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Mod con and/or combi design help

agansley Member Posts: 6
Hello all has been awhile, I am a plumbing and heating contractor, I am not new to Mod cons but do mostly service and repairs, have installed several dozen over the years, but have a project that's giving me some design issues.

Northern New Jersey
3 story building, single gas hot water ci boiler, single zone of ci radiators. 1930 construction, single pane windows. 75 gallon gas water heater.
3 apartments total, 1st and second have 2 full bathrooms and 3 bedrooms so possibility of both showers going same time.

Customer wants:

1. Separate all 3 units heat and dhw.
2. Change to baseboard emitters, does not like the exposed piping and ci radiators.
3. get rid of chimney / make more room and save cost of liner.
4. Move boiler location to secure back mechanical room, he was thinking combi units
( room may be to tight for 3 boiler indirect combs)

Customer is a little flexible and willing to pay for the right job.

My issues, with quick math looking at 53,382 max load per larger unit, most likely on 2 zones.
Would like to stay with quality unit that has good support in the area, im not one to install and leave.
Problem comes in with a possible 4 gpm dhw of the two showers, and not sure if I would have enough room for larger indirect tank.

Thoughts on a particular unit?


  • SWEI
    SWEI Member Posts: 7,356
    Seem like a lot of heat for an apartment. How many square feet are they and when was the building built?
  • agansley
    agansley Member Posts: 6
    1930's building, large apartments, did not do a full heat loss calc yet, looking at approx. 1900 sq foot., but my problem is only going to get worse with less heat, my dhw demand far exceeds my heating demand, and where I would normally over come this with larger indirect, I don't have the room. Im not a combi fan, but wanted to look into the options before , I have another conversation with customer.
  • SWEI
    SWEI Member Posts: 7,356
    Natural gas? Utility rebates? Sometimes a separate tankless can pencil out better in those cases, assuming you can route all the flue pipes.
  • kcopp
    kcopp Member Posts: 4,255
    Seems a shame to put a combi all the way down in a basement away from where the hot water is needed. Can you put them in the apts? This one fit in a closet.
  • kcopp
    kcopp Member Posts: 4,255
    TT challenger 125.
  • Firecontrol933
    Firecontrol933 Member Posts: 73
    So the landlord wants to take out CI radiators that are as close to indestructible as you can get and install BB's that will not stand up to the average renter.
  • kcopp
    kcopp Member Posts: 4,255

    So the landlord wants to take out CI radiators that are as close to indestructible as you can get and install BB's that will not stand up to the average renter.

    Go figure..... brilliant!....... NOT!
  • Rich_49
    Rich_49 Member Posts: 2,738
    Is he planning 2 new gas meters also ?
    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
  • agansley
    agansley Member Posts: 6
    Rich apartments already have separate meters, I will have to run new gas lines to units no matter where they are located. kcopp I did consider possibly putting units in a closet on each floor and may still be a possibility, but need to find a suitable combi for that, will not be able to use an indirect tank, just not enough room. As for the the fin baseboard, I agree that baseboard does not hold up well with tenants, will be considering base ray ci radiators if I cannot convince owner to keep radiators.

    With all that can anybody help with my actual question.

    Thank you for any help.
  • kcopp
    kcopp Member Posts: 4,255
    I like the IBC DC 125. or the 160.
    Fewer parts so less to break down.
    Fits almost anywhere.


    As w/ any combi DHW load will make the heat load oversized....

    I am told they have another unit coming out this summer that will have a smaller heat load but a higher output DHW coil.

  • hot_rod
    hot_rod Member Posts: 19,844
    Pay attention to the DHW production at the lowest incoming water temperature in your area. I have a 120 Cadet Combi that sees well water no lower than 55F. It struggles to fill a tub with a basic 2 handle fill faucet.

    As with tankless i think most families would need at least a 160K unit. That can get lopsided with the heat load, however.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Snowmelt
    Snowmelt Member Posts: 1,394
    The Navien 240 will work as well as the rinnai e 110 will do the job i install both units last be 110 I did was in hoboken.
    if you want I could assist on this with you as I live in Linden and certified on both companies
  • agansley
    agansley Member Posts: 6
    Thanks Snowmelt, was considering the Navien 240, just trying to balance the idea that the lowest input is 18,000 btus which is a 1/3 of my total greatest load, don't want the unit to short cycle its self to death, but as hot rod pointed out, I don't think I can get away with the ncb 180, only getting 3.4 gpm @ 77 degrees. I know here locally I have a lot of support for the Navien units, and have installed quite a few domestic only units down the shore, How has the reliability been on you Navien combi installs?
  • agansley
    agansley Member Posts: 6
    Kcopp, thanks for your input, like the fewer parts idea, and looks like a great unit, just to big of a low end fire rating, and not much of a East coast US support.
  • Snowmelt
    Snowmelt Member Posts: 1,394
    my support been real good. Give me a call when you get a chance 908 247 7743 -George
  • jonny88
    jonny88 Member Posts: 1,139
    @agansley IBC have invested heavily in East Coast and have a large warehouse/training facility in NJ.If it was 2 yrs ago I would agree with you but now they have good support.
  • bob eck
    bob eck Member Posts: 930
    Each apartment has two showers. Install 1.5 GPM shower head. Max DHW each unit is 3 GPM. Most good combi boilers can deliver 3 plus GPM of DHW.
    What brand does your go to wholesaler stock and sell? Does the wholesaler stock parts.
    I work for F W Webb we sell Rinnai, Bosch, Navien and HTP combi boilers. Also Burnham is coming out with a combi boiler in May and I believe W/M will have a combi boiler later this year.
  • kcopp
    kcopp Member Posts: 4,255
    What ever became of this conundrum?
  • kcopp
    kcopp Member Posts: 4,255