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Replacing Burnham Commercial 808HE: same unit vs two smaller condensing boilers vs heat pumps

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yanks10123
yanks10123 Member Posts: 11

I have a 10 year old Burnham Commercial 808HE that has a cracked heat exchanger and was dripping water onto the floor during heating season. Can’t find the cause of the premature failure (no known leaks and no other makeup water) but, fortunately, I made it through the winter and have some time to sort out next options.

I’m looking for recommendations re: the following options:

(1) have the same boiler installed again

(2) replace with two smaller condensing boilers (local HVAC company recommended Navien NHB-150H)

(3) replace entire HVAC and do heat pumps with small gas boiler (huge investment but I have a large solar array that helps in the long run)

Background: located in Westchester, NY. House is 10 years old and has hydronic heat with 5 air handlers (2 in attic; 3 in basement) and air conditioning through the same air handlers. According to my local HVAC company, manual J says current boiler was slightly oversized but fell between the 807HE and 808HE

Thank you in advance

Comments

  • Hot_water_fan
    Hot_water_fan Member Posts: 1,899
    edited May 28
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    First things first, you need a heat loss. I do not place much faith in an installer’s manual J. How much gas do you use per year? I'd expect a 290kbtu heat loss home to consume about 7000 therms a year in that part of NY. Is that in the ballpark?

    Second, the heat pump option is a heating and cooling option, whereas the other two are just heating. Be mindful of this and make sure you’re comparing apples to apples.

    Third, this is nonsense and why you need a real heat loss:

    According to my local HVAC company, manual J says current boiler was slightly oversized but fell between the 807HE and 808HE

    The 807HE outputs 275kbtu. According to this installer, that’s too small. Yet, they are proposing two Navien 150s, which, when paired with air handlers, probably wouldn’t reach 275kbtu (that’s implying at LEAST 275/300 = 92% efficiency on the coldest day of the year, more so since “275kbtu is too small”).

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,764
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    No Navien's.

  • yanks10123
    yanks10123 Member Posts: 11
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    Ha, seems to be the consensus around here. What would you recommend? Thank you

  • hot_rod
    hot_rod Member Posts: 22,382
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    The load calc first. Then look at the various air handlers see what the output is a lower supply temperatures and how it matches your load and location.

    A hybrid system could have a A2WHP and boiler backup. That seems to be the direction the boiler manufacturers are going.

    I like the Burnham Ambient hybrid packages, boiler and HP with the control module.

    https://www.caleffi.com/sites/default/files/media/external-file/Idronics_25_NA_Lowering%20water%20temperature%20in%20existing%20hydronic%20heating%20systems.pdf

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • yanks10123
    yanks10123 Member Posts: 11
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    I have 4 Aspen AFM364 air handlers, 1 Aspen AFM254 air handler, and 1 modine garage heater.

    For AFM364 (3 coil), at 120, 140, and 180 degrees it's 31k, 33k, 70.6k BTUs. For AFM254 (3 coil) at 120, 140, and 180 degrees, it's 26.1k, 37k, 59.3k

    I'm out of my league on the manual J, and as Hot_water_fan rightly pointed out, seems like so is my HVAC person. I'll have to find someone else locally who can assist. Unfortunately, I don't have gas usage available - I've lived there for less than a year and the gas company screwed up my bills

  • hot_rod
    hot_rod Member Posts: 22,382
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    if the home heats comfortably with those fan coils, assume they are adequately sized


    using their highest output number

    3 x 70k and one at 59k comes out to 269k

    So a boiler at 269,000 output is all you need, thats all the air units can move into the home

    There is a good chance those units are oversized. One simple test, do they shut off on the coldest days, while keeping the home warm?


    any energy audit companies around you? You really need an accurate heat and cooling calculation to make the best decision

    A tape measure and spreadsheet is about all you need to do load calcs


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • yanks10123
    yanks10123 Member Posts: 11
    edited May 31
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    Thank you, @hot_rod. I have 4 of the larger air handlers so it’s 4 x 70 + 59k for a total of 339k (excluding the garage modine heater). Does that change your view?

    For whatever it’s worth even on the coldest days, the boiler had no trouble keeping up and the air handlers would shut off while keeping the home warm.

    Good idea on reaching out to an energy audit company —- I’ll do that.

    Thank you again

  • Zman
    Zman Member Posts: 7,588
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    Neither the condensing boiler nor the heat pumps are going to live up to their advertised efficiency unless you can lower the water temps significantly for most of the year.

    Doing a heat loss calc and comparing it to the output ratings at different water temps will help decide. If the boiler is on it's own gas meter, you can take your annual gas usage and divide it by the heating degree days in your area. A good energy consultant can look at the math in several ways and give you guidance.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 22,382
    edited June 9
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    the question would be, is the load actually 70k for all those air handlers?
    That is what a load calculation would clear up.

    Is it possible the load is 50k or less on some or all of the air handlers?

    The output of the air handlers is based on the fluid supply, the delta T, gpm and air flow across the coil.

    If you look up the output sheets you usually find a chart or graph showing the actual output under different temperature and flow conditions


    even if the hydronic side is running at max output condition, the air side needs to be able to move the btu also. So duct sizing and blower speed are part of the equasion

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream