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best replacement boiler

I have a 1956 radiant system in a slab single level home of 1800 sq. ft.. The gas boiler needs to be updated. One installer tells me he wants to put in a Munchkin Contender, the price is good but I am concerned about repairs down the road. I hear it is an entry level model good for about 10 years. The alternatives are a Lochinvar Knight for $$$ more money or a HTP Pioneer Heating Appliance (made by same company as Munchkin) that looks like a small water heater. It is designed as a replacement unit for Eichler homes without the use of a loop system.



Any suggestions on direction or experiences?



Steve

Comments

  • CMadatMe
    CMadatMe Member Posts: 3,086
    The Best Boiler

    Is the boiler installed by the contractor that you feel is the most qualified for the job. Did the contractor do a heat loss? A heat loss should be your first clue as to the contractor you want. From there, ask for references for installs on the same piece of equipment he has installed before.



    Asking for the "best replacement" is very vague. Does the best mean the most expensive? I take each job on its own merit. Budget and application play a big role in choosing equipment. Viessmann Vitodens, Triangle Prestige, the Knight are all great boilers. But like anything else they are only as great as they are installed and set up.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Lawtonco
    Lawtonco Member Posts: 3
    Why

    Why would I need a heat loss if I am replacing a boiler?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    ?

    How would you choose the "best replacement" without one? A heat loss is required to properly size the replacement boiler. How do you know that the existing boiler isn't oversized? Was a heat loss done when that boiler was installed? Last question, how many btu's is the existing boiler?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Lawtonco
    Lawtonco Member Posts: 3
    BTU

    120,000 in, 96,000 out. the replacement was going to be 50,000 in



    Steve
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited December 2010
    The 50 is closer than the 120....

    But I would still recommend a thorough full home analysis. Not just a simple heat loss calc, but full blown blower door test.



    Technically, the limits of a radiant surface you are in contact with (floor) is 85 degrees F, or around 30 btu/sq ft /hr. The 50 would put you at 25 btu/sq ft//hr. And that is the smallest boiler available.



    But the conservation effort is still worthwhile. Many times, your utility will help subsidize the cost of the energy audit.



    If the boiler will also be doing the DHW, then you will need to consider a larger boiler because the 50 ain't gonna cut it. I have one, but it requires a drain waste heat recovery heat exchanger to make it work, and it runs right on the naked edge at that...



    And it absolutely will NOT fill the tub with hot water (The wife is not happy about that. Gotta get that solar DHW system installed soon...) because the drain waste heat recovery exchanger isn't in the picture during a tub filling process :-(



    And as Chris said, you are marrying the installer first. The boiler is just his baggage. Make certain you are comfortable spending the rest of your life and the boilers life with the installation company. That is more important than boiler brand.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Gordan
    Gordan Member Posts: 891
    I gotta ask...

    Mark, if I recall correctly, you've got a reverse indirect hooked up to your small boiler. Have you considered installing a "sidearm" storage tank to extend the BTU storage of the reverse indirect (which ain't big)? You could have the aquastat fire off a circulator instead of firing off the electric heating elements. It would then be relatively easy to convert that to solar DHW later.



    You could also bring the tub back into the picture... if you use that tank as a preheat tank, and circulate through the waste heat exchanger with the help of a differential controller. GFX has something on that on their site, though I'm somewhat dubious.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    My house in Denver...

    has the reverse indirect, and it actually works fantastic. I've NEVER run out of hot water with it. 80 gallon Amtrol. Don't even bother trying to find one in their catalog. They built it special for me as an experiment.



    My home in the mountains is where I just installed the Lochinvar WBN051 with a FPHXer, and the waste heat recovery system, and yes I considered putting the electric water heater in parallel with the load, but don't have room for it and the solar PH storage tank, so SHE will have to live with the shortages until I get 'er done :-)



    Truth be known, she rarely, if ever uses the tub up there. Hard water, high iron content and all. She inadvertently ate some seeds (rye bread) and got a bad case of stomach ache blues (diverticulitus) and decided to take a hot bath and see if that helped. Unfortunately, she didn't get a hot bath. But I got a hot shower of cuss words.... ;-)



    Also, the electric water heater I displaced in the mountains was having an "odor" issue from the bacterial reaction with the magnesium anodes, and she doesn't miss THAT odor....



    But thanks for the thoughts, just the same .



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited December 2010
    My house in Denver...

    FWIW, I didn't double click. Swear on a stack of pump flanges....



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Gordan
    Gordan Member Posts: 891
    I'm wondering whether I'm in for the same...

    A shower of cuss words, that is. Got myself the Turbomax 23 to hook up to the Prestige Solo 60. That gives me some thermal storage, but not much.



    I'm of a somewhat spartan mindset when it comes to energy use and the Solo is already oversized for my heat load, plus I didn't like the piping compromises inherent in the Solo 110 layout, with the internal circ and two supplies. I'm less worried about the showers than about that bathtub. With 26 gallons at 160 F, and cold at 40 F, I should just about be able to make 50 gallons of 105 F water. And supply one continuous shower with a low-flow shower head. What I don't know about, and haven't ever really been able to find out even here, is how the draw temperature varies with time and how "fully" I can "charge" the reverse indirect. If I were to have to extend the thermal mass, would you think it'd be better to do it on the boiler side (piping the buffer in on the supply side of the reverse) or the domestic side (perhaps using it as a preheat tank and recirculating through the reverse's coil)? The advantage of the former would be that it's a simple repipe with no additional controls. Well, maybe I'd wire the aquastats on the two tanks in parallel to the Solo's DHW call terminals. The advantage of the latter would be that I could store at a considerably lower temperature, and minimize standby losses - but there may be a legion of reasons why that's not such a hot idea. Pardon the puns.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Once the systems hits a point of stability...

    and the load is locked into the source, supply temperature will be consistent, and the only thing that will cause the discharge temperature to vary, would be the load.



    If you had to increase volume, I'd rather do it on the DHW side instead of the boiler side. Doing it on the boiler side can lead to a lag in production at times. You could use a simple differential controller to move water between the two tanks, keeping the tank stat separate from the delta T controller.



    As for charging the tank, with the right pump, there will be very little stratification in the tanks during charging. This can change with small draws over time, but when in the charging mode, it should be nearly the same top to bottom.



    When a big draw does occur, there will be a little bit of hysteresis (slop in control) but once everything is stable, out put will be a constant.



    The calcs for filling the tub are straight forward.



    50 gallons times 8.33 times times differential in temperature = load. So in your case, 50 * 8.33 * (105-40) = 27,072 btu's.



    If your holding the tank at 160, and your lowest allowable temp is 105, then the math for that is 160-105*8.33*23 = 10,537 btu's. To this you can add the output capacity of the boiler during draw. 60,000 * .9 = 54,000 btu's/hr.



    54,000 / 60 minutes = 900 btu/minute.



    900/8.33/65 = 1.66 GPM of 105 degree F water.



    So, to fill your tub, you needed 27,000 btus. You got 10,537 out of the R/I, leaving you with a deficit of 16,463 btus'/ 16,463 divided by 900 = 18 minutes to a tub full of 105 degree F water. Your wife is going to have to learn how till fill the tub based on time. The slower the flow, the hotter the water. My wife knows exactly where to set the flow on the tub filler, and does start filling the tub when the 10:00 news comes on, and when the weather starts, she goes and gets into a nice hot tub of water.



    Such is the minor price of energy conservation.



    HTH



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Gordan
    Gordan Member Posts: 891
    Thanks, that is reassuring!

    The math is simple, true. The part that was worrying me was just how many stored BTUs I could expect with a R.I. due to their different construction. Thanks for clearing that up for me!
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