Dunkirk DXL-K Cast Iron Gas Boiler
High-output atmospheric gas boiler — 10 sizes, 50–300 MBH, hot water and steam configurations, and a 20-year non-prorated cast iron warranty.
Don't "FREEZE" — Call D's...
Boiler Type
Cast Iron Atmospheric Gas Boiler
AFUE Efficiency
84% AFUE
Fuel Type
Natural Gas / Propane
Heat Exchanger
Cast Iron Sections
Application
Residential & Light Commercial
Venting Type
Category I / B-Vent (Chimney)
Installation Type
Floor Standing
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Dunkirk DXL-K — Chicago's Workhorse Boiler
The Dunkirk DXL-K is a heavy-duty cast iron atmospheric gas boiler available in 10 sizes from 50 to 300 MBH. Designed for both hot-water and steam heating applications, it is the go-to replacement boiler for Chicago's two-flats, greystones, and older homes with cast-iron radiator systems.
Built around Dunkirk's proven cast iron section technology, the DXL-K delivers reliable, even heat through atmospheric combustion with titanium composite burners. Its wide capacity range, straightforward controls, and Cast-to-Last 20-Year Non-Prorated Limited Warranty make it one of the most trusted residential boilers in the Chicago market.
Key Features
Cast Iron Heat Exchanger
Heavy-duty cast iron sections with push nipples deliver decades of reliable, even heat transfer and superior corrosion resistance.
Integrated Boiler Control
Factory-installed control module combines temperature limit, circulator relay, and diagnostic indicator lights in a single unit.
20-Year Non-Prorated Warranty
Dunkirk's Cast-to-Last warranty covers the heat exchanger for 20 years, non-prorated — among the strongest residential boiler warranties available.
Atmospheric Combustion
Proven atmospheric burner design with titanium composite burners and automatic redundant gas valve for reliable, low-maintenance operation.
Hot Water & Steam Capable
Available in hot-water and steam configurations — ideal for Chicago two-flats, greystones, and older homes with cast-iron radiator systems.
Wide Capacity Range
10 sizes from 50–300 MBH (NG) cover everything from small single-family homes to large multi-unit buildings and commercial applications.
Technical Specifications
| Boiler Type | Hot Water & Steam configurations |
| Heat Exchanger | Cast Iron Sections with Push Nipples |
| Combustion | Atmospheric |
| Burners | Titanium composite burners |
| Venting | Chimney Vent — Integral Draft Diverter |
| Gas Types | Natural Gas (K models) / Propane (KP models) |
| Sizes Available | 10 (2–12 sections) |
| Capacity Range | 50–300 MBH input (NG) |
| Warranty | 20-Year Non-Prorated Limited (Cast-to-Last) |
| Gas Valve | Automatic redundant gas valve |
| Ignition | 24V intermittent pilot, continuous retry |
| Shut-off | 100% shut-off on continuous retry |
| Burner Assembly | Combination burner/electrode/flame sensor |
| Gas Manifold | With orifices for NG or LP |
| Circulator Relay | Included |
| Diagnostics | Indicator lights |
| Draft | Integral draft diverter + vent damper |
Capacity Ranges
K models = Natural Gas · KP models = Propane
| Model | Input MBH | Output MBH | Sections |
|---|---|---|---|
| DXL-K-050 | 50 | 42 | 2 |
| DXL-K-075 | 75 | 63 | 3 |
| DXL-K-100 | 100 | 84 | 4 |
| DXL-K-125 | 125 | 105 | 5 |
| DXL-K-150 | 150 | 126 | 6 |
| DXL-K-175 | 175 | 147 | 7 |
| DXL-K-200 | 200 | 168 | 8 |
| DXL-K-225 | 225 | 189 | 9 |
| DXL-K-250 | 250 | 210 | 10 |
| DXL-K-300 | 300 | 252 | 12 |
| Model | Input MBH | Output MBH | Sections |
|---|---|---|---|
| DXL-KP-050 | 50 | 42 | 2 |
| DXL-KP-075 | 75 | 63 | 3 |
| DXL-KP-100 | 100 | 84 | 4 |
| DXL-KP-125 | 125 | 105 | 5 |
| DXL-KP-150 | 150 | 126 | 6 |
| DXL-KP-175 | 175 | 147 | 7 |
| DXL-KP-200 | 200 | 168 | 8 |
| DXL-KP-225 | 225 | 189 | 9 |
| DXL-KP-250 | 250 | 210 | 10 |
| DXL-KP-300 | 300 | 252 | 12 |
Safety Features & Included Components
Safety Features
- Automatic redundant gas valve
- 100% shut-off on continuous retry ignition
- Flame roll-out safety shut-off (fuse link)
- Blocked vent safety shut-off (manual reset disc thermostat)
- ASME 30 lb. pressure relief valve
- Temperature/pressure gauge
- Built-in low-water cutoff (LWCO) — hot water models
- Spare fuse link included
Included Components
- Insulated boiler jacket
- Integral draft diverter
- Vent damper
- Temperature/pressure gauge
- Circulator pump (wired with 5′ harness — supply or return mounting)
- ¾″ drain valve
- 30 lb. ASME relief valve
- Combination burner/electrode/flame sensor assembly
Available Options
What's Included in the Installation
Installation Notes
- Most DXL-K replacements complete in a single day — minimal disruption to your home.
- D's Air pulls all required City of Chicago permits for every boiler installation.
- Available in both hot-water and steam configurations — ideal for Chicago two-flats and greystones with existing cast-iron radiator systems.
- Circulator pump ships pre-wired with a 5′ harness for supply or return mounting flexibility.
- Natural Gas and Propane conversion kits available for fuel-type changes at time of install.
- High-altitude conversion kits available for installations above 2,000 ft elevation.
- Integral draft diverter and vent damper reduce unit height — fits tight mechanical rooms.
- All installations include startup, system pressure test, and combustion verification.
Why D's Air & Heating, Inc.
Installed pricing includes equipment, labor, City of Chicago permits, startup, and a 1-year workmanship warranty. No hidden fees.
Small (50–75 MBH)
$6,450
DXL-K-050 / DXL-K-075 — single-family homes up to ~1,200 sq ft
Medium (100–125 MBH)
$7,250
DXL-K-100 / DXL-K-125 — single-family homes up to ~2,000 sq ft
Large (150–200 MBH)
$8,750
DXL-K-150 / DXL-K-175 / DXL-K-200 — two-flats, larger homes
XL (225–300 MBH)
$10,950
DXL-K-225 / DXL-K-250 / DXL-K-300 — large two-flats, greystones, multi-zone
Service Call Policy — D's Air & Heating, Inc.
- 1Fee covers travel and full diagnostics only.
- 2Fee is not deducted from repair or installation cost.
- 3After diagnostics, clear repair/replacement options with upfront itemized pricing.
- 4Once Maintenance Agreement approved, 15% discount activates and applies to repair/installation estimate.
- 515% discount does not apply to the initial service call fee.
A $95.35 Service Call Fee is Required for All Service Appointments, Including Warranty Claims.
Trusted American Boiler Technology
Dunkirk has been manufacturing dependable heating equipment in Dunkirk, New York since 1928. For nearly a century, Dunkirk has built a reputation for durable cast iron construction, reliable atmospheric combustion, and heating systems that stand the test of time. The DXL-K cast iron gas boiler represents the continuation of that tradition — a proven, time-tested design that Chicago homeowners and contractors have trusted for decades.
The DXL-K is purpose-built for the demands of Chicago's climate and housing stock. Chicago winters are severe, and older homes — bungalows, two-flats, greystones — rely on cast iron radiator systems that require a boiler capable of delivering consistent, reliable heat season after season. The DXL-K's heavy-duty cast iron sections provide exceptional heat retention and thermal mass, maintaining comfortable temperatures even during the coldest nights. Unlike thin-walled steel boilers, cast iron construction resists corrosion and thermal stress, contributing to a service life that can exceed 30 years with proper maintenance.
Dunkirk's Cast-to-Last 20-year non-prorated warranty on the heat exchanger reflects the company's confidence in its cast iron construction. This is one of the strongest residential boiler warranties available — and it's non-prorated, meaning the full warranty value applies throughout the entire 20-year period. For Chicago homeowners making a long-term investment in their heating system, this warranty provides genuine peace of mind.
The DXL-K is available in both hot water and steam configurations, making it uniquely versatile for Chicago's diverse housing stock. Whether your home has a one-pipe steam system, a two-pipe steam system, or a hot water baseboard or radiator system, the DXL-K can be configured to match your existing distribution system — eliminating the need for costly system conversion. Ten sizes from 50 to 300 MBH ensure proper sizing for every application, from small single-family homes to large multi-unit buildings.
Common Applications
Ideal for Chicago's diverse residential and light commercial heating needs
What Chicago Customers Say
⭐⭐⭐⭐⭐ 4.9/5 Customer Satisfaction
"D's Air replaced our old boiler with a Dunkirk DXL-K and the difference is night and day. The house heats up faster and the radiators are more consistent. Darryl and his team were professional, clean, and had everything done in one day. Highly recommend."
Marcus T.
Humboldt Park, Chicago
"We have a two-flat with a steam system and D's Air knew exactly what we needed. They installed the Dunkirk DXL-K and our tenants haven't had a single complaint about heat all winter. Great service, fair pricing, and they pulled all the permits."
Sandra R.
Logan Square, Chicago
"Called D's Air when our old boiler finally gave out in January. They came out the next day, diagnosed the problem, and had a new Dunkirk installed within two days. Excellent work and they explained everything clearly. Will use them again."
James K.
Pilsen, Chicago
"Our greystone has a one-pipe steam system and D's Air was one of the few contractors who actually understood it. They installed the Dunkirk DXL-K steam configuration and our radiators work better than they have in years. Very happy with the results."
Patricia M.
Bridgeport, Chicago
Frequently Asked Questions
How long does a Dunkirk DXL-K installation take?
Most DXL-K boiler replacements are completed in a single day. New installations may take one to two days depending on the complexity of the piping and venting. D's Air & Heating minimizes disruption to your home throughout the process.
How efficient is the Dunkirk DXL-K?
The DXL-K operates at 84% AFUE (Annual Fuel Utilization Efficiency). Its cast iron construction and proven atmospheric combustion deliver reliable, consistent heat with a long service life — making it an excellent value for Chicago homes with existing chimney venting.
Is financing available for a DXL-K installation?
Yes. D's Air & Heating offers financing options for qualified customers. Ask about current financing programs when you call for your free estimate.
How often should the DXL-K be serviced?
Annual maintenance is recommended before each heating season. Regular service includes cleaning the heat exchanger, inspecting the burners and controls, checking safety devices, and verifying combustion efficiency.
What warranty comes with the Dunkirk DXL-K?
The DXL-K includes Dunkirk's Cast-to-Last 20-year non-prorated limited warranty on the heat exchanger — one of the strongest residential boiler warranties available.
Is the DXL-K available in both hot water and steam configurations?
Yes. The DXL-K is available in both hot water and steam configurations, making it ideal for Chicago's older housing stock — greystones, bungalows, and two-flats with existing cast-iron radiator systems.
Does D's Air & Heating pull permits for boiler installations?
Yes. D's Air & Heating pulls all required City of Chicago permits for every boiler installation. Permit processing is included in the installation price.
What sizes is the DXL-K available in?
The DXL-K is available in 10 sizes from 50 MBH to 300 MBH input for natural gas, covering everything from small single-family homes to large multi-unit buildings. Propane (KP) models are also available in the same size range.
Explore More Dunkirk & Boiler Resources
Compare models, schedule service, or browse our full boiler lineup.
Why Choose D's Air & Heating, Inc.
D's Air & Heating, Inc. has been providing professional boiler installation, replacement, repair, and maintenance services throughout Chicago since 2009. Founded by Darryl Q. Joyner Sr., D's Air & Heating has built a reputation for honest recommendations, quality workmanship, and professional customer service that Chicago homeowners trust.
Choosing the right contractor is just as important as choosing the right equipment. Unlike contractors who simply swap equipment and leave, D's Air & Heating focuses on complete system performance. Our experienced technicians evaluate your home's heating needs, inspect existing piping and venting, verify proper sizing, and ensure your new Dunkirk DXL-K is installed correctly for maximum efficiency and long-term reliability.
Every boiler installation includes proper load calculations, startup procedures, safety verification, and customer training so you understand your new system. We pull all required City of Chicago permits, handle disposal of your old equipment, and leave your mechanical room clean. Our technicians are experienced with Chicago's older housing stock — bungalows, two-flats, greystones — and understand the specific requirements of steam and hot water radiator systems.
D's Air & Heating operates without contracts and without gimmicks. We provide transparent, upfront pricing before any work begins. When you call for a free estimate, you receive an honest assessment of your heating needs and a clear price — no surprises, no hidden fees. Our goal is to earn your trust through quality work and honest service, not through long-term contracts.
Ready for a new Dunkirk DXL-K boiler?
Call D's Air & Heating today at (773) 940-0965 for a free estimate. Chicago's trusted boiler contractor — no contracts, upfront pricing.
Book Online — Free EstimateWhy Chicago Homeowners Trust D's Air & Heating
Licensed & Insured
IL License #2183457
Serving Chicago
Since 2009
Authorized Dealer
Multiple Brands
No Contracts
Ever — Guaranteed
Permit Pulled
Every Installation
Professional Standards
Code-Compliant Work
EPA Certified
Mainstream Engineering
R-410A Certified
Mainstream Engineering
Why Choose D's Air & Heating, Inc.?
Chicago's trusted HVAC company since 2009 — licensed, insured, and committed to honest workmanship on every job.
Experience Since 2009
D's Air & Heating has served Chicago homeowners and businesses since 2009. Over 15 years of local HVAC experience means we've seen every type of system, every Chicago building configuration, and every challenge the city's climate presents.
Manufacturer-Trained Technicians
Our technicians receive ongoing manufacturer training and certification. We install Lennox, Goodman, Amana, Daikin, Sinclair, Weil-McLain, Peerless, and other leading brands — and we know each system inside and out.
Licensed, Insured & Permitted
D's Air & Heating holds Illinois HVAC License #2183457 and carries full liability insurance. We pull City of Chicago permits on every installation — protecting you legally and ensuring the work meets code.
Honest Recommendations
We tell you what you need — not what generates the highest invoice. If your system can be repaired cost-effectively, we'll say so. If replacement makes more sense, we'll explain exactly why. No pressure, no upselling.
Local Chicago Expertise
We know Chicago's housing stock — two-flats, greystones, bungalows, vintage buildings with steam heat, modern construction with forced air. We size and install equipment for the specific demands of Chicago homes and Chicago winters.
Long-Term Customer Support
Our relationship doesn't end at installation. We register your equipment for warranty, remain available for follow-up questions, and provide ongoing maintenance to keep your system running at peak efficiency for years.
Steam Boiler Expertise — What Chicago Building Owners Should Know
How a Steam Heating System Works
A steam boiler heats water to 212°F, producing steam that rises naturally through supply pipes to cast-iron radiators throughout the building. As the steam gives up its heat, it condenses back to water and returns to the boiler by gravity. One-pipe systems use the same pipe for both steam supply and condensate return. Two-pipe systems use separate supply and return lines, allowing better control and zoning.
The Hartford Loop — Why It Matters
The Hartford Loop is a critical safety piping arrangement on steam boilers. It prevents the boiler from losing its water level if a return pipe develops a leak. Without a properly installed Hartford Loop, a pipe failure can drain the boiler dry, causing catastrophic damage. D's Air installs the Hartford Loop correctly on every steam boiler installation.
Steam Boiler Sizing — EDR Calculations
Steam boilers are sized by Equivalent Direct Radiation (EDR) — the total radiation capacity of all the radiators in the building. The boiler must be sized to match the connected radiation, not the building's heat loss. An oversized steam boiler causes water hammer, wet steam, and rapid cycling. D's Air measures EDR on every steam boiler installation.
Water Quality and Treatment
Steam boiler water quality directly affects system performance and longevity. Impurities cause foaming, which produces wet steam and water hammer. Proper pH balance prevents corrosion of the boiler sections and pipes. D's Air tests water quality and recommends treatment on every steam boiler installation and service call.
Common Steam System Problems
The most frequent steam system issues in Chicago buildings: water hammer (banging pipes — usually caused by wet steam, improper pitch, or failed steam traps), uneven heat between floors (failed vents or traps), boiler cycling on low water (LWCO trips — check water level and return lines), and radiators that won't heat (air-bound — replace the air vent).
What to Expect From Your D's Air Steam Boiler Service
System Assessment
We inspect the boiler, near-boiler piping, Hartford Loop, vents, traps, and radiators before recommending any work.
EDR Measurement
For new installations, we measure every radiator in the building to size the replacement boiler correctly.
Written Estimate
You receive a complete written estimate covering equipment, labor, piping, and permits before any work begins.
Installation
Our crew installs the new boiler with proper near-boiler piping, Hartford Loop, and all safety controls.
Startup & Testing
We fill the system, fire the boiler, verify steam pressure, check all vents and traps, and confirm heat to every radiator.
Customer Training
We explain how to check the water level, what the pressuretrol does, and what maintenance is needed annually.
D's Air Steam Boiler Standards — Every Installation
- EDR calculation — boiler sized to match connected radiation
- Hartford Loop installed per industry standard
- Near-boiler piping per manufacturer specifications
- Equalizer pipe properly sized and connected
- Low-water cutoff tested and verified
- Pressuretrol set to correct operating pressure (typically 0.5–2 PSI)
- All steam vents and traps inspected and replaced as needed
- Water quality tested — treatment recommended if needed
- Gas pressure test and combustion analysis at startup
- City of Chicago permit pulled on every installation
What Our Customers Say
Based on Google Reviews — D's Air & Heating, Inc.
Marcus T.
Furnace Replacement
"D's Air & Heating did an outstanding job replacing my furnace. Darryl was professional, on time, and explained everything clearly. The installation was clean and the system works perfectly. Highly recommend."
Latoya W.
Boiler Repair
"Called D's Air when my boiler stopped working in January. They came out the same day, diagnosed the problem quickly, and had it running again within hours. Fair pricing and excellent service."
James R.
AC Installation
"Installed a new central AC system for us this summer. The crew was respectful of our home, cleaned up after themselves, and the system runs quietly and efficiently. Very satisfied."
Ready to Work With Chicago's Trusted HVAC Company?
D's Air & Heating, Inc. — Serving Chicago Since 2009. Licensed, Insured, No Contracts.