Navien · NFB-C Commercial Boiler
Navien NFB-399C
The Navien NFB-399C is the top model of the wall-hung NFB-C commercial boiler series: 26 to 399 MBH of input with a 389 MBH heating capacity and a 338 MBH net AHRI water rating at 97.5% thermal efficiency, in the same cabinet as the NFB-301C at 278 lb.
Key figures
- Max input
- 399 MBH
- Max CSA output
- —
- AFUE
- —
- Min input
- 26 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Navien NFB-399C in practice
The NFB-399C fires from 26,000 to 399,000 BTU/h of input at a printed 97.5% thermal efficiency, with the product page listing a 389,000 BTU/h capacity and a 338,000 BTU/h net AHRI water rating (net figures are based on a piping and pickup allowance of 1.15) and a 15:1 turndown in its input/turndown table. It is certified under AHRI certificate no. 201928625 with CRN registration R6290.5 printed on the page, and its safety devices are listed as a flame rod, air pressure switch, ignition operation detector, water high-limit switch, exhaust high-limit sensor and water pressure sensor.
At 25.1 x 32.8 x 22.3 in it shares the NFB-C cabinet with the NFB-301C but is the heavier of the two at 278 lb, holding 9.6 gallons of water on 1 1/4" NPT water and 3/4" NPT gas connections. Venting matches the 301C: 3" or 4" PVC, CPVC, polypropylene or stainless steel (or special gas vent Type BH, Class III A/B/C) in forced-draft direct-vent or single-pipe non-direct-vent configurations, with the series page allowing 3" runs to 60 ft or 4" to 150 ft.
Best suited to
- Commercial space-heating loads whose heat-loss or plant calculation needs the 399 MBH ceiling
- Wall-hung installations that want the largest NFB-C size without a floor-standing cabinet
- Multi-boiler plants where the 301C and 399C sizes are mixed across cascade stages
Applicability and support
- Model number
- NFB-399C
- 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 Navien. Units are shown with every value; notes flag conflicting sources or missing figures.
| Specification | Value | Note |
|---|---|---|
| Input | ||
| Input, minimum | 26 MBH | 26,000 BTU/h space-heating input, per the product page. |
| Input, maximum | 399 MBH | 399,000 BTU/h space-heating input, per the product page. |
| Output | ||
| Heating capacity | 389 MBH | 389,000 BTU/h capacity, per the product page. |
| Net AHRI water rating | 338 MBH | 338,000 BTU/h; the net AHRI figure is based on a piping and pickup allowance of 1.15, per the product page. |
| Efficiency | ||
| Thermal efficiency | 97.5 % | As printed on the product page (DOE test basis); the page labels the row "Thermal Efficiency", not AFUE. |
| Venting and air | ||
| Venting | 3" or 4" PVC, CPVC, polypropylene or stainless steel, or 3" or 4" special gas vent Type BH (Class III A/B/C) | Forced-draft direct vent and non-direct vent (single pipe), per the product page. |
| Max. vent length, 3" | 60 ft | 3" venting up to 60 ft, per the NFB-C series page. |
| Max. vent length, 4" | 150 ft | 4" venting up to 150 ft, per the NFB-C series page. |
| Physical and connections | ||
| Weight | 278 lb | 278 lb without water per the product page; the page does not print a with-water weight. |
| Width | 25.1 in | |
| Height | 32.8 in | |
| Depth | 22.3 in | |
| Water content | 9.6 gal | Per the product page. |
| Heating water connections | 1 1/4" NPT | Per the product page. |
| Gas connection | 3/4" NPT | Per the product page. |
| Operating limits and other | ||
| Fuel | Natural gas or propane | The product page states ratings are the same for natural-gas models converted to propane use. |
| Turndown ratio | 15:1 | Printed on the product page's input/turndown table and on the NFB-C series page. |
| Water pressure rating | 12 – 160 psi | 12–160 PSI water pressure range printed on the NFB-C product pages. |
| Altitude rating | 10,100 ft | Per the NFB-C series page. |
Manuals
- NFB-C Installation and Operation Manual (EN)Ver 1.0 · 2024-02
- NFB-C Service Manual (EN)250116
Alerts documented for this model
Frequently asked questions
What is the input range of the NFB-399C?
26,000 to 399,000 BTU/h, per the product page, with a 389,000 BTU/h heating capacity and a 338,000 BTU/h net AHRI water rating at 97.5% thermal efficiency.
How much water does the NFB-399C hold?
9.6 gallons per the product page, against 7.6 gallons on the NFB-301C; the 399C also weighs more (278 lb against 243 lb) in the same 25.1 x 32.8 x 22.3 in cabinet.
Which NFB-C model should a project choose?
The 399C earns its place when the calculated load approaches the 301C's 301 MBH ceiling. Its minimum input is higher (26 MBH against 20 MBH), so a load that fits the smaller model gains steadier low-fire behaviour from the 301C.
Questions about the Navien NFB-399C?
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
- Navien Canada — NFB-C series · accessed September 9, 2026
- Navien Canada — NFB-399C product page · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.