Hot water issues

Discussion in 'Boiler Forum' started by spta97, Feb 21, 2010.

  1. spta97

    spta97 New Member

    Messages:
    68
    Location:
    New York
    Hey everyone,

    I have a Weil-McLain oil furnace that provides heat (hot water through radiators) and hot water. I do not have a separate hot water tank (there is a small tank on top of it), nor do I really have the room for one. When using one device (say a sink) the volume of hot water is sufficent, however when another device is turned on there is a drop in the hot water volume.

    The tempurature is fine, but because of the defficency in volume you cannot say take a shower and run the washing machine at the same time.

    The boiler is about 20 years old or so and I had one of those "sonic" cleanings done (which helped a bit) but eventually I want to install a new shower down stairs and would like to be able to have both of them running at the same time.

    I had considered upgrading to gas but in order to bring the line to my house would have cost me $31,000 out of pocket :eek: so that's not an option. My only other options are to get a new oil furnace or perhaps look at propane.

    I just wanted to get some thoughts on what I could do to get sufficent hot water to multiple devices at the same time. I was told by my oil service company that my burner is at about 80% efficency.

    Thanks..
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    The type of WH you have are typically not spec'ed to produce much volume - to maintain the temperature rise and provide a reasonably hot supply of water, they ususally have a flow restrictor in them so that the water doesn't move too fast. Forcing it to move slower through the heat exchanger means that it can absorb enough heat to be useful. Think your hand through a candle flame...do it fast, and you don't notice, do it slowly, and you'd burn yourself. Same idea with producing the hot water. the only way you'll get more volume is to store up some hot in a large tank, or buy a different setup to produce more hot 'instantly'. Most of those 'tankless' are designed for NG, not oil. So, find room for an indirect WH tank, or live with what you've got. An indirect WH is functionally installed as a separate zone off of the boiler. You can place it away from the boiler, if that would help, but running the new lines to and from it might be a problem and additional expense. Since there's no burner, the indirect WH could be placed anywhere since there's no flue...as long as you can get the boiler zone heat to it, and can connect to the hot and cold lines to feed the rest of the house.
  3. spta97

    spta97 New Member

    Messages:
    68
    Location:
    New York
    Jim,

    Thanks - that's great advice. Are there any brands you would sugguest? Also, how do you size water heaters? Is it by the amount of devices you want on at one time?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    I've got a SuperStor Ultra. Measure the volume used by each thing you might want to run simultaneously. An indirect can often be smaller than a gas fired or electric heater since you can use the entire heat output of the boiler to heat the water, which is usually a lot bigger than the burner or heating elements of a stand-alone unit. To do this, an indirect is often run as a 'priority zone' (when it calls for heat, it momentarily turns off the other zones to concentrate the heat in keeping the WH output hot). One thing that is often done is to run the indirect at 140-degrees, then put a tempering valve on the output to keep the system safer. This gives the effect of having a larger WH than running it cooler as it can produce more cooler water as it is mixed.
  5. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    It's not a simple question, but with indirect tanks it's more about how much water you need over a quarter to one hour time period rather than the instantanteous flow. The tank itself gives you x number of minutes at some specified flow and the size of the burner adds Y more to that. With a big burner and moderate flow you can run all day long and never run out, even with a relatively small indirect. If your boiler is on the small side, you need more volume to deliver sufficient "first-hour gallons" for running 2-3 showers and a bunch of other stuff.

    Read the specifications for the thing- if it's input is over 180,000 BTU per hour you won't need much of an indirect to support two standard showers (as long as you don't have two teenagers prone to hour-long showers), 20-30 gallons would be plenty, but if it's under 100,000 BTU/hour you might consider 40+ gallons. If you have dreams of building a master-bath shower with massive side-spray gushers you may need even more to avoid running cold.
  6. spta97

    spta97 New Member

    Messages:
    68
    Location:
    New York
    Jim and Dana - thanks. Even though far from my teen years, I am guilty of the hour long shower at times. With just the shower going I never run out of hot water although I find myself adjusting the tempurature from time to time. In the winter I have my boiler set to 160 high /140 low and that seems to do the trick.

    Ideally I would love to have a master shower but in the event I go this route it would mean an additon to the house and probably a separate zone.

    Is there some sort of online calculator I can use to calculate usage? Like average for washing machine, dishwasher, shower, etc? If installing one of these things is just soldering and electrical I can handle it, but I wonder if this is best left to a pro?
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    If the boiler controller has the internal ability to utilize a priority zone, and can support only firing when there's a demand (and is a low-mass boiler), you could probably figure out a way to let it cool off inbetween uses rather than constantly maintaining a certain temperature to make your hot water. This would save fuel. Lots of ifs. While you could run the indirect as a normal zone rather than a priority zone, it might be simpler, but to minimize the size of the indirect, it is usually made a priority zone to get the full output of the boiler. Some controllers support this natively. There's a fairly inexpensive add-on box that can do it.

    Where I live, all WH must be installed with a tempering valve, which complicates things. This valve is adjustable, and forces the water output to be your setting, regardless if the WH is actually hotter (i.e., it mixes cold with the hot to maintain the set temperature). This is a safety feature, sort of like the anti-scald technology required on a shower. It's normally set at 120-degrees or so, whereas a normal temp for an indirect is 140 or more.

    On your shower, if you ever update it, if you install a thermostatically controlled shower valve, you can set it once, and regardless of the WH temp, until you run out of hot, it will maintain your preferred setting. I really like mine.
  8. jimclemmer

    jimclemmer New Member

    Messages:
    4
    Location:
    lucknow
    Hey
    great information for me bcz i seek here how should i adjust the temperature.

    Thanks

    Regards

    Jimclemmer
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