Wondering whether stainless steel or mid steel is better in outdoor boilers? Let me try to persuade you. We'll be comparing five points.
1. Heat Tolerance
While .409 stainless can take heat up to 1400ºF, carbon steels used in outdoor boilers begin to break down as soon as temperatures reach 800ºF, limiting the lifetime of mild steel boilers.
2. Corrosion Resistance
While mild steel begins slowly rusting away from day one, stainless steel is coated with a layer of chromium oxide, keeping oxygen from penetrating and causing corrosion.
3. Heat Transfer
.409 stainless steel has the best heat transfer of any stainless steel, having about 60% more heat transfer than .304 stainless steel. When factoring in that stainless steel boilers do not need as thick of steel due to the added corrosion resistance, .409 stainless has a very similar heat transfer capacity to mild steel.
.409 stainless steel is enhanced with titanium, making it the best option for tolerating wear and tear, and expansion and contraction caused by changing temperatures.
5. Thermal Expansion and Warping
Again, 409 Stainless Steel outperforms all other stainless steels used in outdoor furnaces having a very low expansion rate and one that is similar to mild steel. This is why you will see furnaces made out of 304 Stainless Steel warp and spider crack often and be very hard to weld on. This is also why you can see our furnaces withstand a fire or burning low on water while other furnaces cannot.
In the past, many outdoor wood boiler brands attempted to cut costs by making their boilers out of mild steel or boiler plate but after years of boilers being used in the field, they're beginning to embrace stainless steel as it simply lasts longer than other steels.