Molten Iron Icon
400,000 BTUs
Product Details




Fuel Type

Natural Gas/Propane

Footprint *

52” x 36” x 22” HWD

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* All dimensions rounded up to the nearest inch
KN 4 Boiler
KN-Series Boilers KN-4 Submittal Data
Technology overview

Standard Features and Benefits

  • 5x more wall thickness than stainless steel and aluminum
  • 90% AHRI Certified Efficiency
  • 25-Year Heat Exchanger Warranty
  • Accepts 10:1 range of water flows (Variable Volume Systems)
  • 100 PSI maximum working pressure
  • Tru-Flow Advanced Air/Fuel Delivery System
  • Assembled boilers use 80% post-consumer recycled materials
  • Plastic components are made from 40% post-consumer recycled materials
  • LEED Qualified
  • Factory Piped & Wired
  • Vent/Intake Runs of up to 80 Equivalent Feet
  • HEATNET Control Platform w/ Touchscreen
  • Optional HEATNET Online Remote Monitoring
  • Natural Gas/LP Gas/Dual Fuel
  • Low NOx & CO2
Cast Iron Heat Exchanger – Durable and Reliable

Why Cast Iron

An ideal material for condensing boiler applications, cast iron is produced using casted metal, making the construction stronger than metals that are welded together. With fewer seams and joints, KN-Series' cast iron heat exchangers can handle more heat and more stress. And with corrosion-resistant properties, cast iron is inherently less sensitive to both acidic and basic pH levels. With the strength, durability and longevity needed for today's most demanding boiler applications, the cast iron technology sets KN-Series condensing boilers apart from the competition.

TRU-FLOW Advanced Gas Train

KN’s advanced gas train design is responsive and completely adaptable. Tru-Flow Fuel/Air Coupling is a unique boiler control system developed to keep KN-Series cast iron boilers running cleanly and efficiently. By constantly monitoring and regulating the flow of both fuel and air, Tru-Flow can achieve an optimal 1:1 fuel mixture and is capable of automatic adjustments if the flow is compromised, ensuring continuous, safe and reliable operations. Working in conjunction with integrated HEATNET 3.0 boiler management system controls, Tru-Flow helps match load conditions with boiler output for optimal energy efficiency.

  • Full burner modulation safely and accurately
  • Burner efficiencies up to 99%
Virtuoso Logo
High Turndown

All KN-Series boilers are available with our NEW Virtuoso₂ high turndown system. Working off the legendary Tru-Flow air/fuel coupling system; the engineers at ATH have developed an air shutter driven system expanding the KN's turndown ratio to 10:1.

O₂ monitoring

Temperatures and air density changes can effect boiler combustion. O₂ sensors measure oxygen levels in the exhaust. The Virtuoso₂ control platform incorporates a proven Bosch O₂ sensor for real-time monitoring that can be instantly accessed by operators and technicians for instant adjustments for improved efficiencies and lower emissions.


Greener Building

In an age where we are obligated to protect the environment for future generations: greener is better. There’s nothing greener than the KN-Series cast iron boilers. There is no other piece of equipment in the world as environmentally friendly as the KN-Series condensing cast iron boilers. As condensing boilers, the KN-Series units are constructed with a durable cast iron heat exchanger, enabling each unit to cycle longer and less frequently, as it retains latent heat longer and requires less energy to bring back to operating temperature. When coupled with the precise digital controls of HEATNET 3.0 boiler control software, KN-Series offer optimum efficiencies through full modulation.

The specially designed cast iron heat exchangers at the core of all KN-Series boilers are manufactured utilizing over 90% post-consumer recycled materials, which makes them completely recyclable! KN-Series condensing boilers are quiet and operate efficiently with low NOx and CO2 levels.


Application Flexibility

In combination with custom-engineered, onboard boiler controls, KN-Series boilers' patented cast iron sections accommodate a wider range of piping and water flow conditions more so than any other material or technology on the market.

All KN-Series condensing boilers are capable of variable volume water flow up to 10:1 range and have low-pressure drops through the cast iron heat exchanger, and are also capable of delta T's of 20-100 with single pump system piping (reverse return) or primary/secondary piping. In direct comparison, competitive units typically have delta T's in the 20-40 range due to high-pressure drops and are not capable of single pump piping.

In addition to carrying a 25-year heat exchanger warranty, KN-Series boilers have virtually no inlet water temperature limitations making them the perfect condensing boiler unit for one of the fastest growing segments in the hydronic heating market: snow melt and radiant heating.

25 Years!


Advanced Thermal Hydronics warrants that the Cast Iron primary heat exchanger (Cast Iron Block) will be free from defects in material or workmanship and against failure due to condensate corrosion, for a period of twenty-five (25) years (non-prorated) from the date of shipment from the factory. This warranty will cover damage due to thermal shock, such as leaks to the cast iron sections, when installed as a closed loop hot water boiler.