American Standard Arcoliner - Control for Domestic Hot Water

[olimazi]

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.

[Tom Sawyer]

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?

[olimazi]

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

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?

[jadnashua]

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.

[Dana]

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.)

[Tom Sawyer]

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.

[olimazi]

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.

[Dana]

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? ;-)

[Dana]

You seem to have posted more info as I was typing...

Design temps for your area are around +10F, with a ~5000 heating degree day heating season, so based on an assumed 600 gallons of fuel use for heating we can put an upper bound on your design condition heat load to get a handle on oversizing factors:

source BTUs= 138000 BTU/gallon

At an efficiency 70%, 1-gallon delivers 138000 x 0.7= 96,600 BTUs to the house.

With 600 gallons and 5000 heating degree days, the house uses 600/5000= 0.12 gallons per HDD. (K-factor as used by oil heating guys is the HDD/gallon ratio, which would be 1/0.12 = 8.3 )

Per degree-hour that's 0.12/24= 0.005 gallons so x 96,600BTU/gallons = 483 BTU per degree-hour.

At +10F, you're looking at 65-10= 55 heating degrees, so times 483 BTU/ degree hour you're at ...

26,564 BTU/hr for a design condition heat load, (a credible number, maybe a bit high for a tight well insulated 1400' rancher at 10F) which is about half the output of the very smallest oil burners. If the combustion efficiency is 60%, your actual heat load is more like 22.7K. If (defying available information to the contrary) it really IS 82% would be ~31K ( but I don't believe that for a minute.)

I expect the beastie-boiler's output is north of 100K, so assuming you're in the 25K range for heat load you're at least at 4X oversizing. Using NORA's FSA calculator tool selecting "old boiler with tankless coil" adjusted to 100KBU output and 64 gallons/day their heat load estimate is about 20KBTU/hr, and your AFUE is about 49% based on 800 gallons/year usage. That estimate may be low, but if so, it's not by much.

At 50% efficiency and $3.50 oil that's 2x $3.50/138=5.1 cents per 1000 BTU. 15 cent electricity is 15/3.412= 4.4 cents per 1000BTU - electric space heaters are literally cheaper.

With a 20K-25K heat load even the smallest Buderus would be 2-3x oversized. Swapping out the AC for a 2.5 ton multi-speed R410A-refrigerant heat pump & variable speed are handler would have the same order of magnitude upfront cost, and lower operating cost. A 3-head 2-2.5 ton multi-split would be more efficient than a ducted system and significantly lower cost, if that works with your floor plan.

Insulating the basement is a good idea, but it's not free either, and it would take the whole-house heat load. If you go that route you have to protect the foundation sill from rising damp from ground moisture, which means no interior vapor barrier, and any studwall needs to be protected from condensation on the studs. The cheap way to do this is to put 1" of rigid XPS insulation up against the foundation wall (seal the seams with duct-mastic), trapping it tight to the wall with a 2x4 studwall with UNFACED R11 or R13 batts. XPS is sufficiently permeable to water vapor to allow the foundation to dry toward the intetior rather than wicking moisture up to the foundation sill, but has sufficient R value that it's interior surface doesn't stay below the dew point of interior air long enough to create moisture problems from wintertime condensation. (You can probably even get away with 3/4" XPS, but half-inch would be pushing your luck.) Be sure to put a sill gasket under the bottom plate of the studwall to ensure that it doesn't wick ground moisture & rot.) It ends up being a ~R15 "whole wall" (thermal bridging included).

Alternatively, using 2-3" of unfaced EPS (white beaded insulation) held in place with 1x strapping through-screwed into the foundation with tapcons on which to mount the wallboard. That ends up at ~ R8-R12. It can be cheaper & easier than the XPS/studwall approach if you have a source for reclaimed rigid board scavenged from commercial roofing demolition/re-roofing. You may have to hunt a bit, but there are resources out there (craigslist.org seems to have several listing in my area). You can use recycled XPS too up to 2" (R10), but be very careful about using foil-faced goods of any type, as that can lead to sill-rot if there isn't a good capillary break between the foundation sill & concrete.

Whatever else you do (or don't), spraying 2" of closed cell foam to insulate and seal the band-joist and foundation sill to eliminate air leaks there is going to be worthwhile, and sealing it to the top of your new insulation scheme would also be key.

If there isn't currently insulation in the floor of your daughter's room, it's not very expensive to blow cellulose between the floor joists from below,and could make all the difference.

[Tom Sawyer]

Dana, from the picture and the age of the controls I would bet that the IBR input is 140,000. Now I'd bet that it's not fired at anywhere near that but when you down fire an old boiler with big flue passages it is another thing that leads to good looking combustion efficiency numbers because it gives lower stack temperatures.

To the OP. If you are not willing to change the boiler, my advice would be to turn the low limit down and walk away from the pig. It's not worth putting a dime into in either parts or labor.

[Dana]

Tom, ~140K or 1.0gph-in @ 70% efficiency is ~100K out, no? Throttled back to 0.8gph + one cooked-cat per day at ~60% efficiency is still ~65-70K out, and 3x oversized for the load.

While I understand the impulse for short timers to just leave the problem for the next owner to deal with, it's probably easier to sell something that doesn't look like a nightmare money pit of a project, and it'll be more comfortable to live in during the intervening (if short) years.

When I lived under a real slumlord 25 some years ago the hot air heating plant looked about that decrepit. I sprung for a (used) flame retention burner, sealed the ducts on my own labor & dime. I lived there for another 2 years, and never looked back. I probably didn't make the money back on fuel savings, but the system was quieter, didn't reek of unburnt fuel on startup, and I was still a happier (if still slummy :-) ) camper for having done it, and would do it again. YMMV.

An 86% smallest-in class lowest-end Buderus lists for $2K, say it's $6K, installed. Your 600-700gallons/year drops to 450-500 (or less), and at $3.50/gallon it's saving you $500-700/year (after taxes.) If you hang in for 3 years you're now out maybe ~$4K, but by having a new boiler unloading the house takes 30 days, not 180, and you're not beaten back $5-10K on selling price for leaving a dying pig in the basement, so you're possibly money-ahead. In the meantime you've probably been pretty comfy, especially if the installer deals with whatever flow or baseboard sizing issues exist in your daughter's room as part of the package.

You owe it to yourself to at least get some quotes- if it's a dead-easy install it could be even less than $5K. About three years back (before the economy crashed) I managed a situation for my in-laws on a rental property they owned with a failed steam boiler. It ended up about $7-8K whole new 2-zone, hydronic baseboard system including an indirect HW heater, with a 3-plate ~60KBTU gas fired cast iron boiler of similar list-price. Yours has to be a simpler/cheaper installation, by far. (Quotes for just replacing the steam plant were considerably more expensive.)

[Tom Sawyer]

I can pretty much guarantee the when it comes time to sell the house, that boiler is either going to get changed or a few thousand is coming off the sale price.

[wallygater]

Yes it is old. I think mine is about 60 years old. Yes it is a beast, about yhe size of a voltswagon bug. The one that I have is the same color. It is a steam boiler and has been working very well all of these years. Original everything. New oil gun. And it still produces the DHW through the origial built in coil. And yes, the rust inside this thing is unbelivable.

[Dana]

They're out there! I know several homes with steam boilers even older & far more decrepit than yours that still in operation. But at the current fuel prices there's not much sense in keeping them around. You're likely getting no better than 50% AFUE out of it during the heating season, whereas newer steam boilers will run an AFUE of 75% or better (some even hit the low-80s.) It might cost 6-8grand to swap it out, but a new one would cut your fuel use by more than 35%, maybe even half. (But in a L.I. climate a heat pump solution might be a better investment, even if it's more money.)

BTW: It looks like you're using the DHW coil as the heat source for an indirect tank. That's somewhat more efficient if you run the boiler only at low temp during the summer (or cold-start it), but if you're keeping the boiler at 150-160F your net HW heating efficiency is probably sub-25%.

[wallygater]

Hey Dana, I sure wish you lived on long Island. That goes for the rest of you pro`s out there.

My old steam boiler is heating the house very nicely. no banging, no problems. From what I hear, In order to replace it many things need to be taken into consideration. To big is no good, and to small is no good. It needs to be sized just right according to the house and the radiators.
I have read a lot about near boiler piping, and apparently, if that is not done correctly I will be wishing I had my old boiler back. Also, the new boilers are very small and don't have anywhere near the heat retention that the old has, due to its huge mass of iron.
I do love the indirect DHW tank idea. That would be a dream come true. What you see in the picture is only a holding tank, and it sucks. The boiler is still making all the DHW, and it disgusts me that it has to pass thru that 70 year old rusted up coil. Just to add some insult to injury, my chimney is also in bad shape. It needs to be re-pointed, its missing some bricks on the top, the mortar slope thing from the top is long gone, and it is in way overdue mode for a SS liner. My plan is to do the chimney first. Before the whole thing collapses on me. Hopefully, heating oil will some day come back down. I use about a 1000 gal per year.