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Time to replace boiler & DHW

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Val4
Val4 Member Posts: 7
in THE MAIN WALL
I have a house with a 1985 BPG HeatMaker HW 90% boiler which supplies heat through 4 zones as well DHW. It is rated 130K BTU. It never ran out of DHW. The house does not have a chimney so it vents through the rim joist. The house is very low cost to heat due to the heavy insulation 2x6 walls, tight construction, triple glass, passive solar & located north of Denver. There is a lot of winter passive solar gain so the heat currently cost about $175/yr  and DHW cost about $400 /yr for the 2800 sq ft. I just did a heat study to find that it has heat loss of 36,000 BTU/h without consideration for the solar gain. The house has an attached shop which is heated to 40 F when the outside reaches the low of -10 plus occasionally heated, for use, but not more than that dT 50 for this there is a 18,000 BTU/h loss. There are four heating zones, each with a thermostat. One zone seldom runs, while one zone runs often. No space heat is ever needed April to mid October, often another month on either end of that time.    

The HeatMaker cast iron tank has started to leak from the bottom. The cost for replacement is too much for a 28 yr old system. So I have begun my search for a replacement heating and DHW system. I am looking for ideas. I must put in a side vent system & must have a solution for DHW as well as space heating. The heat needs for the zones varies widely due to the solar gain. When the sun is shining on days the outside temperature reaches 30, from a nightly low of about 15 there is very little heat needed accept possibly in one of the four zones.

Taking all of this into consideration I am considering a boiler which heats the house as well as the DHW. I believe I would like a system that shuts down when there is no heed for space heat nor DHW. It seem that an outside temperature reset would be good, however I do not know if these systems then heat up to the desired temperature when there is a call for DHW in the indirect fired Water heater. I am not so sure that a 96% system is good because the additional cost would never have a pay back by the fuel savings. Obviously cost is a consideration. For these reasons I am considering an 85 to 90% system such as the Larrs NeoTherm vs the Laars Mini Therm, but not the Mascott II. I am not fixed on this brand, only used it as an example. I need to know the desired total BTU size that would be good as well as the indirect fired water heater tank. I do not want to run out of DHW.

 I am looking for ideas and recommendations. I did contact one contractor who looked at the current system and gave me a bid on 3 systems with the 130 BTU 95% due to the size and type of my current system without any consideration for a heat study. I showed them the door. That is brings me here.

Comments

  • Val4
    Val4 Member Posts: 7
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    systems recomended

    I have now had three systems recommended by different installers.

    1.) Burnham ESC4

    2.) Burnham SCG4

    3.) Weil_McLain GV90+4

    All of these would be used with an indirect water heater,  considering Smart or Weil-McLain.

    I have the natural gas used in the house to heat the house as well as DHW on the old system for the past several years. It stays within 550 to 600 Therms for the year and highest amount used in one month is 125.Due to the solar gain it only heats the house during Late November to mid March when it drops to about 17 to 30 therms per month for the DHW.

    Anyone with input?

     
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited February 2013
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    What Is the

    DHW demand? How many showers and what's in them? One the issues with installing a non condensing or even a combi style boiler is that your going to have to address short cycling with installing a buffer tank.

    There was an error rendering this rich post.

  • Val4
    Val4 Member Posts: 7
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    Showers

    Three showers in house, 4 showers daily all with 2.5 gpm flow. In the past three years  Therms of gas used in summer has only been low 20 , high 30, average 25. The total Therms for the year doing both DHW & Space heating is 550 - 600 therms.
  • Zman
    Zman Member Posts: 7,572
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    Mod/con

    I disagree with you reservations on mod/cons. A single stage boiler sized at 90.000 Btu's is going to short cycle and give you low efficiency.

    I would look at a triangle tube prestige 60 with a 40 gallon smart tank. it will modulate down to 12k btu. The real world efficiency differences are are going to be more like 20-30%. Triangle tube has a training center in Denver and well supported.

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • CMadatMe
    CMadatMe Member Posts: 3,086
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    DHW

    How many of those showers are running at the same time? Indirect is the better play match with a mod/con.

    There was an error rendering this rich post.

  • Val4
    Val4 Member Posts: 7
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    Shower use

    Normally only one shower at a time.
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited February 2013
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    Low heating bills high hot water...

    How about a Rinnai Tankless water heater {should only be $250 a year} and a small sealed gas boiler {direct vent or power vent}? Cost would be low, with your obvious small load you should have plenty of heat, and a tankless wont run out of hot water...



    I vote for a Victory VSPH60 and a rinnai ru98...

    or maybe a vsph90 and a smart 40 tank with a priority control... Normally I wont upsize the boiler for a water heater but that is here, it seems you may have colder climate and I can't speak to how to go about adding the load to your system, so better safe than sorry...
  • Gordan
    Gordan Member Posts: 891
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    If it's a standard 2.5 gpm shower...

    A mod-con in the 60000-ish BTU/hr range will be able to provide a continuous shower. That's what I have (with a 26 gallon reverse indirect) and I've yet to run out of hot water with consecutive showers.
  • Val4
    Val4 Member Posts: 7
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    Have considered Combi too

    Current system - Heatmaker is a combi. In the past the only problem with DHW has been the Watts tempering valve which allows the water temperature change to much, requiring one to adjust the temperature more than once while showering. While heating a house zone, the boiler operates up to 200 F, but when only heating DHW it operates at 160 F. These temperate are not adjustable, unless different temperature sensors than spec were installed. Do current combi unit still work like this? How about the Rinnai?
  • Val4
    Val4 Member Posts: 7
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    Operating cost are low

    I just reviewed the gas operating cost for the current system for the past three years. The three year average cost for heating the house has been only $160 per year. The non heating 7 months plus the same amount removed from the heating season cost are $200 per year, and this last number also includes the Dryer and gas grill cost. It seems that the Mod/cond units all cost nearly double for just the boiler over the cost of the lower efficiency units. At a current annual operating cost of $360 / yr, that seems impossible to recover the additional amount spent. Anyone's thoughts?
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