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Wall Hung vs Cast Iron Propane Fired Boiler

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Joe107
Joe107 Member Posts: 27
I recently posted about my oil direct vent boiler that cracked and several people were kind enough to reply. This is a follow-up on that. I saw a few discussions about wall-hung vs cast iron but the newest was a few years old so I thought I'd make this post.

I have a 15 year old home with a 12 zone Ultra-Fin high temperature radiant system and a 50 gallon indirect water heater. I am finishing most of my basement so there will soon be a 13th zone with a total of 22' of baseboard radiation. We went with the oil direct vent boiler when we built and did not build a chimney. My boiler (a Crown) cracked about 2 weeks ago. I was told by an installer and again at my local plumbing supply that it will take about 6 weeks to get a replacement. I am leaning towards switching to propane due to a few reasons such as having had soot twice on the exterior of the house, being able to get the oil tank out before the basement is fully finished, but primarily because of the fear that when the new boiler needs replacing it may not be kind enough to break in May. I'm also concerned about the future availability of ODV boilers given that they are not as common now as they were 15 years ago. Crown, for example, no longer makes them.

I did another heat loss calculation using Ultra-Fin's software and came up with 78,300 btu for the house and the heated area of the basement. I'd like to keep my existing indirect and set it up with priority with the new boiler. My current boiler has a net output of 100,000 btu and I am planning on going with a replacement with a net output of 80,000-90,000 btu.

I'd like to know which would be best for my situation, a heat only wall-hung or traditional cast iron? A few concerns I have about the wall-hungs are 1) higher tech, 2) parts may not be on the truck or at the shop in the event of a breakdown, and 3) will it condense and realize its full efficiency with my high temp system (we've run it these past 2 winters with a high limit of 165 degrees down from 180 degrees previously), 4) shorter life expectancy. Pros are 1) lightweight, 2) gain some floorspace, 3) some models cost less than cast iron boilers.

Also what brands do you recommend? My local plumbing supply carries US Boiler, Weil Mclain, Navien, Rinnai, Triangle Tube and Lochinvar. Crown is also a possibility because my current boiler is a Crown and the heat exchanger is still under warranty, they indicated they could give me a break on the price of a propane boiler.

Thanks for your time,
Joe

Comments

  • hot_rod
    hot_rod Member Posts: 22,468
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    What temperature do you need to supply on design day?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • random12345
    random12345 Member Posts: 469
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    Average weekly propane and ULS B2 heating oil prices in Pennsylvania. It's my understanding that all heating oil sold in PA must contain 2% biodiesel and have sulphur content < 15 ppm. Propane price has been adjusted to be energy-equivalent to a gallon of heating oil. 2% biodiesel HO = 138279.4 btu/gallon, and propane = 91410 btu/gallon according to GREET. Price series source: https://eia.gov/dnav/pet/PET_PRI_WFR_DCUS_SPA_W.htm

  • hot_rod
    hot_rod Member Posts: 22,468
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    12 zones or 12 loops?
    Fixed output boilers can run inefficiently on partial load conditions. Short cycling can drive boiler efficiency way down. We have seen examples of 50% efficiencies on short cycling boilers

    Mod cons can modulate to wide load ranges while maintaining 85- 90% efficiencies 

    any other appliances you might want to run on LP?  Range, dryer barbecues?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2
  • Joe107
    Joe107 Member Posts: 27
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    @random12345 That chart is making it look a lot worse than I thought it was. If I had a chimney I'd stay with oil. I don't have room to build one on that wall and I don't want to have a stainless steel one installed.
    I had run a calculation using pricing from about a week ago, our typical annual usage and 95% efficiency for propane and the cost of propane came out to be about $40 more for the year. But the historical chart tells a lot more. I can't figure out how to recreate it. The link takes me to the screen below but then I haven't been able to find the price comparison. Can you provide some more info? Thanks.



    @hot_rod I used a 70 degree design temp. We have 13 zones with the basement and 14 loops. Short cycling has been a problem. When I brought it up to my service guy he suggested lowering the high limit to 165 which we did. We do have a propane fireplace and a whole house generator running off of two 100-gallon propane tanks. Unless we had a long power outage, 75 gallons a year of usage would be about typical for us on those. If we switched to propane heat I'd get rid of those tanks and get a little cost savings from a lower price per gallon for filling a larger tank.

  • Joe107
    Joe107 Member Posts: 27
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    @random12345 Never mind about the chart. I exported the price data to Excel and recreated it. This complicates things a bit.
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    They are all well made.  Check out Viessman too, the one everyone else emulated as far as performance.  Word of advice: whichever brand you DO pick, purchase the parts kit at the same time so u can take THAT issue off the table.  See what the most professional company or guy in your area uses.  See what he likes and services.  As Hot Rod 🔥 says, a Mod Con will match heating loads with the greater turn down ratios than a old school boiler.  If you're handy, consider taking a class on maintaining the unit you have installed.  Save a few hundred bucks a year!  As Dan always said:  "That leaves more money for Beer 🍺! "   Mad Dog 🐕 
    GGross
  • yellowdog
    yellowdog Member Posts: 159
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    your propane boiler will not run at 95% efficiency with the high temp water your system requires. it will average out closer to 89% for the year. with todays prices on oil and propane being so close together, you will spend more than $40 extra per year heating your house with propane.
  • random12345
    random12345 Member Posts: 469
    edited May 2023
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    @Joe107 How many gallons per year have you used on average last 5 years? You may want to ask your oil company to email you an invoice so you know for sure. What is the model number of your current Crown boiler? Since I don’t know where in PA you are, I couldn’t be more precise with those numbers and your local prices may be different.
  • Joe107
    Joe107 Member Posts: 27
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    @Mad Dog_2 Thanks for the info, especially buying the parts kit. I will look into the classes. I like being able to fix what I have in my house. We'll see if they let me attend!

    @yellowdog Thank you also for that info. I was afraid that it wouldn't reach full efficiency.

    @random12345 We use about 780 gallons a year. My boiler is a Crown ODV-100, 119,000 DOE btu, 103,000 net. AFUE is 83.1%.

    I guess to sum it up there is no good answer here. The mod con is the better choice for my application but it won't realize full efficiency and I'll be paying more with propane.

  • hot_rod
    hot_rod Member Posts: 22,468
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    There will be a % of the year that you can run swt below 165°. Anytime the bopiler is running with the return to it below 125 or so it will condense. Under those condition you will get into the 90% +efficiency range. You could do some number crunching to predict what % of the year the boiler will be condensing.

    The bigger win with that many zones will be the modulation. Much less wear on a boiler if it is not banging on and off all winter long with short, inefficient run cycles.

    If you go with a mod con get a model with all the control functions, not the entry level models. Then you can really fine tune a system. I like the Lochinvar Knights

    ODR, step fire, boost, rate limiting are features that allow you to match the system perfectly.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
    edited May 2023
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    It also depends how your baseboard was sized. Many times it's more than required and you can heat the space with much lower temps which Mod Cons thrive on.  I've done a few jobs where I went with Wall to Wall High Output Slant Fin Baseboard and The Buderus GB142 Mod Con with ODR and we were heating the house comfortably with 140-145 degrees.  Homeowner reported about 40% savings over a standard, cast Iron  gas hot water boiler with convectors.  Mad Dog 🐕 
    Hot_water_fan
  • random12345
    random12345 Member Posts: 469
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    I have no idea what the right answer is here, but no matter which option is chosen, wouldn't it make sense to install a buffer tank regardless? And wouldn't that basically eliminate short-cycling and inefficiency whether a mod-con or cast-iron is used? It also seems like the lack of a buffer used with low temperature radiant may have caused his boiler to fail in the first place.
    The other question I have is if he doesn't like the DV on the side of his house, is it acceptable to have the PVC exhaust vent go up all the way past the roof line and then wrap it in Armacell so the flue gases don't freeze in the Winter?
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    No to the PVC vent...Most codes want polypropylene or CPVC. Besides being bad practice, it would be very unsightly to run it up the side of a building and put Armaflex  on it.   Mad Dog 
  • random12345
    random12345 Member Posts: 469
    edited May 2023
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    If the aesthetic appeal is a non-issue, and you're using PP or CPVC, why is it bad practice? I would prefer to have those flue gases not be next to my house where it could go in an open window.
    @Joe107 https://efficiencymaine.com/at-home/heating-cost-comparison/ My new favorite calculator. Hit the check box to change the details for the Propane and Heating oil Btu's per unit, the system efficiency, and play with the prices. This is for an annual heat load of 92 MMBtu which is just slightly more than your 89.63 MMBtu average. I don't know how much a gallon of oil or propane costs for you right now, but using $2.89-3.49/gallon for oil and $2.92/gallon for propane, 83.1% AFUE oil boiler and 95% AFUE LPG boiler, propane is $332-866 more expensive, and that's only if you get the nameplate rating.
    Mad Dog_2
  • realliveplumber
    realliveplumber Member Posts: 354
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    The venting has to be installed as per the manufacturer's installation instructions. Thats how it was tested, listed, and labeled. No manufacturer will allow it to be run up the side of the house.

    You could run it up the inside and through the roof. Maybe a closet, or a chase?
    Mad Dog_2
  • Joe107
    Joe107 Member Posts: 27
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    @hot_rod @Mad Dog_2 Thanks for the boiler info. Two questions for you guys, what is SWT, and, with these boilers are you able to set a high limit of say, 145, for space heating and a higher temp limit for when the indirect calls? If so we can try that.

    @random12345 Does the buffer tank sit between the return manifold and the boiler? What size tank is generally needed? Are they insulated? Is there also a mixing valve needed between the tank and the boiler? Sorry for all the questions.

    I'm ok with the dv on the side of the house. Problem with my current system is that I had to scrub soot off of the siding twice but that shouldn't be an issue with propane. I pictured it being something like this:



    This is similar to what's on my neighbor's house which has propane heat. PVC and installed when the house was built about 10 years ago. I'm aware that it has to be a certain distance from windows and sources of ignition.
  • hot_rod
    hot_rod Member Posts: 22,468
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    A buffer tank decision could be based on how the smallest zone matches the boilers-lowest turn down. That would be the condition to cause cycling headaches.
    Buffers for modulating boilers end up being fairly small, maybe 20 gallons or less. Still some $$ involved.
    The GV had a return protection valve built in, so it could run at low temperatures and was a good radiant ,cast boiler.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2
  • random12345
    random12345 Member Posts: 469
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    No idea about the buffer tank. That's why I asked the question. And @hot_rod answered it. I was just reading this issue of idronics that you linked to a while ago Mr. Rohr, great stuff. https://caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf
    PC7060
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    Exactly, thats where I'm coming from with the Exposed venting up the side of the building.  I've never read a Code that "encouraged" that and manufacturers instructions never suggest that.  I've seen that in Ireland 🇮🇪 in very old homes stone walled homes where plumbing was added 
    And they ran it exposed on outside walls.  Not only does it now look good, but Plastics, like Mod Con Vents, degrade in UV light,  aka The Sunlight...I had no choice a few times doing Rinnais in an Small appart building.  The only place to vent the Rinnai was in to a shared small 15 by 15 courtyard/air shaft
    That the apartments looked out on to.  Another installer just popped it through the wall and he was a happy camper..venting in to this courtyard.  I could not and would not do something so thoughtless and dangerous.  We ran it up 4 stories on the outside wall to the roof.  We couldn't get an extension ladder in to the courtyard, so we harnessed up the tough skinny, 125 lb Polish lad and lowered him slowly down by hand...us two 220 plus guys  to put the sections together, strap them to the block wall, drive 3 SS  set screws on each section.  The courtyard didn't see much sun at all so I wasn't worried.  The Brave lad got extra beer 🍺 that night!  Mad Dog 🐕 🤣 
    random12345
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
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    No soot with Propane or natural gas unless you gave MAJOR combustion problems.  In our region, you need to gave intake and exhaust 30" off grade to be above your high snow mark.  I see this ignored all the time....scary.  mad Dog  🐕 
  • Joe107
    Joe107 Member Posts: 27
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    @Mad Dog_2 I never would've thought rappelling down the side of a building was part of the job description! You should buy him another beer!

    Thanks again to all who replied.