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    wondering if they did not undersize my boiler (12 Posts)

  • debu debu @ 9:18 PM
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    wondering if they did not undersize my boiler

    hi,
    a company replaced my old boiler by a lochinvar solution 75000 btu and now, it seems that if it is really cold, it can not reach the temp. i have about 130 feet of radiator. i set the temp to 65 at night, at 5AM i raise it to 71 and if it is cold outside, at 9 AM it is still not passed 68 in the house (i have three zones, about 2100sqft and the temp is managed the same on the three zones) now the tech tells me i should leave the same temp all the time, because it is a two stage boiler, it would be efficient. why did they install programmable thermostats then? did they put a boiler too small? i think the older one was 90000 btu.
    if anyone has comment/advise or whatever else, anything at this point is welcome.
  • Paul48 Paul48 @ 9:28 PM
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    What

    did they come up with for a heat loss on the home?
  • Jean-David Beyer Jean-David Beyer @ 9:53 PM
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    I do not have all the answers, but you did not provide all the data anyway.

    My house hasĀ  baseboard in the upstairs zone. Much more than normally needed because I wanted to supply water at 135F maximum instead of the more usual 180F. And that would work fine if I did no setback at night, but I do; 1F setback, from 69F most of the time to 68F from about 9PM to 8AM. And the thermostat goes into recovery about an hour before 8AM. Still, it seldom recovers by 10AM.

    But this is not because the boiler is too small: It could put out 70,000 BTU/hour if I set the supply temperature high enough, and the zone needs at most 6500 BTU/hour when it is 14F below design temperature.

    So why does it take so long to recover? Easy: the outdoor reset is set so tight that the boiler delivers just enough to maintain temperature based on the thermostat setting and the outdoor temperature. If I do a setback, it does not supply enough to recover quickly.

    Perhaps your boiler has outdoor reset that is adjusted so its reset curve is as tight as mine. In that case, I suggest you do not setback at all, or that you let your reset curve deliver somewhat hotter water so the system could recover faster. The latter would probably lose you condensing (if you have a mod-con) and use up any savings the setback might have provided. (IMAO, a two stage boiler is use a simple version of a modulating boiler. This could probably be debated by the professions that have more knowledge of this than I may have.)
  • Aaron_in_Maine Aaron_in_Maine @ 10:19 PM
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    Outdoor reset

    Does your new boiler have outdoor reset. If it does it will take a while to recover from that type of setback at night. I would only turn it back no more than 4 degrees. I usually tell customers that outdoor reset is like the rotisserie that they sell on tv just set it and forget it. Let the boiler do the thinking.
  • bill bill @ 4:58 AM
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    wondering if they did not undersize my boiler

    There is a double negative there somewhere.
    Also, we used our ratty rotisserie two nights ago. The chicken was great.
  • heatpro02920 heatpro02920 @ 7:19 AM
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    Im thinking ODR settings..

    Do you have temp gauges on your boiler, check your boiler temp in the morning, Ill bet it is really low. Either set the T-stat to start calling earlier or set the ODR to supply warmer water, how many square feet is the home? Did you have a heat loss done? What is the coldest temp you see outside on the coldest day?

    You could be under sized, But I have installed -75K BTU boilers in 3000sq ft homes, it all depends on your heat loss...
    This post was edited by an admin on February 15, 2013 7:20 AM.
  • Zman Zman @ 12:15 PM
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    Heat loss

    On one hand, your radiators are probably capable of producing an average of 550 btu/foot. That would mean 71,500 for max radiation. Your boiler is producing something in the low 60,000 range.
    The real question is what is the heat loss of the house. How much heat does it loose on your coldest day?
    Without more info, l really doubt is more than 25btu/foot.
    I think your boiler size is most likely appropriate.
    I think you may be falling for the myth of energy savings and short term setbacks.
    Carl
  • Zman Zman @ 12:15 PM
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    Heat loss

    On one hand, your radiators are probably capable of producing an average of 550 btu/foot. That would mean 71,500 for max radiation. Your boiler is producing something in the low 60,000 range.
    The real question is what is the heat loss of the house. How much heat does it loose on your coldest day?
    Without more info, l really doubt is more than 25btu/foot.
    I think your boiler size is most likely appropriate.
    I think you may be falling for the myth of energy savings and short term setbacks.
    Carl
  • JohnNY JohnNY @ 2:33 PM
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    I install Lochinvar Solutions all the time lately.

    The last two we installed needed to have their gas valves adjusted to bring up the gas to the proper manifold pressure. A few days ago, we checked one and the manifold's gas pressure was at 1/2 inch water column while the unit calls for 3.5 inches water column.

    Not cool. We set it up right and the boiler's humming away nicely.

    That customer's complaint was that when we got a few 10-15 degree days recently, the boiler's water temp never got over 160 and the building was "chilly". By raising the gas pressure to its proper setting, we added nearly 50,000 BTUs to the boiler.
    This post was edited by an admin on February 15, 2013 3:36 PM.
  • Chris Chris @ 3:22 PM
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    Stop Setting Back

    I guess your installer didn't do a good job of explaining how outdoor reset works. The boiler via an outdoor sensor is monitoring water temp based on the outdoor conditions.\

    If your system was designed for the boiler to produce 180 degree water on your coldest day to keep the room 70 degrees it will. What happens when you set back is that the boiler doesn't know you set back the thermostat. It's trying to provide the water temperature needed to maintain 70 based on the outdoor temp and nothing else. It will not cram the space with heat to over come the set back. Some condensing boilers have a boost feature which would have to be set up by the installer.

    I agree with the others as to what was is the heat loss of the structure but you also need to understand how outdoor reset works.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Rob Blair Rob Blair @ 5:55 PM
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    Solution boilers do not have outdoor reset. NTXT

    Rob
  • Paul48 Paul48 @ 8:20 PM
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    Hmmm

    The I&O seems to say otherwise.
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