Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
Boilers.ca is a brand of ROMA Heating & Cooling · Licensed gas contractor LGA0202903
Comparison
Verdict in brief
The Mod Con 850 is the largest size in the discontinued Mod Con line: it keeps the 700's 170,000 Btu/hr minimum fire but lifts the ceiling to 850,000 Btu/hr and heating capacity to 799 MBH, deepens the cabinet to 68.5 in, moves to a 6 in vent, and ships 75 lb heavier with 5.8 gal of water content. Its printed thermal efficiency is 94% against the 700's 98%.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | HTP Mod Con 700 | HTP Mod Con 850 |
|---|---|---|
| Input rate, minimum | 170 MBH | 170 MBH |
| Input rate, maximum | 700 MBH | 850 MBH |
| Heating capacity | 686 MBH | 799 MBH |
| Thermal efficiency | 98 % | 94 % |
| Turndown | Up to 5:1 | Up to 5:1 |
| Shipping weight | 505 lb | 580 lb |
| Boiler water content | 4.2 gal | 5.8 gal |
| Minimum flow rate at 30 °F ΔT | 33 GPM | 54 GPM |
| Vent size and maximum combined run | 4" (200 ft) max combined, 16 ft minimum | 6" (200 ft) max combined, 16 ft minimum |
| Supply / return connection | 2" NPT | 2" NPT |
| Gas inlet | 2" NPTF | 2" NPTF |
Both models fire from the same 170,000 Btu/hr minimum, so below the 700's ceiling they modulate identically. The 850 raises the maximum input to 850,000 Btu/hr and heating capacity to 799 MBH against the 700's 686 MBH, with the minimum flow at a 30 °F ΔT rising from 33 to 54 GPM.
The physical step is real: the 850 deepens the cabinet from 46 to 68.5 in, moves to a 6 in vent (still 200 ft maximum), ships at 580 lb against 505 lb, holds 5.8 gal of water against 4.2 gal, and uses a 2 in NPTF gas inlet like the 700.
Efficiency reverses: the page table prints 94% for the 850 against the 700's 98%. Both carry the 926 control, up to 5:1 turndown, 160 PSI MAWP with a 75 PSI relief valve, and the 10-year limited warranty of the retired line.
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 HTP Mod Con 850 is the 850 MBH class model of HTP's discontinued commercial condensing boiler line: 170 to 850 Btu/hr input, 799 MBH heating capacity and 94% printed thermal efficiency in a 580 lb floor-standing cabinet.
The Mod Con 850 at 850,000 Btu/hr input and 799 MBH heating capacity, against the 700's 700,000 Btu/hr and 686 MBH.
Yes — both print a 170,000 Btu/hr minimum input; the 850's minimum flow rate at a 30 °F ΔT is higher at 54 GPM against 33 GPM.
No — the 850 uses a 6 in vent adapter against the 700's 4 in; both allow 200 equivalent feet combined.
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.