Letter 15077

Outdoor wood furnaces : Stainless vs mild steel boilers [New York] 

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We are looking at outdoor wood burning furnaces. We where told there are certain elements if in your water they can corrode stainless steel. Some of these boilers are made with stainless steel. Should we go with mild steel over stainless or is this a dealers ploy for us not to buy stainless. Please give us an answer asap because we need to get something installed right away.

Thank you,

Mary S [last name deleted for privacy due to age of posting]
- Mooers, New York, USA

I HAVE SEEN MILD STEEL UNITS, SIXTEEN YEARS OLD. UNDERSTANDING THE PHYSICS OF WHAT CAUSES CORROSION IN THESE TYPES OF METAL IS KEY. WATER ABOVE 175 DEGREES DOES NOT HAVE AVAILABLE OX. FOR CORROSION. MOST OF THESE UNITS RUN AT 180 - 185 DEGREES. 304 STAINLESS IS EXTREMELY PRONE TO STRESS CORROSION CRACKING - WHICH RESULTS FROM CHLORIDES IN THE WATER REACTING WITH THE NICKEL CONTENT OF THE STEEL. THIS IS NON-REPAIRABLE BY WELDING. 409 STAINLESS WILL GIVE YOU THE HEAT TRANSFER ABILITIES AND EXPANSION PROPERTIES OF MILD STEEL, IT IS A FERRITIC STAINLESS, SO THE SURFACE WILL TARNISH. THE CORROSION RESISTANCE IS STILL GREATER THAN MILD STEEL. THE CLASSIC FROM CENTRAL BOILER AS MENTIONED ABOVE HAS THE MOST EFFECTIVE DESIGN WITH THE FEWEST PARTS. KEEP IT SIMPLE.

JERRY SOBOCINSKI
- MEMPHIS, MI, USA

Definitely go with the mild steel when you buy an outdoor wood furnace. I've seen both in use and the mild steel will not have the corrosion problems that the stainless steel has. I currently own a WoodMaster with mild steel and I can give my testimony that it has worked perfectly and has needed no maintenance or upkeep for any type of problems. I don't speak from a "metallurgy" knowledge, but from practical experience that has done me well.

Bill Kurtz
- Fort Wayne, IN, United States

I am searching for an outdoor wood burning furnace. all brands claim to be the best. my question is which is really better? you also here stainless over mild steel. an mild steel over stainless. which should I get? do you prefer closed loop or open loop? so I need some advice ASP.

George R [last name deleted for privacy due to age of posting]
break press oper. - Flat Rock, N.C. , USA

Which is the better truck--Chevy, Dodge, or Ford? Do university professors present history as it was or with a leftist slant? There really are no objective answers to some questions, but I would suggest seeing if Consumer Reports [link is to product info at Amazon] or some similar testing outfit has ratings available for you.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

I feel that I may be able to put a little spin on some of the comments. As you said, check consumer reports, etc. I personally have built 4 outdoor wood stoves, with the oldest being 7 yrs. Theses stoves are all simple to build, and work quite well. You must remember that up here in Canada, we usually get a lot colder than most of the US. What I am trying to say ia that like anything you buy,if you want it to last, treat it right. Do not burn green wood constantly. Do not let it sit all summer with the ashes still in it. Run the temperature higher, it will burn cleaner. Put a taller chimney on it, it will burn better and won't smoke you and your neighbors out. These are all factors which you should consider before deciding to buy a stove. The stoves that I have built are all made from mild steel, but the thickness of materials can also determine life expectancy. I have used 1/4 inch fireboxes on three stoves, with #4 being 5/8 wall x 36 in. dia. pipeline pipe. The smoke pipe that travels through the water jacket is all 1/2 in wall pipe. These stoves will go for a minimum of 10 yrs. with no maintenance. I am going to have some pictures and other info posted at gardengrapevine.com soon. Maybe some of you could build your own stove, and save a ton of money. By the way, I am not an engineer. Just a guy who likes to build stuff.

Thank you,

Dan Hurd
- ThunderBay, Ont, Canada

The Outdoor wood boiler discussion is interesting. The family business was tool and die and metal stamping, I've worked in the maintenance field for over 20 years, I even had my own welding business for a period, I'm presently an electrical systems support specialist...

I look at the quality of the work, and the price (now and down the road). The money savings is generally why one burns wood for heating. The quality and integrity is going to determine the longevity of the wood boiler. Good maintenance and storage in the summer months are very important!

I'm having my wood boiler built by a local fellow (One of the best welder fabricators I've ever seen) for 2,900.00 without the shell and without the other bells and whistles because I'm going to put it in a small room in my shop and then run my lines to the house- heating my hot water, my house and even a setup attached to my clothes dryer (I have seven children- we do a lot of laundry). This fellow built one for another fellow and it works great.

Mark Sill
- Plymouth, IN

Just to set the record straight on stainless steel, it doesn't work in an outdoor use. It can't account for the rapid temperature changes. I am only starting to get into the heating business and I already know that stainless steel is a nice concept but when you have a cracked water jacket and there is know way to fix it, don't come crying to me. Also I love reading about all these companies with there lifetime warranties who have only been in the business for 3-5 years, give me a break. As soon as one claim comes in they go bankrupt and your on your own once again. Mild steel is a metal that works and if you have half a brain to take proper care and daily maintenance of your furnace it will last you. Thanks for your time.

Tim Suderman
- Winkler, MB, Canada

Titanium enhanced stainless steel is the preferred metal.

High nickel stainless expands and contracts too much.

Carbon steel will transfer the heat better than stainless though.

Hope this helps

Dale Andrews
- Dinwiddie, VA, USA

I am looking for an outdoor furnace and researching the web. I found this discussion interesting. I have lived in the country for most of my life and there is one practice that has some implications w.r.t. the question of metal selection and water. That is the use of bleach on occasion to eliminate colliform contamination in drinking water. Bleach is an oxidating agent and will speed up the general corrosion in circulation boilers and water heaters. You may want to consider glycol and an exchanger. In any event, if you have to treat your drinking water and are using bleach to do so, expect it to have a periodic negative effect on metal surfaces it comes in contact with.

Doug McPhee
- Cranbrook, BC, Canada

I found this interesting. Looking at various stoves the companies that don't have stainless steel say it cracks and mild steel is better. The ones that do say it avoids corrosion better than mild steel. I personally would go with the stainless because I haven't seen much proof of the stainless cracking at wood burning temperature. I was told it would have to be much warmer and it won't get that hot with water around the firebox.

Andy Staupe
- Foxboro, WI

We own a stainless model and after 5 years the 10 year warranty was a joke just try to collect. its a discarded junk heap is it the stainless I have been welding lots of steel stoves for pitting but never seen one crack .

Clayton Brinkman
- Kenora, Ontario, Canada

We have been in the business of outdoor units for many years. We sell all three, mild steel, 409 stainless and 304 dairy grade stainless. Yes, they will all do the same job for a while. No, I have never seen 304 grade crack. Mild steel is the cheapest and 304 is the most expensive. 409 is middle of the road. There is a reason for that. If you are serious about your decision, go to a neighbor that has a mild steel unit and get a water sample from their stove, yuk. Then go to your other neighbor with the 304 and get a sample. You will see the difference. In my years of experience, like one other said, buy the best stainless you can afford. If you are choosing mild steel because that is all you can afford, take out a partial loan and get stainless. As for 304 cracking, that is horse sh*t. We have hundreds of units in 304 grade working perfectly. You must remember that this is not a cremator, it is an outdoor wood furnace with 180 degree water surrounding it. I have sold, installed and serviced many hundred units and plain mild steel will never be a more cost effective decision in my book. Cheaper up front yes, better overall value, not a chance. KISS keep it stainless steel.
Stay warm my friends. `

Douglas Weed
- Lafarge WI, USA

TRY THIS.FOR THOSE OF YOU THAT WANT TO BUILD YOUR OWN. HERE IS WHAT I DID. I WENT TO A METAL SCRAP YARD AND BOUGHT FOR 10 CENT A POUND A PAIR OF ROLLERS OUT OF A PAPER MACHINE. A LOT OF SCRAP YARDS HAVE THESE SINCE THE PAPER INDUSTRY IS NOW IN MEXICO OR ELSEWHERE. A PAPER MACHINE HAS 8 TO 16 ROLLERS IN IT FROM 18" TO 48". I BOUGHT A 48"L X 48"W AND A 48"L X 36"W. BOTH HAVE .500" THICK CHROME PLATED FACED WALLS. ONCE I (CAREFULLY)TOURCHED OUT ONE END OF THE 48" ROLLER AND TRIMMED THE SHAFT I (ALSO CAREFULLY) SHORTENED THE OTHER TO 40" BY TOURCHING OUT THE INSERT AND SHORTENED THE TUBE, THEN REINSERTED THE INSERT AND WELDED. THESE ROLLERS ARE PLUS OR MINUS .010 IN SIZE, WHICH IS REAL NICE TO WORK WITH. AFTER WELDING TANK IN TANK I CUT OUT A 30 X 30 DOOR AND FRAMED IT WITH .500 PLATE STEEL. DOOR IS MADE OF .500 PLATE AND 1" INSIDE DIMENSION .375 CHANNEL STEEL FOR THE FRAME SIDES. 1" FIRE SEAL ROPE IS INSERTED IN THE DOOR GROOVE AND IS ADJUSTABLE ALL 6 WAYS BY SHIMS. WITH .500 STEEL, ADJUSTMENT HAS NOT BEEN NEEDED. I GOT A FUEL OIL BURNER FROM A 150000 BTU FURNACE AND USE IT AS THE FORCED AIR FOR THE WOOD FIRE ON A 185 TO 165 STAT. I ALSO BUILT IN A DUAL FUEL BACKUP BY WHICH WHEN THE SECONDARY STAT HITS 155 THE PUMP AND IGNITER FIRE FOR FUEL OIL HEAT. THE FUEL OIL TANK IS BUILT IN UNDER THE WATER JACKET. AT 185 THE FUEL OIL CUTS OUT TILL THE NEXT FIRING. I MODELED THIS FURNACE AFTER THE WOODMASTER 4400 SINCE I WAS TOLD IT WAS THE MOST EFFICIENT IN THE INDUSTRY, INCLUDING THE HEAT FIREBOX PIPES AND THE SMOKE BYPASS DOOR. THE UNIT HOLDS 300 GALLONS OF WATER AND HAS BURN TIMES OF 24 TO 28 HOURS IN WINTER +20 AND 18 TO 22 FROM 0 TO -10. I HEAT A 1600 SQ FT HOUSE AND HOT TUB AND INTERMITTENTLY A 32 X 40 POLEBARN WHEN NEEDED. I BUILT MY OWN TWIN SIDEARM HEAT EXCHANGERS WITH 2" COPPER AND .750 COPPER INSIDE FOR A 60 GALLON WATER HEATER. I PLUMBED MY HOUSE FOR HYDRONIC BASEBOARD HEAT WITH 6 ZONES AND HAVE IN TOTAL AROUND 3800.00 IN ALL OF IT. I WAS PAYING 185.00 A MONTH IN PROPANE AND ABOUT 600.00 + - PER YEAR FOR ELECTRIC FOR THE HOT TUB WE USE DAILY.

I HAVE THOUGHT ABOUT BUILDING THESE COMMERCIALLY BUT I DIDN'T TRUST THE THINGS I WAS READING ON THE INTERNET SO I DON'T THINK ANYONE WOULD BELIEVE WHAT I WAS SAYING AFTER I WENT INTO BUSINESS. SO I WILL JUST DRIVE MY SEMI WHICH IS WHAT I DO 10 HOURS A DAY.

Bran Thomas
- Kalamazoo, MI, USA

Stainless or mild steel...I have seen both leak in less than 3 years and I have seen both last longer...they are all built cheaply....come on...fire boxes 3/16 and water jackets as thin as 1/8 inch!..warranties that fall apart faster than the stoves...I have personally seen one rot a hole in less than 3 years and the "rock solid 20 year pro rated warranty" was a free patch of 1/8 rolled plate that the guy had to pay me to weld on at his expense!

stainless fire boxes on all models i have seen still have plain steel water jackets (so steel has to meet stainless somewhere) where is the advantage of stainless?

William Gordon
- Watford, Ontario, Canada

Chris I am no expert on these things (as I am sure some one else will likely point out,,lol) and I have never seen any of those "gasification " models in my area yet...I have seen numerous of the other kind in operation...as for their durability it does seem to have a lot to do with the owner (although I personally think they are built way to thin) and the ones I have seen rot out early tend to sit outside in the elements and are surrounded by a steel siding of some sort...here I think lies much of the problem...the driving wind pushes snow through the tiny crevices in the steel siding...this snow collects on the water jacket...melts..runs to the bottom of the stove and is trapped in the insulation....rust out prematurely (again my opinion, but I now have welded 2 stoves in the same spot)

The ones I have seen are not as efficient as the sellers claim to be....I was told I could not build one as good...I did build my own...and in comparison to others in my area..it is just as efficient (although I am certain they can be improved on)..i heat a home of about 2,200 sq ft. a small 30 x 40 shed (at lower temps that the house) and my hot water, I use between 8 and 10 bush cords of wood (when I had an indoor wood furnace I used about half that..but I was not heating any hot water then either, or the shed) I do believe it is not as efficient but I traded that for no more smoke or ashes or open fires in the house..I think you will burn a lot of wood to heat the area you are speaking of...but my wife likes to keep the house over 70

I light my stove in October and usually run it till the first of June anywhere from 1 fill per day to twice daily in the heart of winter

If you are serious about a stove...check all the ones you can find..ask not jsut a dealer...maybe write a manufacturer and tell them how big an area you are going to heat....then when you have done all that... do as I did...build it heavier yourself...
these things are built like any appliance..to where out so they can sell you a new one

like I started out saying...just my opinions..i am sure you will hear many more.

William Gordon
- Watford, Ontario, Canada

I have owned a stainless stove 9 years and after 5 years it was cracked like spider web waranty covered a new water jacket I paid $600 to ship old and new units and did all the work myself they said cracking was due to salt in the water and i should use only rain water ok!?? 4 years later the stove is cracked and leaking again! stainless is junk that will not hold up stress of heat cool cycles of these boilers mild steel can be repaired by any good welder a friend got a central boiler unit mild steel half the cost burns less wood and going strong i will be installing a new indoor wood boiler the outdoor units are too hard on the wood supply and no stainless steel on the wood stove

Duane Ingalls
- clymer new york USA