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Complete new system on small house

MN_DIYerMN_DIYer Member Posts: 7
Hi all,

New poster, long time reader. Competent DIYer with experience in many construction fields. First time home owner, 1911 colonial that was foreclosed on in Minnesota. The old hydronic system needs to be completely replaced. I am going to be doing all the work myself (hopefully ), much to the dismay of many of you but keep that in mind. I have access to pros who will help me if I run into any questions running my lines. What I'm hoping to learn from the knowledgeable people on the forum is what boiler/system to go with. I like the idea of combi systems and have looked into the TT's and Navien's but am beginning to to think that it is not as good a deal for me. Having a 1300 square foot 2 story house it's just not going to save me enough money to go that efficient. Heal loss is between 52,440 and 40,760 btuh, depending on what quote I use. I have just purchased CI rads that will produce 48,066 and am open to adding more. Do I go with something like a WM CGi 66,000 and indirect hot water or is something like the Navien NBC-180 going to be ok. It's just the wife myself and the dog, and that's how it's going to stay. One shower, dishwasher and laundry. Plenty of room and access for all heating equipment (I already have lots of walls torn out from rewriting the house) Any input from you all would be great, thanks!


  • SWEISWEI Member Posts: 7,356
    CI rads that will produce 48,066

    Using what water temperature?  More really is better when it comes to radiation.
  • MN_DIYerMN_DIYer Member Posts: 7
    CI rads

    That was calculated at 170f to give me some room
  • GordyGordy Member Posts: 9,530

    is that going to be needed?
  • MN_DIYerMN_DIYer Member Posts: 7

    Not at this time, we have some window AC units that we will use if needed.
  • SWEISWEI Member Posts: 7,356
    Some room

    Above 180ºF?  I'd size them for 140ºF or lower if at all possible.
  • MN_DIYerMN_DIYer Member Posts: 7
    edited July 2014
    It's possible

    But that can be added or changed with no problem at this point. I want to get the boiler and hot water settled on first.
  • GoodRatsBrewGoodRatsBrew Member Posts: 8
    Complete new system on small house

    You should consider a Weil Mclain GV90+ for your house.
  • MN_DIYerMN_DIYer Member Posts: 7

    To be honest I haven't paid much attention this line, I don't know if the price increase is worth the 7% effeciency gain. I fear it would take too long for the ROI to payoff? Am I wrong or would it make sense to forget the indirect hot water tank and just go old with a properly sized 85% eff CI boiler and a standard hot water tank? The more info I get the more I think high efficiency may not be my best option... It looks like I can save enough money up front going "non-efficient" to cover any savings during the life of the boiler...?
  • MN_DIYerMN_DIYer Member Posts: 7
    Thanks SWEI

    I have increased the size of the rads now.
  • GordyGordy Member Posts: 9,530
    efficiency and ROI

    As far as the indirect you can make more hot water with the indirect verses conventional, and make it at the efficiency of which ever boiler you choose to use. So 80/85 I wont say 95% because a condensing boiler wont run in that range of efficiency while producing DHW.

    About the boiler and ROI. We can plan our ROI with present day utility cost, and say the ROI is not there. But what you dont know is future utility costs, and if anything will steadily increase.

    Your heating emitters are High temp 180 for now. You can decrease the required AWT by adding more radiation, or envelope upgrades, or both.

    The trick to get high efficiency mod/con boilers to play well with high temp systems is to

    get the emitter side of the system ready to recieve the mod/con. you dont need 180* but 1% of the heating season.

    If this country is ever going to get green, conservative, what ever you think the path is we ALL have to get away from the frame of mind whats in it for me only.

    ROI for high efficiency is not always black and white there is always some gray, and the gray is future energy costs. The question is does one want to be in a position to be ready for it, or wish they would have been.

    Im sure you have lurked in some recent discussion about this choice.
  • MN_DIYerMN_DIYer Member Posts: 7
    Thanks Gordy

    Thanks for reminding me to think about the future, I was getting to focused on the now. Envelope upgrades are on the plan for next year. I am repainting the house then and before I do that I am having insulation blown in through the outside walls.

    You are also correct that I forgot the length of the heating season and it won't all be as cold as it is in my mind. I also forgot that if I can get my RWT down then I don't have to worry so much about how I'm going to get down to condensing temp. I'm starting to turn into a yo-yo...
  • GordyGordy Member Posts: 9,530
    Envelope upgrades

    I would calc a heat loss with those intended upgrades to see how much difference there is going to be in the load.

    IF you are 100% sure those upgrades will take place. I would size the boiler to that heat loss. use the higher water temps until that upgrade happens then you will be poised for lower water temps after upgrading the envelope.

    What im trying to say is IF the heat loss proves to allow lower water temps with out increasing radiation. Then you may not have to add more radiation the envelope upgrade will take care of that for you.

    You wont know until you run the Futuristic heat loss. And only hang your hat on that IF you are sure that will happen.
  • Rich_49Rich_49 Member Posts: 2,546
    Delta T

    Also take into account that CI Rads play very well with 30 - 40* Delta T so with ODR you can be in the condensing condition for much of the year
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833

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