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Thread: Boiler help

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  1. #1
    DIY Junior Member Steve Lanham's Avatar
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    Default Boiler help

    To the point. . Replacing a oil boiler to gas. Considering the Pioneer with indirect . The pioneer versa combo or the Columbia Power vent I think it's CSVB. Has anyone had experience with the pioneer boilers. The warranty is 12 years where as with the Columbia the warranty is life time...I live in Baltimore , 1800 sq ft 1932 medium insulated. Burnt about 500 gal a year...two contractors both suggested 150k for boiler size,, any suggestion is appreciated. Thanks !!

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    In the Trades Tom Sawyer's Avatar
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    Unless you live in an Un-insulated mansion I suspect that 150k is about twice as much boiler as you need. Not a Columbia or pioneer fan either. Look into Biase, buderus, lochnivar, something that is a two or preferably three pass boiler.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    Retired Defense Industry Engineer jadnashua's Avatar
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    It would be a leaky old barn conversion that needed 150K btu...Find someone to actually do a manual-J heat load analysis on the house, room by room, you may have to pay for this, but it will save you lots of money in the long run, and you'll be more comfortable with a longer lasting system. When it's too big, it short cycles...cycles are the killer, not running all the time. Ever had a light bulb fail while it was already on, verses when you turn it on? Almost never. Slightly different issues with motors and burners, but things get stressed each time you cycle it...a right-sized boiler is as good as you can get on this, and it's highly unlikely that 150K is right. Lots of threads here discussing the same issues, some before buying, some after and trying to fix it.
    Jim DeBruycker
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    In the trades Dana's Avatar
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    150K is an INSANE oversizing factor for your true heat load! With an indirect you could probably get along just fine with a 35K boiler!

    The 99% outside design temp for Baltimore is about +15F. Assuming a typical heating/cooling balance point of 65F (typical for non-superinsulated houses) that's 50 heating degrees below the balance point.

    A typical heating season in Baltimore is about 4600 HDD base-65F

    500 gallons over a 4700 HDD is (500/4700=) 0.106 gallons per heating degree day.

    A gallon of heating oil has about 138,000BTU, and assuming a steady state combustion efficiency of your oil burner is about 85% (could be, but it's probably lower), that's delivering (0.85 x 138,000= ) 117,300 BTU/ gallon. So per degree-day thats (0.106 x 117,300=) 12,434 BTU per HDD being delivered to the heating system.

    With 24 hours in a day, that's (12,434 / 24=) 518 BTU per degree-hour. So with 50 heating degrees at the 99% outside design temp you're looking at a heat load of about (518 x 50=) 25,900 BTU/hr.

    And that's probably an overestimate, since the odds of your oil boiler actually delivering 85% isn't high, and we haven't accounted for distribution losses on the system or hot water heating (assuming you're heating hot water with oil.) Odds are pretty good your true heat load is around 22-24KBTU/hr, and there are probably cost effective ways (even with cheap natural gas) to reduce it.

    Even a tiny 2-plate 35KBTU-in ~80% efficiency cast iron boiler delivers (0.80 x 35,000=) 28,000BTU/hr, which gives you ~10% margin even if your oil boiler was really running 85% AFUE (not likely) and is probably closer to 30% margin on your space heating load. That's also about the output of a standalone gas hot water heater, and if you zone the indirect as "priority" and size it for your biggest tub-fill you'll have equivalent or better performance of a standalone gas heater.

    The HTP Pioneer is a nice unit, but it's probably way overkill. If you go that route, the smallest of the bunch (PHR100-55) with the 35-100K burner would be an OK match, and is enough burner to deliver the "endless shower" experience. It would never modulate on space heating loads, since it's min-fire output is more than your heat load on the coldest day of the year, but since it's inherently self-buffering you'd be free to microzone the hell out of the place without risk of short-cycling.

    Got a link to the Columbia units you were looking at?

    It's probably cheaper to hit the same performance point with the AO Smith Vertex (the smaller 76K burner version) or smallest Polaris hot water heater and a plate-type heat exchanger for the heating system loop.

    Whether you'd be able to run the system at condensing temps and still deliver the ~20-25K of heat on design day is an open question- depends on the amount & type of radiation you have. If your system has big old-fashioned cast iron radiators, and was installed before the house was insulated odds are pretty good you'd never need more than 135F out of the boiler, and would likely get at least 90% average efficiency out of it. If you need 150F or more out of it odds are you'd be better off with a 2-3 plate mid-efficiency cast iron boiler with internal smart controls & outdoor reset, which should deliver an honest 85% when tweaked in, and a separate indirect. It just depends.

    What sort of radiation (total amount & sizes) and how many zones?

    [edited to add]

    Do you have a mid or late-winter oil bill with a "K-factor" stamped on it? The K-factor number is heating degree-days per gallon, and using the K-factor on a late winter fill-up would be a more accurate way to measure the true heat load. The nameplate BTUs in/out on the existing boiler would also be useful for making that calculation.

    Some years are colder or warmer than others, and I know the 500 gallons probably isn't a very precise number either, but most 2x4 framed homes with retrofit insulation and storm windows (or middle-of-the road double-pane replacement) will come in between 12-15 BTU per square foot of conditioned space @ +15F outdoor temps, and almost never over 20 BTU/ft unless it has major air leakage (which can usually be fixed for cheap.) If you have any single-pane windows it's worth installing tight low-E (not cheaper clear-glass) storm windows, which which usually pay back in 5 years or less- faster than the lower-cost clear-glass windows, and make the place a lot more comfortable, both winter & summer.
    Last edited by Dana; 07-18-2013 at 08:20 AM.

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    DIY Junior Member Steve Lanham's Avatar
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    Great forum!! Thanks to all...I've read some of the other threads about sizing. I find some of the figures confusing. I have big cast radiators measuring 682 sq. feet. That was counting the tubes and sections. Not sure what the K factor is. My old oil boiler was a converted coal monster. Someone said it was about 70% efficient. I have gas right next to the boiler feeding 2ea. 50 gal HWH. Changing to 1, i guess 50 gal. indirect. I do have insulation in the walls and old storm windows. Its the blown in type insulation. Columbia boiler recommended the Pioneer because of my chimney. At least 3,000 to reline and could end up being more. Columbia recommended the installer too. Seems like he knows his stuff. He still was thinking 150k because of the indirect....The Pioneer boiler is about 4,000...indirect HWH 1,500...Mechanic wants 10,000 about to do the job..Thats everything.... Plus I have to get rid on the old asbestus boiler for another 1,000. Getting very pricey...PS...2 ea. 50 gas HWH= 2 family house..One
    zone...

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Unless you're running a spa and need hot water in large quantities constantly, it's stupid to size the boiler for the indirect plus the space heating...you install the indirect as a priority zone, and while it is reheating the water, it stops heating the house. You almost would never know that happened - worst case, the house cools off a degree while that happens, then recovers. A typical WH only has around a 40K or so burner and those aren't very efficient, so maybe 32K going into the tank. About the smallest boiler you'd likely install is a 60K at maybe 95%, or 57K, nearly twice as big - they recover quickly, plus, you often don't drain the whole thing. You might want a 60g indirect, but it would depend on how many bathrooms and simultaneous uses there's likely to be. Read up on waste water heat recovery units (lots of discussions here), and if those hot water uses are for showers, you'd likely never run out if you installed one or more depending on layout and typical use. THey only work on things like showers, but they minimize the hot water you use by making the cold warmer to the shower so you don't need as much hot.

    Get a modcon boiler or other closed combustion boiler, and you vent it out the sidewall...don't need the flue anymore and can seal it up, or tear it out. Not having that there is one less air leak, and often a big one. Most closed combustions boilers use PVC plastic piping as the air inlet and outlet - cheap. Usable because the boiler extracts so much of the heat, the exhaust is cool enough for the plastic pipe.
    Last edited by jadnashua; 07-18-2013 at 06:57 PM.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    What Jim said- a smallest-in-class mod-con + 50 gallon indirect would typically run on the order of $10K installed as a retrofit, and sizing the boiler output for massive domestic hot water is just ludricrous, unless you actually HAVE a need for that much hot water. Scrap the chimney- seal it up, and only go with power vented, since it's clearly oversized for any right-sized combustion appliances.

    A 2-3 plate mid-efficiency cast iron beast (even a power vented sealed combustion version) + indirect would usually be under $10k. The ~70K-in Peerless DE-03 or Burnahm PVG3NI-BS would be on the big side, and still ~$2K for the boiler itself. The New Yorker PVCG30NI-T2 is a 62K-in, running under $2K. I'm not sure who if anybody is still making a 2-plate power vented cast iron, but ~50K would definitely be better sized for your heat load, and still enough to deliver the hot water, provided you up-size the indirect (50 gallons isn't going to cut it for a 2-family.)

    The Triangle Tube Solo-60 or Peerless PF-50 and similar mod-cons run about $3K for the boiler, and have low-fire output sufficiently small to modulate for at least of the the winter at your heat load, and give you a true mid-90s performance when the reset curve is dialed in (provided you don't micro-zone the hell out of the place with only low-mass fin-tube baseboard for heat emitters and short-cycle it into lower efficiency and an early grave.) If you keep the system configured as a single zone system it'll do fine. Don't get pulled into the temptation to up-size the boiler for better hot water performance unless you really do the math on it. If you need more hot water since it's a 2-family, upsize the indirect, not the boiler. Any ~50KBTU/hr mod-con has nearly 2x the burner output of a typical 50 gallon tank, but if you have both sides filling a bathtub or showering simultaneously for more than 10 minutes you'll need more than 50 gallons of storage.

    What type of radiators/baseboards, sizes, lengths, etc?

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    DIY Junior Member Steve Lanham's Avatar
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    My radiators are 682 sq. ft. I measured the sections and tubes as instructed.12ea. radiators...At this point I,m willing to spend the extra cash for a mod con with a 60 gal. indirect single zone. Reading different articles and it seems lots of people have different ideas about the best boilers. I would like to have something efficient but with the duribilty of my old Winchester oil boiler. Also who can give me an accurate " J " reading. Does the Co. thats doing the change over offer that service or are there specailty Co. that do it. I,ve spaced around but have'nt nailed that down. So in a nut shell...1800 sq. ft. 1932 well built cedar shake original with aluminum siding over that. Wood lathe plaster walls. Blown in insulation. Older storm windows first floor. New replacement windows on second floor. Finished basement with electric heat thats not used to often. Finished attic that is also electric heat and also not used often. PS...glad i found this sight. Info feels genuine !

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