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  1. #1
    What is your opinion of the on demand hot water heaters? Are they worth the extra expense. I am trying to decide if I should do that or go with an indirect tank.

    FYI I am putting in a new boiler now too.

    Thanks

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428

    Combination

    Originally posted by pbrousseau
    What is your opinion of the on demand hot water heaters? Are they worth the extra expense. I am trying to decide if I should do that or go with an indirect tank.

    FYI I am putting in a new boiler now too.
    You could use the new boiler as hot water pre-heater to reduce the size(s) of the
    (gas or electrical ?) ON_Demand hot water unit(s).

    You could determine whether 70' or 100'F
    would be an appropriate H.W. pre-heat temperature depending on Your needs/time-of-year.

    If the hot water tank is within the residence,
    then a higher pre-heat temperature in the winter
    would not be a problem.

    http://www.sets-systems.com/product.asp?spec=145#145

    http://www.seisco.com/pages/electric...uirements.html

    For example, 9,000 Watts = 240V at 37 Amps
    30'F rise at 2.0 GPM

    Set pre-heat 85'F - 90'F to get 115'F at the service.

    One does not need to seelct the most expsenive

    http://www.houseneeds.com/shop/Heati...istonIndex.htm

    [Edited by dan sw fl on 11-20-2005 at 11:59 AM]
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Theon demand hot water heaters come with a big price to start, then just keep on taking when it comes to your electric bill.

    They are great for a stand alone sink, but the water going through the heater is real slow so it can heat up.

    I have been down this road myself, in my opinion don't waste your time and money.


  4. #4
    Join Date
    Jul 2004
    Location
    Fort Lauderdale, FL
    Posts
    456
    Buderus makes a wall hunf boiler that does on demand water heating also. I have installed several of these units and I have to say I am VERY impressed
    How much is it an hour?

  5. #5
    Join Date
    Mar 2005
    Location
    NC
    Posts
    230
    We have ran gas lines to the Reniaa (sp?) on demand water heaters. They seem to work pretty good. They may be a bit of a gas hog, but they do get the job done.
    If you can't do it right.....Don't do it!!

  6. #6
    Join Date
    Feb 2003
    Posts
    1,996
    Put the extra money into the best effcient boiler you can get and add the indirect. Better to have the boiler run year-round. Indirect handles a dump load better. If you're putting in a gas boiler, just get a condensing/modulating one so you save on the heating side also. The electric on demand WH require too much power and have low flow rates. I'd only use them in to feed small demand areas like a small kitchen.

    [Edited by johnsp on 11-20-2005 at 10:01 AM]

  7. #7
    Join Date
    Apr 2002
    Posts
    11,808
    I would recommend an indirect water heater over a tankless coil in a boiler.

    The electric instantaneous heaters have their use, and can be thermostatically controlled. They will basically use just as much power as needed with no stand by losses. They require heavy duty wiring and on paper they add quite a demand on to a residential electrical service. If you used a storage tank with them, you have the standby losses-defeats the purpose of having an instantaneous - you have the stand by loss and the tank takes up space-- might as well have an electric tank with big elements.

    I have never worked with the wall mounted on demand gas ones.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  8. #8
    Sorry, I guess I should have included more details in my initial post.

    I currently have a tankless coil for my DHW. I also have finally decided to stick with oil for my new boiler. We had condidered switching to propane and getting a condensing unit as suggested but that was just not cost effective. We are still considering using a propane fired on demand DHW system because they "seem" to be a good product and we also like the idea of a gas cooking range and dryer in the future.

    Does this sound crazy, to have a duel fuel system like that? Is it really worth it to have an On demand system for residentil hot water use? So far it sounds like most of you don't recommend it to provide hot water.

    Thanks


  9. #9
    Join Date
    Feb 2003
    Posts
    1,996
    Nothing heats water faster then oil. Take the extra cash you'd spend on the instant water heater and put it towards a high end 87% efficent 3 pass boiler with an indirect. Better for your hot water, boiler and your oil bill years down the road. Get some boiler controls to do outdoor reset and priority for the indirect so you don't have to oversize the boiler. Best investment you'll ever make.

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