Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The Mod Con 500 and 700 share the same 20.5 x 36 x 46 in cabinet, 4 in vent (200 ft), 2 in NPT supply/return, 505 lb shipping weight and 33 GPM minimum flow. The 700 adds 200 MBH of input ceiling and 216 MBH of heating capacity, prints the line's best 98% thermal efficiency against the 500's 94%, but raises the minimum fire from 100,000 to 170,000 Btu/hr.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | HTP Mod Con 500 | HTP Mod Con 700 |
|---|---|---|
| Input rate, minimum | 100 MBH | 170 MBH |
| Input rate, maximum | 500 MBH | 700 MBH |
| Heating capacity | 470 MBH | 686 MBH |
| Thermal efficiency | 94 % | 98 % |
| Turndown | Up to 5:1 | Up to 5:1 |
| Shipping weight | 505 lb | 505 lb |
| Boiler water content | 4.2 gal | 4.2 gal |
| Minimum flow rate at 30 °F ΔT | 33 GPM | 33 GPM |
| Vent size and maximum combined run | 4" (200 ft) max combined, 16 ft minimum | 4" (200 ft) max combined, 16 ft minimum |
| Supply / return connection | 2" NPT | 2" NPT |
| Gas inlet | 1-1/2" NPTF | 2" NPTF |
Both are floor-standing 316L stainless steel water-tube condensing boilers from HTP's discontinued Mod Con line, on the 926 control with up to 5:1 turndown, a 160 PSI MAWP, a 75 PSI relief valve, 200 equivalent feet of Category IV venting and cascade wiring for eight boilers. The 500 fires 100,000–500,000 Btu/hr to 470 MBH; the 700 fires 170,000–700,000 Btu/hr to 686 MBH.
The published package is identical: 505 lb shipping, 4.2 gal water content, 33 GPM minimum flow at a 30 °F ΔT, the same 4 in vent, 2 in NPT supply/return and a 1-1/2 in NPTF gas inlet on the 500 against 2 in NPTF on the 700. Only the firing range and the printed efficiency differ.
The 700 carries the line's best printed figure at 98% thermal efficiency, against 94% for both the 500 and 850 — an as-printed result rather than a size trend. Its 170,000 Btu/hr minimum fire is 70% higher than the 500's, so a plant with a persistent low load should weigh that against the extra ceiling.
The HTP Mod Con 500 is the 500 MBH class model of HTP's discontinued commercial condensing boiler line: 100 to 500 Btu/hr input, 470 MBH heating capacity and 94% printed thermal efficiency in a 505 lb floor-standing cabinet.
The HTP Mod Con 700 is the 700 MBH class model of HTP's discontinued commercial condensing boiler line: 170 to 700 Btu/hr input, 686 MBH heating capacity and 98% printed thermal efficiency in a 505 lb floor-standing cabinet.
The Mod Con 700 at 98% thermal efficiency; the 500 and 850 both print 94% in the official table.
Yes — 20.5 x 36 x 46 in, 505 lb shipping and 4.2 gal water content each; the gas inlet steps from 1-1/2 in NPTF to 2 in NPTF on the 700.
No — the discontinued-products index lists 'Mod Con Commercial Gas Boiler'; the manuals remain for support.
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.