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Boiler input rating oddity

hydro_newbie Member Posts: 37
I was wondering if someone might be able to help me figure out what I’m missing looking at the ratings for these 3 boilers from Burnham/US Boiler: ES2, Series 3, and ESC.

ES24: 105MBTUH input, 89MBTUH DOE output, 3 gal water content, 354lb shipping weight
304: 105MBTUH input, 89MBTUH DOE output, 3 gal water content, 354lb shipping weight
ESC4: 91MBTUH input, 78MBTUH DOE output, 3 gal water content, 350lb shipping weight

Looking at the I&O manuals, all 3 boilers use the same part number for the heat exchangers, the gas valve, gas manifold, burner orifice, main burner.

It really looks like these boilers are all very similar with some differences related to exhaust venting and combustion air. But I can’t figure out why that would change the input rating significantly between the ESC and the others.

I’m asking about this as I’m about to have an ESC installed, and have been on the fence between an ESC4 and an ESC5. My heat loss on slant/fin (70deg interior, 0deg exterior) was 80MBTUH. Measured gas consumption over the winter extrapolated pretty well out to 80MBTUH. I’ve been leaning towards the 4, but undersizing is a concern. The 5 seems pretty oversized though. If the ESC4 is actually a 105MBTUH input/89MBTUH output, then I’d be comfortable with the margin I have relative to the heat loss, especially as I hope to have some additional insulation work done at some point.



    JUGHNE Member Posts: 10,561
    A parts list may include several models. Main difference could orifice size and/or how many.
  • hydro_newbie
    hydro_newbie Member Posts: 37
    Thanks @JUGHNE! I see now that the ES2 and Series 3 uses the same burner orifice (natural gas #47) while the ESC uses a different one (natural gas #49). That must be why the ratings on the ESC are lower.
  • kcopp
    kcopp Member Posts: 4,187
    You will not be undersized.... there is a good deal of fluff in the boiler ratings. install the 4
  • hydro_newbie
    hydro_newbie Member Posts: 37
    Thanks @kcopp. Is the fluff you're talking about even in the DOE output ratings? My big hang-up is that my heat loss seems to be about equal to the doe output rating on the 4, which doesn't leave any margin for pickup.
  • FranklinD
    FranklinD Member Posts: 399
    Go with the esc4. When I bought mine, the ratings in the catalog said 96k input, and when I opened the crate, the ratings plate said 92k input. It keeps changing (this was 3 years ago or so).

    In terms of "will it be enough?" I'd have to venture that it will be. My maximum heat loss is 70kbtu/hr at -17*f (the boiler's net heat rating is 68kbtu I believe, or close to it). The first winter with the esc4 we saw many days of -25f to -29f with very windy conditions, and our house is 103 years old with questionable insulation. The boiler had no problem keeping up and still had a noticeable off cycle every hour...so yeah...between fluff factors built into heat loss programs and the boiler ratings themselves, I'd bet the 4 will do you fine.

    I'm actually adding an indirect water heater to our boiler this fall and I have zero concerns about lack of heat despite having 3 women in the house who love long, hot baths and showers.

    One thing: the outdoor reset add-on is only worth the money if you have baseboard (hi-temp) emitters. It won't do any good with big cast iron radiators. Just my two cents...I bought it and it never did anything (my supply temps are 140-150 at the coldest times of year). Live and learn. Next boiler will be a mod con for sure.
    Ford Master Technician, "Tinkerer of Terror"
    Police & Fire Equipment Lead Mechanic, NW WI
    Lover of Old Homes & Gravity Hot Water Systems
  • hydro_newbie
    hydro_newbie Member Posts: 37
    Thanks for the info @FranklinD. It's helpful to have others' experiences to draw on. I also just realised this morning that I was being too conservative on the outdoor temp for design day. I was using 0degF, but I should be using closer to 8 or 12degF. I live just outside Boston, MA. That drops my design day heat loss to about 66k.