Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The ELX-400FBN and ELX-500FBN are the two smallest Elite XL commercial boilers and share the same 26 x 41 x 40.7 in floor cabinet, 4 in vent allowance (125 ft), 2 in NPT supply/return and natural-gas-or-LP operation. The 500 adds 101 MBH of input ceiling and 98 MBH of heating capacity for 7 lb of shipping weight; the minimum fire rises from 39,900 to 50,000 Btu/hr.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | HTP Elite XL ELX-400FBN | HTP Elite XL ELX-500FBN |
|---|---|---|
| Input rate, minimum | 39.9 MBH | 50 MBH |
| Input rate, maximum | 399 MBH | 500 MBH |
| Heating capacity | 387 MBH | 485 MBH |
| Thermal efficiency (page and submittal claim) | Up to 97% | Up to 97% |
| Turndown | Up to 10:1 | Up to 10:1 |
| Shipping weight | 538 lb | 545 lb |
| Boiler water content | 3.8 gal | 4.3 gal |
| Minimum flow rate at 20 °F ΔT at low fire | 4 GPM | 5 GPM |
| Vent size and maximum combined run | 4" adapter — 4" (125 ft) max combined, 10 ft minimum | 4" adapter — 4" (125 ft) max combined, 10 ft minimum |
| Supply / return connection | 2" NPT | 2" NPT |
| Gas connection | 1" NPT | 1" NPT |
Both models are floor-standing condensing commercial boilers on the 928 control with a 316L stainless steel water-tube heat exchanger, up to 10:1 modulation, a 160 PSI MAWP with a 50 PSI relief valve and cascade wiring for up to eight boilers. The ELX-400FBN fires 39,900–399,000 Btu/hr to 387 MBH; the ELX-500FBN fires 50,000–500,000 Btu/hr to 485 MBH.
The physical package barely changes: shipping weight moves from 538 to 545 lb and boiler water content from 3.8 to 4.3 gal in the identical cabinet, with the same 4 in vent adapter (125 ft maximum combined run, 10 ft minimum). Both connect 2 in NPT supply/return with a 1 in NPT gas inlet.
The meaningful difference is the bottom of the range and the minimum flow: the 400 fires down to 39,900 Btu/hr with a 4 GPM minimum flow at a 20 °F ΔT, while the 500 starts at 50,000 Btu/hr with 5 GPM. In a plant whose load rarely exceeds 400 MBH, the smaller boiler's lower floor is the reason to stay at the 400.
The HTP Elite XL ELX-400FBN is the 399 MBH class model of HTP's current commercial condensing line: 39.9 to 399 MBH input, 387 MBH heating capacity, a 316L stainless steel water-tube heat exchanger and up to 10:1 modulation in a 538 lb floor-standing cabinet.
The HTP Elite XL ELX-500FBN is the 500 MBH class model of HTP's current commercial condensing line: 50 to 500 MBH input, 485 MBH heating capacity, a 316L stainless steel water-tube heat exchanger and up to 10:1 modulation in a 545 lb floor-standing cabinet.
Yes — both are the 26 x 41 x 40.7 in cabinet with the same 4 in vent adapter; the 500 is 7 lb heavier at 545 lb shipping.
The ELX-400FBN, from 39,900 Btu/hr against the 500's 50,000 Btu/hr, with a lower 4 GPM minimum flow at a 20 °F ΔT.
Yes — LP-691 prints the 400–1000 models for natural or LP gas operation at 3.5–14 in. w.c.; the 1500 and 2000 models are natural gas only.
A consultation includes a heat-loss review so the size is right the first time.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.