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Thread: American Standard Arcoliner - Control for Domestic Hot Water

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    DIY Junior Member olimazi's Avatar
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    Question American Standard Arcoliner - Control for Domestic Hot Water

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    I got an old American Standard Arcoliner oil fired boiler w/ tankless coil for DHW which we just converted to a 40 gal electric hot water heater.
    The coil is cut off - so no water feeds into it, the pipes have been rerouted to the water heater.
    However I still have the boiler on - I don't want to shut it down for the off season in fear of it not starting back up in winter.
    The plumber turned the control on the low side all the way down (100).
    I hear the boiler kick in once in a while - not as much as before though, since we are not calling for hot water through the coil anymore.
    My question is - should I just shut it down for the summer?
    Is there a way to adjust the controls to stop the boiler from maintaining the temperature for the coil part of the boiler?
    The plumber took one look at the inside of the controls and recommended to leave it alone.
    I take it in the winter the boiler will be running alot anyway and won't be kicking on often to keep the domestic water hot.
    Any suggestions would be appreciated.

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    In the Trades Tom Sawyer's Avatar
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    You can remove the wire from the low limit side of the aquastat which will keep the oiler from maintaining temperature however that old boiler is at least 50 years old and closer to 70 and it was assembled with push nipples so there is a good chance it will leak when it goes cold. The best thing you could do with it is send it to the scrap yard. A new boiler will save you a good 20% on your heating bill and probably closer to 40% Those old Arco's were pigs. The flue passages are big enough to toss a cat through. Does it still have the original Arco burner hung on it?
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member olimazi's Avatar
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    Default Arcoliner

    Hey Tom, can you explain to me how it would leak when it gets cold? Is it because the cast iron is thermally expanded when it's hot, and when it cools off will contract expose holes? Just guessing...
    The efficiency is 82% from our last tune-up, so I'm not going to junk it - never had an issue with it.

    So you are recommending I leave the controls alone and let the boiler maintain the domestic hot water temperature? I'm leaning towards this myself. I only hear it kick on once or twice a day now that the water heater is in.
    Thanks,
    John


    Quote Originally Posted by Tom Sawyer View Post
    You can remove the wire from the low limit side of the aquastat which will keep the oiler from maintaining temperature however that old boiler is at least 50 years old and closer to 70 and it was assembled with push nipples so there is a good chance it will leak when it goes cold. The best thing you could do with it is send it to the scrap yard. A new boiler will save you a good 20% on your heating bill and probably closer to 40% Those old Arco's were pigs. The flue passages are big enough to toss a cat through. Does it still have the original Arco burner hung on it?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Thermal expansion/contraction is greater the larger the temperature change...metal loses its resiliency the more it gets flexed - yours is quite old and has seen many cycles. Minimizing the changes minimizes the size change.
    Jim DeBruycker
    Important note - I'm not a pro
    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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    Quote Originally Posted by olimazi View Post
    Hey Tom, can you explain to me how it would leak when it gets cold? Is it because the cast iron is thermally expanded when it's hot, and when it cools off will contract expose holes? Just guessing...
    The efficiency is 82% from our last tune-up, so I'm not going to junk it - never had an issue with it.

    So you are recommending I leave the controls alone and let the boiler maintain the domestic hot water temperature? I'm leaning towards this myself. I only hear it kick on once or twice a day now that the water heater is in.
    Thanks,
    John
    Measuring 82% steady state combustion efficiency with a combustion meter is an absolute hard limit of what the thing would do with a 100% duty cycle, not an AFUE. The idle losses on that beast are gia-normous compared to new-school lower mass, better insulated, smarter controlled, boilers, made even more-so with the excessive min-temp it needed for the HW coil.

    With the coil and with typical ~3x oversizing of the boiler for the actual design-day heat load you're probably doing no better than 65% AFUE in a central NJ climate, and that's probably being generous. With the lower idling temp the standby loss will be less and you'll use less oil, but since you're not heating HW with it, your wintertime idle losses will be a larger fraction of the wintertime total, and you still won't quite hit 70%. With a new-school "90% AFUE" oil boiler you'll likely be in mid-80s for an as-used AFUE, but unless you have a large house/large heat load (Is this an un-insulated 2500' house with single-pane windows sans storm windows or a 6000' decently insulated house or...?) it won't hit it's AFUE test numbers even with the smallest of them, due to a lower duty cycle than used for AFUE test conditions. (The smallest burners have ~60KBTU/hr output, and most modest sized 75+ year old houses that are reasonably tight & insulated will have design day heat loads of only half that. Oversizing factor for AFUE rating is 1.7.) But going from 65% to 85% AFUE is huge- a 25% reduction in fuel use.

    Going from a possible (even likely) 60% as-used AFUE to 85% is more like a 35% reduction in fuel use. Tom isn't steering you wrong here.

    If you're hell-bent on keeping it, for a lot less money, installing an Intellicon HW+ economizer would bring it up to at least 68-70% as-used AFUE, for about a 12-15% fuel savings.

    If you have a reasonably open floor plan there may be a better economic rationale to putting an Intellicon on the beastie-boiler and spending $4-7K on a ductless mini-/multi-split air-source heat pump rather than high-efficiency oil boiler (especially if you don't already have air conditioning, since the mini-split does both.) Even if your electricity costs 20cents/kwh, a decent mini-split will run a coefficient of performance of better than 2.5 in a NJ climate, which would be equivalent to sub-$2 oil in your current beast or $3 oil in a best-in-class new school boiler. If you're electricity is more like the 15 cent NJ average it's like heating with $1.50 oil in your beastie-boiler.

    If you're currently using 800 gallons/year @ $3.50/gallon and the mini-split carries 3/4 of the load @ 15cents/kwh x a COP of 2.5, it's like getting at least a $2/gallon discount on the 600 gallons saved, for $1200 year lower cash outflow. (And you get a very efficient & quiet air conditioning system out of it to boot.) A new-school boiler that saved 35-40% would save you not quite as much money, but it would cost more up front, and provides no air conditioning benefit.

    If you know the burner sizing and have annual fuel use numbers and a zip code (for weather data) it's possible to come up with a realistic oversizing factor and as-used AFUE of this boiler based on duty cycle. (If your oil supplier stamps a "K-factor" on your bill, that'd be useful info as well, particularly for mid-late winter deliveries.)

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    In the Trades Tom Sawyer's Avatar
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    there are lot's of times when I wish that nobody ever gave the customer the combustion efficiency report because the number is often misleading at best. 82% is perhaps what the oil burners combustion efficiency is. Note I said perhaps because with old boilers with wide open flue passages, the stack temperature is low enough because of infiltration that you get an incorrect reading. The newer efficiency testers will also register excess air which is what is causing your numbers to be horribly skewed. In truth ( and I have your boiler in my lab so I know ) the actual efficiency is closer to 60% with the original burner and climbes to around 70% if someone put a modern retention head burner in it. I hate to hurt your feelings but your boiler is little better than a boat anchor and a very big boat at that. Seriously, get a quote on a Buderus or similar boiler and start saving the big bucks. do not put another dime into that pig.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member olimazi's Avatar
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    Default Old Beastie

    Dana, Thanks for the elaborate response. I found myself googling alot of the things you mentioned - including AFUE and the Intellicon optimizer.
    I'm a little hesitant to install this device only because the wiring for my boiler control looks like it was jerry rigged.
    To answer some of your questions:
    The house is 1400' ranch, 1960's, 2 zones heat, decently insulated, storm windows, double pane... we use about 600 gallons of oil in the winter, plus another 150 gal for the off season (when the tankless coil was in, remember now I have the electric water heater) - so off season should be about 50 gal I'd say, since the boiler is still maintaining DHW temp, but not being called for hot water anymore. All in all, it's like you say, about 800 gal/year.
    Zip code is 08876 and I don't have a K factor.
    On the heat pump - we currently have central air, so I'm not sure how cost effective that would be.

    Tom,
    60%, wow, now that has me worried
    I agree it's an oil sucking hog, but we're moving in a couple of years and I don't want to install a new boiler for the next guy
    Just trying to figure out how to save a few bucks on oil 'till we're out of the house.
    I'm thinking space heaters in the living room and bedrooms and insulating the basement which has no insulation. The garage is cold in the winter and my daughters room above is cold - her room is at the end of the loop and the baseboards are warm at best. Another issue I have.

  8. #8
    In the trades Dana's Avatar
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    Even with retention burner, that beast only makes 70% in raw combustion efficiency???

    Original burner or no, at 3x oversizing it's never going to break out of the 50s on AFUE, and may even be sub-50%. Keeping it in service (even as backup to a heat pump) is a crime!

    BTW: Does tossing a cat through the HX during operation improve or hurt it's efficiency measurably? ;-)

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