The Steel within our boilers is key to performance.  Many producers of boilers use a type alloy steel called 409, but is it all it’s cracked up to be?

If 409 stainless steel is not annealed or heat-treated in the weld zone in a boiler application, such as a wood boiler or coal boiler, it can lead to several issues:

Loss of Corrosion Resistance

1. Weld Decay: The weld zone can become susceptible to corrosion, particularly in the presence of water and oxygen.
2. Intergranular Corrosion: The lack of heat treatment can cause the formation of chromium carbides, leading to intergranular corrosion.

Reduced Mechanical Properties

1. Brittleness: The weld zone can become brittle, increasing the risk of cracking or failure under thermal stress.
2. Reduced Ductility: The lack of heat treatment can reduce the ductility of the weld zone, making it more prone to cracking.

Increased Risk of Failure

1. Weld Cracking: The combination of thermal stress, corrosion, and brittleness can lead to weld cracking.
2. Boiler Failure: In severe cases, the failure of the weld zone can lead to a catastrophic boiler failure, resulting in costly repairs, downtime, and potential safety risks.

Importance of Annealing or Heat Treatment

1. Restores Corrosion Resistance: Annealing or heat treatment can restore the corrosion resistance of the weld zone.
2. Relieves Residual Stresses: Heat treatment can relieve residual stresses, reducing the risk of weld cracking.
3. Improves Mechanical Properties: Annealing or heat treatment can improve the mechanical properties of the weld zone, including ductility and toughness

So, What is Intergranular Corrosion?

Well, Stainless Steel, like many other metals and alloys, is composed of a crystallite structure.
This means the metal itself is composed of grains of various sizes. Where these grains meet are called the grain boundaries.
Also known as weld decay, intergranular corrosion attacks these boundaries, causing damage to the metal at a molecular
level.

Cracking and grain loss can occur, leading to reduced structural integrity, ability to withstand pressure, and further encouraging
additional corrosion.

The standard Type 409 alloy (UNS S40900) composition does not provide freedom from sensitization of weld heat-affected
zones or base metal following certain thermal exposures.
Indusy reported field failures of welded automotive exhaust system components and other non-automotive fabrications
such as as-welded heat exchanger tubing, have occured on Type 409 alloy even though it met the ASTM stabilization requirement
of Ti = 6x carbon, minimum.

The failures were caused by intergranular corrosion of weld heat-affected zones.

In summary, failing to anneal or heat-treat 409 stainless steel in the weld zone can lead to a range of issues, including loss of corrosion resistance, reduced mechanical properties, and increased risk of failure. 

At Portage and Main Boilers, we use 1/4” W44 cold rolled steel for the firepot and inside water jacket. W44 cold rolled steel is very well known for being uniform, easy to shear and break, and welder friendly. Cold rolled steel (CR) is up to 20% stronger than the hot rolled variety.

The best outdoor wood boiler is a matter of consideration for several factors.

KEY FACTORS TO CONSIDER:
Efficiency
Look for boilers with high efficiency ratings, typically 80% to 85% for standard models and 90% to 95% for high-efficiency, dual-stage wood furnaces.

Size
Choose a boiler that matches your heating needs, considering factors like climate zone, house size, and insulation. A general rule of thumb is 40 to 60 BTUs per square foot.

Cost
Initial costs can range from $5,000 to $7,000, with additional expenses for installation, piping, and maintenance.

Quality
Opt for boilers made from high-quality materials, with a focus on durability and longevity. The average lifespan of an outdoor wood furnace is 15 to 25 years.

Top Recommendation:

Portage and Main Boilers

The Portage and Main Boiler is a highly recommended option, known for its reliability, efficiency, and durability. It features a unique design that maximizes heat transfer and minimizes heat loss, with a boiler efficiency rating of up to 99.

Legend

1st : First pass
2nd : Second pass
3rd : Third pass
4th : Fourth pass
A. Refractory brick lining & dry base design
B. Air from above & below
C. Full length quad-pass heat exchanger and upper baffle
D. Water – cooled rear baffle
E. Sectional, easy to repair design

A. Refractory Brick Lining

The Portage & Main Ultimizer is a refractory lined, dry base boiler. In the industry it has become known as an “updraft gasifier” because of its efficient burn. The Ultimizer is simple to use, easy to maintain and not fussy about the fuel it burns. It is very important to understand the “fire triangle” in order to fully appreciate the advantages of the Ultimizer design, and how it will save you fuel, money and time. To achieve a clean, efficient burn with complete combustion, an optimal balance of OXYGEN, HEAT & FUEL is required. The Portage & Main Ultimizer has been specifically designed to achieve this optimal balance.

Dry base design, zero ash line corrosion & no bridging 
The heat stored in the refractory lining helps ensure that a more complete combustion process occurs. I.e. fuel is reduced to charcoal in a 3-stage process.

STAGE 1: The fuel is heated to evaporate and drive out moisture. This starts at 212 degrees F

STAGE 2: It starts to break down on a chemical level at 500 degrees F. Volatile matter is vaporized. These vapors contain 50% to 60% of the heat value of the fuel, making it imperative for them to be burnt properly at a temperature in the range 1100 degrees F for maximum combustion efficiency. When all the volatile gases have been released, the remaining material is charcoal

STAGE 3: Charcoal burns at temperatures in excess of 1100 degrees F. Latent heat also helps in the re-ignition of the fire at the start of the next burn cycle. It also helps to dissipate moisture that is a result of the combustion process. The dry base boiler design gives a very hot burn. The water jacket sits above the brick line so it isn’t up against the fire, taking away the heat prematurely. This eliminates ash line corrosion and the fuel is completely burnt, resulting in considerably less ash.

B. Air from above & below

Exhaust gases make their 1st and 2nd pass at the top of the firebox where they move under and around a water-cooled baffle and into the heat exchanger. Gases then travel to the front of the boiler in a 3rd pass, make a 180 degree turn and move in a 4th pass to the back of the heat exchanger. In this way, all available heat is taken from exhaust gases before they exit the chimney. It gives up to 50% more heat transfer compared to other non water-cooled, non brick lined designs.

C. Full length quad-pass heat exchanger and upper baffle

The Ultimizer heat exchanger runs the full length of the boiler. It is completely surrounded by water which gives maximum heat transfer

D. Water-cooled rear baffle

The water-cooled baffle at the rear of the Ultimizer fire pot absorbs heat and traps combustion vapors. Turbulence is created when air is introduced from below and above the fire. This turbulence provides an optimal burning environment for the vapors, leading to a hotter and more efficient burn. Also, by trapping the vapors, they are thoroughly burnt before entering the high efficiency heat exchanger. This heat exchanger is totally surrounded by water for maximum heat transfer.

E. Sectional, easy to repair design

Not a throwaway design like other brands are. The Ultimizer weighs substantially more than other brand boilers. That’s due to the heavy weight, long lasting, quality materials that go into our design. It provides a long-term, sustainable solution to your heating needs. At the end of its long life, the water jacket can be replaced. Just remove the top half of the boiler and bolt on a new top section, no welding required and your trusty boiler is good to go again. This means a very sustainable warranty, resulting in savings for the customer of several thousand dollars by rebuilding rather than replacing the entire boiler.

Q. My current outdoor boiler had constant issues with the water jacket, how expensive is it to repair this unit?

The water jacket comes up a lot with customers who’ve used a water boiler before as this is the most frequent point of failure on boilers. Water jackets frequently fail because of ash-line corrosion – our dry-base design has eliminated this. Further to this, ¼” thick cold-rolled steel is used to make the firebox; 2x as heavy as what some competitors use.

Most outdoor boilers are built around this water jacket in such a way that repairing is usually not offered as a warranty solution. Issues requires full dismantling of the boiler and shipping out, or waiting for someone experienced in welding and water jacket repairs to get to you. Both “solutions” often result in days of lost heating. Most warranties will mean a complete replacement of the whole unit.

At Portage & Main, our equipment is built to last, not to be tossed in the junkyard. Should problems with the water jacket arise, it has been built as a separate component within the unit’s sectional design. Simply unbolt and replace or repair on-site within just a few hours. This repair would be 1/3 – ¼ of the cost of competitors.

Furthermore, as EPA standards and levels change, it is nice to know you have rebuildable unit that you can keep, repair and next generations can use far into their futures.

Q. Is the cost of an outdoor wood boiler of this size and style really worth it?

Trying to determine whether the upfront cost of a wood boiler of the size and quality of the Portage & Main Wood Series Ultimizer is worth it will depend a lot upon the household itself and lifestyle factors. We believe the biggest point of worth is that this system offers a reliable degree of energy independence and sustainability for both residential and commercial use. For those living on farms, acreages, or off-grid locations and businesses, a wood boiler is a reliable heating solution. Even when one has access to utilities, having your own outdoor wood boiler means you don’t have to worry about the rising costs of utilities or potential disruptions from storms or other events. Rather, you get to enjoy reliable, sustainable heating by your own design and that’s a long-term benefit that many find well worth the upfront purchase and installation cost. This gives peace of mind, knowing you can run off the smallest most fuel-efficient generator.

And we do mean sustainable. In a recent interview regarding how to be greener at home, executive director of the Massachusetts Forest Alliance Chris Egan explained that while oil and gas boilers have gotten cheaper, the big benefits remain with wood boilers, stating, “you’re reducing your carbon impact and you’re saving money with a wood system.” It’s the only fuel you can harvest yourself, from your own land in many cases. It’s carbon neutral: the sun and carbon grew the tree, the carbon is released when burned, giving back to future forest growth.

Q. This is my first outdoor wood boiler, how hard is it to care for ?

The Portage & Main Ultimizer Wood Series was built to be exceptionally easy to use and maintain.

• The control panel at the back is easy to navigate with quality components that, should they ever need to be replaced, can be readily bought around town.
• The clean-out chamber is designed for easy disposal of ash that’s dropped through the grating.
• The heat exchanger is easy to clean as build-up is minuscule due to the smoke burn in the upper chamber of the firebox. You pull the small amount of soot forward, then push it back into the firebox – keeping all the mess inside the unit.
• The water float system readily and quickly identifies your water levels.

The whole unit has been thoughtfully designed to be approachable and easy to use and maintain, while likewise ensuring durability throughout all the winters it’s in use.

Transform Your Heating with the Portage & Main Ultimizer Wood Series. Are you ready to see the difference our product can offer? Contact the team at Heat Smart Plus today to learn more about the best outdoor boiler for heating homes and farms and how you can get one installed on your property!