Hello - new to the forum and to gas boilers in general. Recently moved into a house (built in '64) with an old Ack-o-Matic 21W6 gas boiler. Just today I replaced a White Rodgers zone valve head because the old one had a stripped gear. I know one of the burners doesn't fire. I had an HVAC tech come look at it and he said it would take a fair amount of disassembly to get the burners out. When this heating season is over I'd like to clean them as best as I can, but I'm not quite sure how to get them out. Does anyone have any advice on this, as well as any other literature on this boiler?
Ack-O-Matic Gas Boiler (21W6) Info
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This boiler is old enough to join AARP, won't operate even near it's nameplate efficiency for an as-used AFUE (it doesn't even have an automated flue damper!) and isn't really worth fixing. You can probably keep it limping along for decades but it's time to consider replacing it. Most cast iron boilers have a useful lifecycle of 20-25 years before the lower efficiency and higher maintenance makes it economic to move on, and you're more than 2x beyond that. Both the water side and fire side of the heat exchanger plates erode over time, resulting in less effective heat transfer, which adds up to a lower raw combustion efficiency. You could break the boiler apart completely to clean up the plates and gain some of the lost efficiency back, but that's never "worht it".
What are it's input & output BTU numbers (usually on a nameplate some where, often inside the cabinet.)
With this winter's gas bills and the nameplate efficiency it will be possible to come up with reasonable estimates of the size of the heat load, to size & pick out an appropriate replacement. Almost all boilers installed in the 1960s were 2-3x oversized for their actual loads, and that was BEFORE the house got tightened up with additional insulation & better windows. At 3x oversizing the oversizing factor alone becomes an efficiency problem, even for a new cast iron boiler. But tracking fuel use against heating degree-days for wintertime billing you can use the old boiler as the measuring instrument to nail down a firm upper bound on the heat load. Even if you put it off for a year or two, it's worth having that number figured out before swapping it out, since 9 out of 10 boiler installers would swap it for something with the same or even higher heat output "just in case". But the "case" that would actually require a 3x oversized boiler is an outdoor temp of less than -100F, a case that hasn't happened in Iowa since before the last ice age.
What are it's input & output BTU numbers (usually on a nameplate some where, often inside the cabinet.)
With this winter's gas bills and the nameplate efficiency it will be possible to come up with reasonable estimates of the size of the heat load, to size & pick out an appropriate replacement. Almost all boilers installed in the 1960s were 2-3x oversized for their actual loads, and that was BEFORE the house got tightened up with additional insulation & better windows. At 3x oversizing the oversizing factor alone becomes an efficiency problem, even for a new cast iron boiler. But tracking fuel use against heating degree-days for wintertime billing you can use the old boiler as the measuring instrument to nail down a firm upper bound on the heat load. Even if you put it off for a year or two, it's worth having that number figured out before swapping it out, since 9 out of 10 boiler installers would swap it for something with the same or even higher heat output "just in case". But the "case" that would actually require a 3x oversized boiler is an outdoor temp of less than -100F, a case that hasn't happened in Iowa since before the last ice age.
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Thanks for the reply. I'd like to keep it limping along for another year or two minimum - I'm well aware the efficiency is not helping my gas bill 
. I'd be interested in sizing calculation resources/advice. I don't currently have measurements on pipe length or baseboard length in each of the two zones. The house is two stories and around 2500 sq. ft. (one 6ft. baseboard in the unfinished 1100 sq. ft. basement). Old, single-pane, wood double-hung windows with single-pane storm windows.
As little as I want to mess with it, I'd still like to get this burner firing correctly if I'm going to keep it for at least another year.
Attached is the nameplate.
. I'd be interested in sizing calculation resources/advice. I don't currently have measurements on pipe length or baseboard length in each of the two zones. The house is two stories and around 2500 sq. ft. (one 6ft. baseboard in the unfinished 1100 sq. ft. basement). Old, single-pane, wood double-hung windows with single-pane storm windows.As little as I want to mess with it, I'd still like to get this burner firing correctly if I'm going to keep it for at least another year.
Attached is the nameplate.
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Then namplate says 160,000-out /200,000-in = 80% steady state combustion efficiency.
At typical 2500' 2x4 framed house with R11-R13 fiberglass in the walls and R20-ish attic insulation and clear glass storms over wood sash single panes typically comes in at about 45-50,000 BTU/hr @ 0F if it has no foundation insulation,, 35-40,000 BTU/hr @0F if the foundation is insulated. The coldest locations in Iowa have a 99% outside design temp of about -10F, which means even 60,000BTU/hr of output would most likely have you covered, even without an insulated foundation/band-joist.
You don't need anything like 100K unless your walls leak as much air as fly swatters, and at a 160K of output it would probably keep up with several windows open even during sub-zero weather.
Being something like 3-4x oversized for the load means it wouldn't get better than 70-75% as-used AFUE efficiency even if it were brand new and actually had a flue damper (standard equipment on new boilers.) Without the flue damper you're probably looking at 65% AFUE if the thing were in "like new" condition, but probably 60% or lower given it's antiquity. Replacing it with a right-sized (or no more than 1.7x oversized) 83-85% efficency boiler would probably cut fuel use by at least 35%, and replacing it with a right sized condensing boiler maybe 50%.
The burners are build with little nozzles/jets on the manifold that inject gas in to the long tubes, that also have adjustable air intake, visible in picture #3. It's likely that the disfunctional burner's jet is clogged with either corrosion or crud (sometimes even tiny spider set up shop in them over the summer.) With both the power and the gas valve shut off the boiler you might see if you can't unscrew the jet from the manifold without ripping it all apart. Use the right sized non-wrench, not an adjustable.) The connection to the long burner tube is usually not a firm attachement- the tube simply slips off if you can get enough wiggle room. You may have to pull the manifold out wholly out to get at it, in which case you can probably clean up the jet without removing it from the manifold. When working on gas plumbing you need to use pipe-dope when re-fitting them, and it may even be technically illegal to do as a DIY unless you have a gas fitters license (as is the case in many states.)
It's always better to size the boiler to the load rather than to the radiation, but the lengths of the baseboard (on each zone) often affects the boiler choices. For 160,000 BTU/hr of boiler output to balance with the radiation takes over 250' of baseboard. Any less than that and it will cycle the burner during calls for heat. If you in fact have that much baseboard you would be able to take great advantage of condensing gas burners. If you don't have that much, it's critically important to limit the maximum size of the boiler to what the baseboard can actually deliver. But that's a limit, not an optimal size. The optimal size (per ASHRAE) is 1.4x the heat load at the 99% outside design temp, though it'll still meet it's nameplate AFUE numbers at 1.7x oversizing. Putting that into some perspective, assuming a 99% outside design temp of -5F, at 1.4x oversizing you'd be good down to -40F or cooler before it actually loses ground and can't keep up.
If you picked a new cast-iron boiler that was right sized for your load and put it out for competitive bid you can probably get it installed for $5-6K all-in, including a new system pump and a right-sized flue liner sized for the smaller boiler. For another grand you could get an indirect fired hot water heater to run as a separate zone, which would improve overall AFUE by giving the boiler a higher duty-cycle. Condensing boilers could be twice that, sometimes more, depending on the system particulars.
At typical 2500' 2x4 framed house with R11-R13 fiberglass in the walls and R20-ish attic insulation and clear glass storms over wood sash single panes typically comes in at about 45-50,000 BTU/hr @ 0F if it has no foundation insulation,, 35-40,000 BTU/hr @0F if the foundation is insulated. The coldest locations in Iowa have a 99% outside design temp of about -10F, which means even 60,000BTU/hr of output would most likely have you covered, even without an insulated foundation/band-joist.
You don't need anything like 100K unless your walls leak as much air as fly swatters, and at a 160K of output it would probably keep up with several windows open even during sub-zero weather.
Being something like 3-4x oversized for the load means it wouldn't get better than 70-75% as-used AFUE efficiency even if it were brand new and actually had a flue damper (standard equipment on new boilers.) Without the flue damper you're probably looking at 65% AFUE if the thing were in "like new" condition, but probably 60% or lower given it's antiquity. Replacing it with a right-sized (or no more than 1.7x oversized) 83-85% efficency boiler would probably cut fuel use by at least 35%, and replacing it with a right sized condensing boiler maybe 50%.
The burners are build with little nozzles/jets on the manifold that inject gas in to the long tubes, that also have adjustable air intake, visible in picture #3. It's likely that the disfunctional burner's jet is clogged with either corrosion or crud (sometimes even tiny spider set up shop in them over the summer.) With both the power and the gas valve shut off the boiler you might see if you can't unscrew the jet from the manifold without ripping it all apart. Use the right sized non-wrench, not an adjustable.) The connection to the long burner tube is usually not a firm attachement- the tube simply slips off if you can get enough wiggle room. You may have to pull the manifold out wholly out to get at it, in which case you can probably clean up the jet without removing it from the manifold. When working on gas plumbing you need to use pipe-dope when re-fitting them, and it may even be technically illegal to do as a DIY unless you have a gas fitters license (as is the case in many states.)
It's always better to size the boiler to the load rather than to the radiation, but the lengths of the baseboard (on each zone) often affects the boiler choices. For 160,000 BTU/hr of boiler output to balance with the radiation takes over 250' of baseboard. Any less than that and it will cycle the burner during calls for heat. If you in fact have that much baseboard you would be able to take great advantage of condensing gas burners. If you don't have that much, it's critically important to limit the maximum size of the boiler to what the baseboard can actually deliver. But that's a limit, not an optimal size. The optimal size (per ASHRAE) is 1.4x the heat load at the 99% outside design temp, though it'll still meet it's nameplate AFUE numbers at 1.7x oversizing. Putting that into some perspective, assuming a 99% outside design temp of -5F, at 1.4x oversizing you'd be good down to -40F or cooler before it actually loses ground and can't keep up.
If you picked a new cast-iron boiler that was right sized for your load and put it out for competitive bid you can probably get it installed for $5-6K all-in, including a new system pump and a right-sized flue liner sized for the smaller boiler. For another grand you could get an indirect fired hot water heater to run as a separate zone, which would improve overall AFUE by giving the boiler a higher duty-cycle. Condensing boilers could be twice that, sometimes more, depending on the system particulars.
