it hasn't been a problem. The only other thing that is left down there to make heat is the water heater.

    I've also thought about during the part of the year when the temps are well above freezing, just turning off the water heater when I am gone most of the day or all weekend. I wonder how many throws a typical breaker can take before wearing out?
  17. Frozen Canuck

    Frozen Canuck Minister of Fire

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    Far fewer than most people imagine they can. Install a switch. Cheaper to replace as well when they wear out. Good idea shutting it off when you are away.
  18. woodgeek

    woodgeek Minister of Fire

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    Most (modern well insulated electric) tanks can hold heat for days. During the hurricane, I had a warm shower 4 days after the lights went out. So, IMO, daily timers or flipping the thing off over a WE are a waste of effort (if you are well insulated).
  19. velvetfoot

    velvetfoot Minister of Fire

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    Since I started the thread, I thought I'd mention that I did indeed wrap it with fiberglass roll insulation and put the shiny bubble stuff over it to make it look a little better.
  20. semipro

    semipro Minister of Fire

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    Its probably been said and I missed it but it helps to insulate between the heater and the concrete slab it may be sitting on.
  21. velvetfoot

    velvetfoot Minister of Fire

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    It was said in the first post:
    "I put a 2" piece of foam under the tank, insulated the lines and put in heat traps. "
  22. tlc1976

    tlc1976 New Member

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    Good info. Now I think about it, mine was installed sitting in the dirt under the house. Besides the ground being a huge heat sink, I am surprised it is not rusted out by now but the tank itself may not be in the dirt. Digging out under it and building an insulated base would be a good idea whenever I replace it, but for now I have a feeling it's better to leave well enough alone. It was well used when I moved in back in 1999. In 2003 I put in new thermostat and reset button devices because they had gone bad and kept tripping. Hasn't tripped since. Back in 1999 when I was single my electric bill was $50-$60 a month and now in the same predicament it is $60-$70 a month. But I have more devices and a kid here sometimes too.
  23. jdp1152

    jdp1152 Minister of Fire

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    I've asked a good many plumbers and builders about water heater wrapping. Most discouraged it as it can mask other issues with the unit. Insulated closets were preferred for producing savings. That's my plan over the holidays.

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