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Timer On Oil Firec Indirect Hot Water Tank?

Post in 'DIY and General non-hearth advice' started by velvetfoot, Oct 1, 2011.

  1. velvetfoot

    velvetfoot Minister of Fire

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    I just got done reading most all the threads on domestic hot water-a fine Saturday morning activity!

    My current 7 year old setup is an indirect tank (BoilerMate) operated as a separate zone of an oil-fired Burnham boiler.
    I'm somewhat unclear how much savings a heat pump or resistance electric heater would provide, esp. with the additonal hassle of wiring it up.

    I've gotten a timer to turn on the heater aquastat maybe a couple of times a day, maybe locating the timer somewhere convenient in case one needed hot water out of the usual time slot.

    I recall reading a thread on this but haven't been able to find it yet.

    I wonder how living with this would be. Like, how long before getting hot water when switch on out of time slot?
    Or, does it really save that much? I do hear it go on periodically during the day, but haven't quantified it as others have.

    I guess I could insulate the tank more, and maybe jack it up and replace the concrete block underneath with and insulating frame, as another poster has done.

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  2. woodgeek

    woodgeek Minister of Fire

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    two things...

    1) if the indirect tank is well insulated, how does having a timer help with standby loss? Does the tank 'go cold' in a few hours? If so, insulate it better and skip the timer. If the timer is on the boiler it makes more sense, but do you really want to cold cycle your boiler that much?

    2) Assuming electric is $0.15/kWh, then a resistance water heater costs as much per delivered BTU as ~$5/gal oil. The one piece HP water heaters have a COP of ~3, so they can heat water as cheaply as $1.67/gal oil. Of course, the HP heater is sucking heat out of your conditioned space in the winter, but your oil boiler has standby losses in the summer (if it is a conventional warm start).

    In my case, my oil standby in the summer is about equal to the amount I burn to heat water in a year, doubling the oil cost. In this case, if oil is >$3/gal (yup) it is effectively more expensive than a conventional electric tank. A HP tank would cost only ~1/3rd as much (ignoring the heat suck)! I am planning on getting myself one soon.
  3. velvetfoot

    velvetfoot Minister of Fire

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    The boiler goes cold if there is no demand. I hear it go on at times during the day in the summer, so I guess the tank could use some insulation. I thought I'd turn on the hot water, say, a few hours in the morning and a few days in the evening with manual overide available.

    While the HP heater has appeal for the dehumidification, cooling the basement might not be that great.
  4. velvetfoot

    velvetfoot Minister of Fire

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  5. Don2222

    Don2222 Minister of Fire

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    Salem NH
    Hello

    Would it be much more efficient to just add another Indirect Hot Water Tank or any type of storage tank in series with the Indirect Tank? This way the cold water coming into the house would warm up to room temperature before going into the existing Indirect for heating.

    Then later on a solar panel and pump or heat pump could be added to the new incoming tank!

    Any comments on this?
  6. woodgeek

    woodgeek Minister of Fire

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    I'm no expert but my understanding is that there is a big difference between the (most common) cast iron sectional boilers and the ($$) welded boilers in terms of tolerance to deep thermal cycling. The sectional boilers are 'famous' for developing leaks when you let them go to ambient temp, and they also are supposed to have enhanced corrosion, higher sooting, shorter life, etc when they run below ~140F. Simply not designed for that. If you have a fancy welded boiler (designed for 'cold start' and 'condensing' operation for high eff) then you are good to go, but in that case your aquastat would already be letting the boiler go cold. In a sectional, you might save a couple hundred bucks a year, and takes several years off the life of your boiler to balance it out.

    If you haven't already, you can set your aquastat to a much reduced temp 24/7 in the summer (120F?, less?) and achieve much the same savings (it will run higher when it has to fill the indirect tank, and then drop back down), and it would prob be easier on the boiler. The elevated temp will keep the joints closed and the whole works dry.
  7. WES999

    WES999 Minister of Fire

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    http://www.leaningpinesoftware.com/hot_water_heater_vacation.shtml
    http://energyexperts.org/EnergySolutionsDatabase/ResourceDetail.aspx?id=4034

    Here are a couple of interesting links dealing with standby loss in hot water tanks.

    They are talking about electric water heaters but I think there are some some similarities with oil fired.
    The conclusion is that a timer would only provide minimal savings.

    I think the point is a timer can only reduce cost due to the standby loss, it may be better just to insulate the thank really well.

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