Lochinvar · Knight XL Commercial (KBX)
Lochinvar Knight XL KBX0400
The Knight XL KBX0400 is the entry commercial Knight XL: 39.9 to 399 MBH input at 97% thermal efficiency, printing 387 MBH gross and a 337 MBH AHRI net rating, with 2" water connections and 4" air and vent sizes.
Key figures
- Max input
- 399 MBH
- Max CSA output
- —
- AFUE
- —
- Min input
- 39.9 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Lochinvar Knight XL KBX0400 in practice
The KBX0400 opens the floor-standing Knight XL Commercial line at 399,000 BTU/hr of maximum input while firing down to 39,900 (10:1 turndown). The I&O ratings table (Series 100-101) lists 39.9 to 399 MBH input, 387 MBH gross output and a 337 MBH AHRI net water rating at 97% thermal efficiency, with 4.4 gallons of water content on 2" water and 1" gas connections.
Its product page — the default KBX0400N-100 page for the line — prints the stainless steel water-tube heat exchanger, SMART TOUCH control with CON·X·US, ENERGY STAR certification, an ASME H stamp, a 365 lb shipping weight, a 45.125" height and 24" width, and a 10-year heat exchanger with 1-year parts warranty. The unit vents in 4" air intake and 4" vent with PVC, CPVC, polypropylene, ABS or stainless steel pipe to 150 equivalent feet per the submittal, and Lochinvar's Canada English page is identical to the United States page.
Best suited to
- Commercial buildings and plant rooms whose design-day load fits under 399 MBH
- School, hotel and healthcare projects named in Lochinvar's Knight XL positioning
- Systems that want a 39.9 MBH minimum fire on a 399 MBH commercial boiler
Applicability and support
- Model number
- KBX0400
- Canadian availability
- available
- Production status
- current
- ROMA supplies
- Confirmed at consultation
- ROMA services
- Confirmed at consultation
- Warranty
- Series terms
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Specifications
Published specifications
Values as published by Lochinvar. Units are shown with every value; notes flag conflicting sources or missing figures.
| Specification | Value | Note |
|---|---|---|
| Input | ||
| Heating input, minimum | 39.9 MBH | Per the I&O ratings table. |
| Heating input, maximum | 399 MBH | Per the I&O ratings table. |
| Output | ||
| Gross output | 387 MBH | Per the I&O ratings table. |
| Net AHRI water rating | 337 MBH | Net AHRI rating based on a piping and pickup allowance of 1.15, per the I&O rating notes. |
| Efficiency | ||
| Efficiency (thermal) | 97 % | 97% thermal efficiency per the product-page spec block; the KBX submittal prints 97.0%. |
| Venting and air | ||
| Air inlet size | 4" | Per the I&O ratings table. |
| Vent size | 4" | Per the I&O ratings table. |
| Venting | Category IV sealed combustion; room air/direct vent in PVC, CPVC, polypropylene, ABS or stainless steel | Direct-vent vertical or horizontal up to 150 equivalent feet per the KBX submittal; concentric vent kit KBX0400-KBX650 and common vent kit KBX0500-KBX1000 listed among the submittal venting options. |
| Physical and connections | ||
| Water content | 4.4 gal | Per the I&O ratings table. |
| Space-heating water connections | 2" | Per the I&O ratings table. |
| Gas connection | 1" | Per the I&O ratings table. |
| Shipping weight | 365 lb | Shipping weight per the KBX submittal. |
| Height | 45.125 in | Per the Lochinvar product page. |
| Width | 24 in | Per the Lochinvar product page. |
Manuals
Alerts documented for this model
- Gas Pressure SW
- Flow Switch/LWCO
- Blocked Drain SW/HEX O-Temp SW
- APS Open
- Anti-cycling
- Flame Fail Ign
- Flame Sequence
- Outlet ARHL
- Outlet MRHL
- Fan Low/High OR Fan Speed Low/High
- Sensor Open
- Sensor Shorted
- Louver Proving Sw
- Inlet Sensor Fault
- Outlet Sensor Fault
- Outlet Temp Diff
- Flue Sensor Fault
- Flue Temp Diff
- Flue Temp Limit
- Fatal Error
- Memory Error
- Flue Temp High
- Delta T High
- Outlet Temp High
- Rem Ctrl Flt
- Parameters Progr
- Service Blk
- Low 24 vac
- Watch Dog Error
- Write EEProm
- CRC Parameters
- No Error Stored
Frequently asked questions
What is the KBX0400's firing range?
39.9 to 399 MBH of input per the I&O ratings table, with 387 MBH gross output and a 337 MBH AHRI net water rating at 97% thermal efficiency.
How is the KBX0400 vented?
Room air/direct vent: 4" air intake and 4" vent per the ratings table, in PVC, CPVC, polypropylene, ABS or stainless steel, to 150 equivalent feet per the submittal.
Questions about the Lochinvar Knight XL KBX0400?
Describe what the boiler is doing and get a straight answer about the next step.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
- Lochinvar — Knight XL Commercial Boiler (KBX0400N) model page · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.