New boiler with limitations...

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Old 02-23-11, 06:05 PM
J
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New boiler with limitations...

Hello everyone-I am new to this forum. Here's my situation. I need to replace my 29 year old Burnham RS-112 (125k btu nozzled to 75 k) because of a crack in the firebox. Prices for replacing just the box obviously warrant a new boiler. I need to use a tankless coil because of space restrictions and also because the utility room in which it is located in is an inside room. No way to thru vent and no room for an indirect. I plan on using another Burnham steel dry base,the RSA-125 because it's compatible to the 112 (heat exchanger=14 gals.- 3 gpm coil) and also cut back to a .75 nozzle. I know there are better choices (e.g.cast iron,tankless propane wall units etc) but I'm on a fixed income and limited to cash flow. Ialso know I can put another steel unit(e.g. NY, Columbia, Thermo-Dynamics, Axeman Anderson etc.) but I feel that because I had such Good Luck with the Burnham I'll stick with it. The one thing that concerns me is all the problems I've read about referring to there new style firebox, which according to the I&O manuals, is now that of the NY apu series which they own also. And I've read that they've had problems with theirs to. So I was wondering seeing that most of what I read about the box failures all point to the " joint" between the firebox and the heat exchanger, while it's apart (it's will be a KD unit) is there an upgrade product that's available that I could use in place of the factory material that will increase the longevity of the boiler? Thanks.
Rick
 
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Old 02-23-11, 07:13 PM
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Put the boiler on top of the indirect. The indirect is horizontal and is 24" tall

http://www.crownboiler.com/products/...s/MegaStor.pdf

And get a rear vent boiler like this. So you can get the height.

http://www.crownboiler.com/products/...ODV%202010.pdf

All together you will have 50" height but with the same ft print. probably save on oil too. Thats good if on a fixed income. "Oil aint gettin any cheaper"



Mike NJ
 
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Old 02-24-11, 05:33 AM
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Rsa - retro fit..

Thanks Mike,
Already looked into the Crown also the Energy Kinetics EK over the top model - I don't have the room for the rear venting with the Crown or it's comparible cousin by Burnham (forget the model #) and the EK is way to high (75") I did not mention there is a dryer and washer in the room as well as a well tank. The reason I'm limited to width, and length including burner attached. Have to leave room to remove other appliances. I really would like to go with a Navien propane wall unit(can use chimney for intake and exhaust) but the price is to much and 25 years ago we had a propane hot water tank and almost had a fire secondary to a leak. My wife doesn't even want to hear the word "Gas"(she was home alone at the time) So this is why I am somewhat restricted to a steel dry base. Just need to know if there is a way to improve the seal between the box and exchanger. And having said that, I know a lot of research goes into the design and manufacturing of boilers,but I also know that the technology behind the steel dry base units really haven't changed much, if at all, in many years. So, I ask can I retrofit one of these boilers or just leave it as is and add more insulation where I can and other heat saving repairs(home is 60 year old cape) but has been updated quite a lot over the years. It's slab built using a re-inforced vapor barrier on floor with 2" styrofome insulation(floor very dry - zero moisture) and 2 by 6 ext.walls 1800 sq.ft. which at present uses approx. 650-700 gals./year for heat & hot water. No baseboard on 2nd level and 1st level split 70" and 40" of element with the 1st zone being use the most 2nd zone (40) kept mostly at 55 all the time.
Thanks for any advise.
Rick
 
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Old 02-24-11, 06:05 AM
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How big is the well tank? Can you fit an indirect over the well tank? Your house sounds like it has an interesting layout to be 1800 sq ft and have an interior room with no windows. What's directly above that utility room? No way of routing vents up through the roof somehow?
 
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Old 02-24-11, 08:39 AM
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Rsa

Hello drooplug,
Yes it is an unusual layout - originally a garage. Two additions over the years and of coarse total rehab in original structure. Right above the utility room is a 1/2 bath with a totally full raceway. No more room for plumbing between the waste pipe and dryer pipe. Could probably sneak some romex thru there but that's it. I have a 50 gal. well tank. Stack for boiler 12" above that. Our first addition went over the outside wall for that room, is now partly a hall and a closet.
I know we have limitations!! But it's been a fun challenge over the years. (33) Thanks for responding.
Rick
 
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Old 02-25-11, 05:05 PM
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Whoa Nelly!!! Let's get the horse in front of the cart first. You have a 112 and want to install a 125 and down fire? I hope you enjoy your increased fuel costs.
You need a heat loss and not a measurement of radiation or size off the old boiler, neither of the latter work.
You will be limited but I would think the smallest RSA would work well and save money.
At a .75 input you are already down to 105,000 and I am sure that is too large for 1800 sq ft.
Oversizing the boiler wastes fuel and down sizing is not the answer due to possibility of flue gas condensation.
What type of radiation do you have?
How many zones(thermostats)?
 
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Old 02-25-11, 06:12 PM
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Hell rbeck,
I have 2 zones- the main section has 70' of radiation and the addition has 40'. The addition is kept at 52-55 degrees pretty much all the time. The main zone has 70' and is usually kept at 65( 59 @ night) I use the Lux 500 series progammable therms. The RSA 86 only holds 9 gals. of water - would this not make the burner fire up more because of a quicker cool down when using domestic water? Why would firing down the 125 to .75 use more oil. That unit holds 14 gals. of water. Would this be adding, in one respect, to the thermal mass?
Rick
 
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Old 02-25-11, 06:17 PM
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sorry ire-read your post - I use Slant Fin baseboard. I believe it's the model 30.
Thanks.
 
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Old 02-26-11, 04:21 AM
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If you really have 110 ft of actual finned tube element, the max output of that is around 60,000 to 66,000 BTU/hr. As long as the house heats ok, for space heating there is no reason to go bigger than the RSA85. That is already larger than you need, and should do fine for the domestic coil.

(If the house doesn't heat ok, then you either need to reduce the heat loss by insulating and air sealing, and/or increase the amount of finned element. A bigger boiler won't help -- you're limited by the amount of baseboard. And if you do need more element, tighten the building first. That would indicate a heat loss of at least 33 BTU/hr/sf, which is a really leaky residential building for the construction you describe.)
 
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Old 02-26-11, 05:57 AM
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The problem with downsizing a nozzle creates a few problems.
The biggest is when a boiler is designed there is a ratio of fuel input to the amount of what they call fireside heating surface. This is the metal the hot flue gasses wipe across between the flame and the vent pipe.
If the fire side heating surface is of smaller amount for the firing rate the stack temperatures are higher. If the fireside heating surface is correct we have safe vent temperatures.
When we drop the firing rate we throw the amount of fireside heat exchanger and btu input out of ratio.
Now the stack temperature goes down, possibly into a chimney condensing range which will eventually destroy the chimney. Inside the boiler we reduce thermal transfer even though we have seen an increase in combustion efficiency. Think about this, the flue gasses take the path of least resistance, flue passes without metal contact. This means less flue gasses scrubbing the flue pass walls. When we completely fill the flue passes with flue gasses we will improve the thermal transfer as we completely fill the flue passes forcing more flue gasses against the flue pass walls.
Second point is longer run cycles are better than shorter cycles. The other thing is hot water production is based on btu input to the boiler and water flow (gpm). As a rule of thumb you produce about 1 gallon of hot per 50,000 btu's. So if you have an 84,000 btu boiler fired at .75 gph or 112,000 btu boiler fired at .75 your hot water output is very similar or maybe less. The reason I say less is the smaller firing rate will raise the larger gallons of boiler water slower than the proper firing rate in the smaller boiler water vessel.
I am sure that is clear as mud.
 
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Old 02-26-11, 03:20 PM
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Rsa

Hello rbeck,
Thanks for your feedback I have done a heat loss and come in around 65 k for the boiler. Then the norm(supposedly) is to add 10% for the tankless, which now brings me to around 70k. Presuming a tight house. My home could use some more insul. but in areas that are difficult to get to. But I'm working on it. Now having said that the only diif. between the rsa125 and the 85,beside the nozzle, is the heat exchanger on the 85 has 4.5 less gals. of water, the tubes are the same diameter (1 1/2") and there are 12 of them. The difference is the exghanger is 5" shorter than the 125. My feeling is I'm better off with the increased volume for greater thermal mass, because I chose the steel boiler over a cast iron. Again space restrictions. Also I failed to mention over 800 sq.ft. of the house has 9" ceilings and the living room (280 sq.ft.) has cathedralceilins with skylights,bay window and french ext. door and an 36" glass entrance door(lots of heat loss) I felt the the 85 would be working near max. capacity and thus use more oil and decrease longevity. So now having said what you said about the thermal transfer from the tubes to the mass(water) and seeing the tubes are identical(except for height) Ifelt the best choice is the 125.
Presently my RS -112 is also a 125k rated unit and for years I used a .85/80B nozzle until 3 years ago and then reduced it to a .75/80w and found it to be a bit more effeicient and still gives plenty of hot water. Believe it or not I we have well water and never had to change or backflush the coil and still plenty of hot water. I'm hoping to get the same from the new unit. Any other suggestion or advise is very much appreciated. Thanks.
Rick
 
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Old 02-26-11, 06:57 PM
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Working near the max is what you want to do. Oversizing is inefficient.
 
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Old 02-27-11, 07:30 AM
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Any other suggestion or advise is very much appreciated.
Don't try to 'second guess' engineers and professionals.
 
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