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New Navien NCB 240E combi not reaching desired heat

jk71590
jk71590 Member Posts: 8
I had a new combi 240E Navien unit installed a couple weeks ago that has been doing well on two of the three zones in my house but not able to keep up with one of the zones. A great family friend who owns a heating and cooling company was nice enough to really help us out on replacing the our 60+ year old cast iron boiler and water tank with this. I don't know much about boilers and it really bothers my DIY minded self. The zone that is not heating is 500sqft with a basement below and insulated attic above. Standard drywall on walls with insulation inside. Two 6x6 windows in the space as well as an entry door and stairway going to the other side of the houses upstairs part. This area has an 8 foot baseboard as well as a 16 foot baseboard on opposite walls. Judging based off how well the rest of the house is heating, I think it might simply be an issue with not enough heating feet. I've quickly noticed that the heat coming off of my baseboard units are not nearly as hot as my old gas burning water boiler. He currently has it set to not be using the outside temp until he comes back to make tweaks. I live in climate zone 5 and its been around 28 to 38 degrees over the past 10 days. My concern is that if it is not able to heat this area past 71 with mild temps, when it drops down into the single digits my heating will not keep up. I notice that sometimes the heat coming off the baseboards is substantial but other times, even though water is passing through, it has almost no beneficial heat being produced. I notice that the supply heat can go all the way down to 155 vs the 180 max it is set to. I am guessing this is due to settings of when the burner clicks on based on supply and return values? Please do not take this as me not being beyond grateful for everything our friend has done for us, I just want to understand this better without having to bother him for what feels like the 100x time. Thanks!

Comments

  • jk71590
    jk71590 Member Posts: 8



  • jk71590
    jk71590 Member Posts: 8



  • Ironman
    Ironman Member Posts: 6,323
    I'm confused: you say the zone is not heating, then you say it heats to 71*. Please clarify.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • jk71590
    jk71590 Member Posts: 8
    Sorry yes it is heating to 71 but tops out. I've had it sat to 73 to try and test the system. My thought was that if it could get to 73 in moderate temps outside, 70 would be easy when its 5 degrees out. Understand that is not exact science by any means but it worries me that 73 is not possible when 32 outside.
  • jk71590
    jk71590 Member Posts: 8
    Sorry should have added that it does heat just not to the desired temp. Last night it would not go past 69 at night time. 71 during the day
  • Ironman
    Ironman Member Posts: 6,323
    The outdoor reset (ODR) function of the boiler varies the water temp based upon the outdoor temp (the colder outside, the hotter the water temp and vise versa). So, if the ODR curve is set properly, and if you're now able to maintain 71*, then it will be able to do that at any outdoor temp.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 1,558
    @jk71590 I've merged your duplicate posts into one here. Thanks.
    President
    HeatingHelp.com
  • jk71590
    jk71590 Member Posts: 8
    Thank you for the information and thank you Erin for merging the threads. I looked for a way to move them but didn’t see how.

    Ironman, I appreciate the help! Could you help me better understand why it would not be able to keep up while the odr is disabled as it is right now? I guess I thought without the odr and the system set to max temp for the feed, it would function as my old boiler did. Never felt so confused on a piece of my home :) 
  • Ironman
    Ironman Member Posts: 6,323
    There could be several reasons why it would not keep up with the ODR disabled. You need to measure the temperature of the supply and return lines for that zone when it’s been running for about 15 minutes or more.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • jk71590
    jk71590 Member Posts: 8
    Thanks! So checking the supply and return on that loop I get 170* supply and 156* return. This seems very high for the return, no? The entire loop is about 70 feet with about 24 feet of fins / baseboards.
  • Ironman
    Ironman Member Posts: 6,323
    That's a delta T of 14* which is pretty reasonable for milder weather. Judging from that, the boiler is not your problem. It's in your baseboards: they're either dirty, blocked off or under-sized for the area they serve.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    jk71590
  • jk71590
    jk71590 Member Posts: 8
    Thank you Ironman! I got the thinking last night that my old boiler sat right below this room in the basement with it venting right up through the middle of the room. I believe it was giving off a good amount of heat in the basement before that was naturally rising through the room. I did a couple of the calculators and it looks like I should have closer to 34 feet of venting based on my room when I only have 24. Almost 30% too small but was probably being compensated for by the old boiler. Will be looking to add another baseboard on the one wall that does not have one. Thank you for the help on all of this!
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