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Utica, NY Boiler (Water 116,500 BTU/Hr) with 2"/3" Iron Pipes to Navien Combi NFC Idea

walkingmyhouse Member Posts: 1
edited May 2019 in THE MAIN WALL
Afternoon, I love the forum comments, knowledge, and experience here. I'm a new house owner of a 1917 house, in Upstate New York, with a 20+ year old gas boiler to cast iron radiators. I've been looking to replace it with a combi boiler from Navien. I'd like the floor space when the Utica boiler is removed and the head room with the black pipes removed hanging in the basement.

Can black pipe be cut at the "beginning parts" going up into the 1st floor and copper make the connects from a combi boiler? The current black pipes all reduce to 1" pipe feeding the 1st and 2nd floor cast iron radiators? (I'm reading some people have trouble with combi boilers with iron pipe leaving iron particles in the combi boiler. The Navien NFC has a magnetic filter it appears to reduce this issue?) In a perfect world I'd enjoy a Navien combi boiler that runs copper to the 1" black pipes at their starting points leaving the basement ceiling. (I'd have the installers cut the 1" black pipe with 6" hanging down from the basement ceiling if an option.)

Upstate New York House
House SQFT: 1700
House Year: 1917 - Energy Efficient Windows, Good Insulation.
Always enough comfort heat for family of 4 and hot water for showers from a hot water tank.
Utica, NY Boiler (Water 116,500 BTU/Hr)
Piping: Black pipe - 1", 2", and 3" (Basement ceiling is open for full access.)
Cast Iron Radiators used in all rooms.

Navien NFC Specs - https://www.navieninc.com/series/nfc/downloads

Lastly, the black pipe has elbows with wrapped asbestos. I could re-wrap the elbows and cut away pipes but wondering if it's scrap metal then or a hazard for a company to handle? I assume it's a local issue ruling but if they'll going to the dump with them I can surely accomplish it too. Also I imagine the Utica boiler doesn't have asbestos but I'll double check with the company on that one and possible do an at-home test on it.

Please ask any questions, I've chatted with a people who would like to know some or all of these issues. Thanks!


  • Ironman
    Ironman Member Posts: 7,223
    edited May 2019
    What size Navien and how many bathrooms do you have? Any unusually large domestic load?

    Generally speaking, we don't recommend combi's because in order to get the burner large enough for domestic, it's way over-sized for space heating. This will short cycle the boiler and greatly reduce is life. Combi's also use a plate heat exchanger for the domestic which has very narrow passageways and will foul and clogged if you have any degree of hard water.

    If you left the old gravity piping, that, plus the mass of the radiators would give you a lot of buffer to prevent short cycling. Removing the large piping would probably remove about 1/2 your buffer.

    A much better scenario is a mod/con boiler + an indirect water heater. More $$ initially, but a lot less $$ and headaches in the long run.

    I really wouldn't recommend letting the average plumber or HVAC guy tackle what you're planning as most do not understand hydronic systems, particularly old gravity ones.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Ironman
    Ironman Member Posts: 7,223
    Also, you probably don't need more than 60 - 70k btu's to heat your house. You should do a scientific heat loss calculation and a radiation survey to determine your exact needs.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Steamhead
    Steamhead Member Posts: 16,459
    Ironman said:

    Also, you probably don't need more than 60 - 70k btu's to heat your house. You should do a scientific heat loss calculation and a radiation survey to determine your exact needs.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • BumpyHed
    BumpyHed Member Posts: 7
    The History we leave behind us is the History we Discover in front of us. My fellow Heat Men have spoken. Best of it with your project.
  • hot_rod
    hot_rod Member Posts: 20,790
    I'll speak up for the combis, I live with 3 of them, one is 16 years old. DHW requirement needs to be considered. Any large dump loads, lots of loads running at the same time? If so a tank style or indirect for sure.

    Most all Combis can be electronically derated on the heating side. I have two Lochinvar combos and have the burners locked at 30 & 50% fire. Ramp delay and anti-cycling are other functions available to dial the in and avoid short cycling.

    Full fire only for DHW call. Expect around 2 gpm for a 110- 120,000 BTU/hr. A 150,000 would get you around 3 gpm DHW and a 10- 1 turndown.

    They can scale up on the DHW side, generally with good flow rate on dhw draw they scour well. I have not descaled any of mine including the 16 year old one, 15- 17 gpg water. I'd add valves to make a quick descale process, Webstone for example.

    Tankless style water heaters scale more often because you have flame temperatures 320- 350F against the heat exchanger, so hard water scales out on the surfaces, and they may need yearly cleaning. . With combis the plate style HX runs around 180F, and the fluid channels are designed to be self cleaning.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bob eck
    bob eck Member Posts: 930
    Rinnai has a new combi boiler i series coming out.
    Two smaller combi boilers will deliver 4.1 GPM domestic hot water
    Largest model will deliver 5.1 GPM domestic hot water
    All GPM ratings are at 70 F temp rise.
    Rinnai says the combi boiler will do heating and domestic hot water at the same time.