cast iron or steel boiler?

Well Ive ben lurking around the site for a while along with some wood burnings sites and I think i've decided to go with a combo wood/coal boiler. My conclusion comes from hours of searching and learning and because I can usually get some wood for free but not all I want the option of burning both realizing I will loose some conveinence and effiecency.
So I'm looking at the harmon sf230 , attack fd , eko coal. I spoke with dealer for the attack fd and the eko and he was very hesitant with cast iron boilers and reccommended the attack dp that is a gasification wood boiler that you can burn wood/with coal. He said it is very difficult to control the cast iron boilers. So I would appreciate any coments on fuel usage and comparisons

I don't think cast iron has a thing to do with control. Control is in the design and manufacture. Generally, cast iron lasts longer. If you made two identical units, one steel. one cast, about the only difference you'd notice is the cast iron would take longer to heat up & longer to cool down. Cast is more corrosive resistant.

I don't think you will see many cast iron coal/wood boilers out there. Generally the pressure vessel is made from steel and the doors are cast iron. It really doesn't matter what material is used, it would be the design that determines how well it would run.

That said, does anyone even make a cast iron coal boiler today? I would think the production numbers would have to be pretty large to make it worth the investment to produce a cast boiler.

The cast models I researched were euro made Buderus, ECO, Attack and are availible thru new horizon online. There footprint and chamber seem smaller. If anyone is using them or a harmon sf230 please any comment would be helpfull

Personally I'd go with a Harman hand fired boiler. I know they will burn coal well and also burn wood.. I don't know enough about the others to comment, except to say that most units that claim to be wood and coal burners are usually wood burners that can burn coal only marginally well.

Take a look at the several threads on the Clayton, US Stove, Hot Blast, and other wood/coal combo units.. most people have a lot of frustration getting these wood burners to burn coal well.. the best is probably the Clayton,, the firebox design is closest to an ideal coal burning design.

You need a good chimney to provide a reliable draft to a hand feed boiler, this is critical, and a Barometric damper to control the draft.

Hope this helps,
Greg L

dperg wrote:The cast models I researched were euro made Buderus, ECO, Attack and are availible thru new horizon online. There footprint and chamber seem smaller. If anyone is using them or a harmon sf230 please any comment would be helpfull

To be honest, I would stay away from cast if I could. It may be the ideal material, but it is a nightmare to repair and adds to the price. Buy a reputable US appliance in steel and spend your savings on coal is my advice.

Cast iron is the best material for a boiler.That being said the thickness of the coal boilers steel is so thick that they will most likely last a lifetime or more.I think the best boiler would be the one you can get parts for 20 or 30 years down the road.
DON

Cast is not, in my opinion the best material.. the problem is that cast iron must be cast in managable sections, then the sections plumbed and sealed and bolted together,, this creates many locations for leaks and expansion/contraction issues.. Cast is prone to cracking from thermal shock.

It's hard to argue with my AA260, it was in a house next to the Susquehanna River, the boiler was under water several times. The boiler NEVER got any maintenance, except to bandaid it enough to get it running again. The boiler is stamped with the production date: 1950. With zero preventive maintenace, this all steel boiler is in amazing shape. The inside appears to be only a year or two old.. I expected to have lots of corrosion, but only surface rust on the inside of the water jacket.

If the house that my boiler came from had a cast iron sectional boiler in it, it would not have lasted 50 years in that location..

Greg L

Now that I've been reading "coal" for 6 months, I think I should have said "burning oil, cast lasts longer". With oil boilers steel boilers last about 15 yrs and cast iron "last forever", BUT, I've read of amazing life from steel coal boilers and certainly steel has some good advantages. Thermal shock doesn't bother steel enough to worry about and steel can easily be repaired if need be. As Greg mentioned, the steel used in coal boilers is so darn thick it makes the life incredibly long.

The debate between cast iron and steel could last until the end of time. Both have desirable properties depending on the situation.

I think the trick to keeping steel from corroding is two fold: a tight closed system and water treatment. It is an area no one seems to deal with much. When I was looking into it, no local boiler techs used water treatment of any kind and looked at me with a funny stare when I brought up the subject. The local supply house had nothing in stock for closed systems. Why should they care? It only prolongs the life of the boiler! Those guys are no where near the scene of the crime when the leaks are detected seven or so years down the road. No one blames the technician that far in the future, though they should!

There is little information on it on the web. I used an Air Force and an ASHRAE guidance paper on water treatment. If done correctly it will keep the boiler from corroding. I used softened water treated with sodium nitrite, borax, and washing soda. It was the simplest/cheapest to obtain and least likely method for me to screw up.

http://www.afcesa.af.mil/shared/media/d ... 13-040.pdf

1. Nitrite-Borax Treatment Program
a. For the initial dosage, add approximately 18 lbs of sodium nitrite-borax for
every 1000 gallons of water in the system. Enough sodium nitrite-borax should be added to
sustain a nitrite residual of 1000 ppm as nitrite (NO2).
b. Maintain a nitrite residual of 600 to 1000 ppm.
c. Add sodium carbonate to maintain the pH at 8.5 to 9.5.
d. Check pH and analyze the system water to determine the nitrite content 24
hours after initiating treatment.
e. Make necessary adjustments, if needed.

No one locally had a stock mixture so I found the US Army boiler treatment program had proportions by weight: 68% Sodium nitrite, 10% Borax, 17% soda ash, 5% copper corrosion inhibitor. I left out the last ingredient since I had no idea what it was specifically and the Air Force program didn't mention it. If anyone knows what it is, let me know please!

ASHRAE indicated it was better to err on the over saturation side, so I did. It is critical that the pH remain between 8.5 and 9.5 for it to work effectively. I believe that the theory is that it actually forms a film on surfaces by controlled oxidation. Once filmed over (with magnetite), the surface oxidation stops. I could be wrong on this. The engineers on this site will correct me as needed-hopefully!

Does anyone here treat their boiler water or monitor pH?

Weil McLain cast iron boilers are suggested to have water adjusted to a a ph of 7.0-8.5 See:
http://www.weil-mclain.com/professional ... SB0103.pdf

I really should check and adjust mine, my well water ph is 5.7!

Yeah, it's time to check my system again too. You have very acidic water, my god!

I believe that weil mclain info was for untreated water. The pH for a nitrite-borax system must remain higher, in the 8.5-9.5 range.

Do you treat your water? Many people don't. Most of the info I read online seemed to be for quite large systems but the military info did indicate treatments for residential systems under 250 degF. I was worried about the mild steel of the 130-m without treatment.

I did make a repair to my primary loop and put in a flo check valve at the same time. I I was able to inspect the piping and all seemed ok at the point of repair; no pitting, thin black film. Then I added some more nitrite borax. The catch to treating your water with nitrite-borax though is that you must keep the concentration above a certain level and the pH at 8.5 to 9.5 otherwise corrosion could be accelerated by the nitrite.