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Replacing 30 yr old Polaris with Combi Boiler

BEK Member Posts: 3

Our 1900 sq/ft. home located in N.J. has a open single zone radiant floor system with oxygen barrier pex in the 1st floor (950 sq/ft. slab).

The 30 yr. old propane Polaris 100K -50 gallon heater needs to be replaced and we want to separate the DHW from the heating system during the process.

Home is well insulated with SIP panels, heating load 25K btu's. The 2nd floor rooms have electric baseboard heaters which are needed only on the coldest days.
There are 2 bathrooms, dishwasher & washer.

The heating contractor advised that using the new Polaris 100 K BTU's -34 gallon model is an option and would convert the system using a flat plate heat exchanger.

We need advise on options & models for combi condensing units vs buying another Polaris.

The utility room also has very limited space.



  • GGross
    GGross Member Posts: 1,105
    While I am not a big fan of using water heaters for space heating, it would seem this system was possibly done right as it lasted 30 years. Can I ask why you want to use a condensing combi instead of replacing with something comparable?
  • BEK
    BEK Member Posts: 3
    Thanks for your reply.
    Considering separating the DHW system from the radiant heat.
    Not 100% sure if its really necessary, as you know there's different opinions on the open system.

    Yes, the existing system worked fine, changed igniters more than a few times on the Polaris,
    probably in part because of the short cycling. It was oversized for the job, handled the radiant and DHW easily, operating cost was low.
    Original heating contractor & owner built the open system, similar to design sold by the by the Radiant Heat internet companies.

    Our heating contractor is on the fence as to which system to go with, has mixed experiences with different combi units.

  • Paul Pollets
    Paul Pollets Member Posts: 3,658
    I'd be using the Viessmann 222F Combi boiler. Small0 footprint and 3.5gpm of hot water with an integral 28g tank
    Alan (California Radiant) ForbesGGross
  • Alan (California Radiant) Forbes
    I like the Viessmann 222-F as well. Lochinvar and IBC make nice combi’s as well. 
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • psb75
    psb75 Member Posts: 863
    You have the option now to use the right machine for the job. Use a modulating, condensing boiler that makes domestic hot water and heating water--like the ones mentioned above.
  • BEK
    BEK Member Posts: 3
    Thanks for all your input. I will for forward suggestions to the heating contractor
  • hot_rod
    hot_rod Member Posts: 22,472
    You will get a lot more features in a combi compared to a Polaris.
    Two of us get by fine with a 120 combi.
    I think the Polaris was a 100K?
    Modulation, outdoor reset, step firing, rate limiter. All these features, properly adjusted, will tame a 120 boiler to a 25K heat load. 12K turndown on the heat side. Maybe a 3 gpm continuous DHW flow. Depends on incoming water temperature.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream