Lochinvar · Knight XL Commercial (KBX)
Lochinvar Knight XL KBX0800
The Knight XL KBX0800 fires 80 to 800 MBH with 776 MBH gross output and a 675 MBH AHRI net rating at 97% thermal efficiency, keeping 2" water connections with a 6" vent.
Key figures
- Max input
- 800 MBH
- Max CSA output
- —
- AFUE
- —
- Min input
- 80 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Lochinvar Knight XL KBX0800 in practice
The KBX0800 carries the Knight XL Commercial line into 800 MBH territory: the I&O ratings table lists 80 to 800 MBH input with 776 MBH gross output and a 675 MBH AHRI net water rating at 97% thermal efficiency. Water content grows to 7.3 gallons while the water connection stays 2" and the gas connection stays 1-1/4", with a 4" air intake and 6" vent.
It is the same floor-mounted stainless steel water-tube condensing platform as the rest of the line — SMART TOUCH control, CON·X·US, ENERGY STAR and ASME H — vented in PVC, CPVC, polypropylene, ABS or stainless steel to 150 equivalent feet per the submittal. The submittal prints a 484 lb shipping weight for the KBX0800, and the common vent kit (KBX0500-KBX1000) covers this size.
Best suited to
- Commercial heating plants with design-day loads between 650 and 800 MBH
- Schools and larger institutional buildings named in Lochinvar's Knight XL positioning
- Projects that hold 2" water piping through an 800 MBH ceiling
Applicability and support
- Model number
- KBX0800
- 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 | 80 MBH | Per the I&O ratings table. |
| Heating input, maximum | 800 MBH | Per the I&O ratings table. |
| Output | ||
| Gross output | 776 MBH | Per the I&O ratings table. |
| Net AHRI water rating | 675 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 | 6" | 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 | 7.3 gal | Per the I&O ratings table. |
| Space-heating water connections | 2" | Per the I&O ratings table. |
| Gas connection | 1-1/4" | Per the I&O ratings table. |
| Shipping weight | 484 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 KBX0800's ratings?
80 to 800 MBH of input with 776 MBH gross output and a 675 MBH AHRI net water rating at 97% thermal efficiency, per the I&O ratings table.
Does the KBX0800 need larger venting than the KBX0650?
No — both print 4" air intake and 6" vent in the ratings table. The step from the KBX0650 is capacity: 800 against 650 MBH maximum input and 776 against 631 MBH gross output.
Questions about the Lochinvar Knight XL KBX0800?
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.