Lochinvar · Knight XL Commercial (KBX)
Lochinvar Knight XL KBX0500
The Knight XL KBX0500 steps the commercial Knight XL to 50 to 500 MBH input with 485 MBH gross output and a 422 MBH AHRI net rating at 97% thermal efficiency, on 2" water connections.
Key figures
- Max input
- 500 MBH
- Max CSA output
- —
- AFUE
- —
- Min input
- 50 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Lochinvar Knight XL KBX0500 in practice
The KBX0500 is the second size of the Knight XL Commercial line, adding 101 MBH of ceiling over the KBX0400: the I&O ratings table lists 50 to 500 MBH input with 485 MBH gross output and a 422 MBH AHRI net water rating at 97% thermal efficiency. Its 4.9-gallon water content stays on 2" water and 1" gas connections, and the same 4" air intake and 4" vent sizes apply.
Like every Knight XL it is a floor-mounted stainless steel water-tube condensing boiler with the SMART TOUCH control and CON·X·US, ENERGY STAR certification and an ASME H stamp per the family's product page and I&O note. Venting is room air/direct vent in PVC, CPVC, polypropylene, ABS or stainless steel to 150 equivalent feet per the submittal (which also lists the common vent kit for the KBX0500-KBX1000 sizes), and the submittal prints a 377 lb shipping weight.
Best suited to
- Commercial loads between the 400 and 500 MBH marks on a design day
- Plants where the 50 MBH minimum fire and 4" air/vent sizing fit the mechanical room
- Step-up projects that keep 2" water piping with a 500 MBH ceiling
Applicability and support
- Model number
- KBX0500
- 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 | 50 MBH | Per the I&O ratings table. |
| Heating input, maximum | 500 MBH | Per the I&O ratings table. |
| Output | ||
| Gross output | 485 MBH | Per the I&O ratings table. |
| Net AHRI water rating | 422 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 | 4.9 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 | 377 lb | Shipping weight per the KBX submittal. |
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 are the KBX0500's ratings?
50 to 500 MBH of input with 485 MBH gross output and a 422 MBH AHRI net water rating at 97% thermal efficiency, per the I&O ratings table.
How does the KBX0500 compare with the KBX0400?
Maximum input rises from 399 to 500 MBH and gross output from 387 to 485 MBH, while the water connection stays 2" and the air intake and vent stay 4"; the minimum fire rises from 39.9 to 50 MBH.
Questions about the Lochinvar Knight XL KBX0500?
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.
Compare and explore
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.