Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
HTP Mod Con 500 and HTP Mod Con 850 are two condensing boilers from the HTP Mod Con Commercial Gas Boiler line. The HTP Mod Con 500 is documented at 100–500 MBH input, 470 MBH heating capacity and 94% thermal efficiency, while the HTP Mod Con 850 is documented at 170–850 MBH input, 799 MBH heating capacity and 94% thermal efficiency. HTP Mod Con 850 lists 350 MBH more input than HTP Mod Con 500 (850 MBH against 500 MBH). Both list the same published thermal efficiency of 94%. HTP Mod Con 850 lists 75 lb more shipping weight than HTP Mod Con 500 (580 lb against 505 lb).
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 850 |
|---|---|---|
| Input rate, minimum | 100 MBH | 170 MBH |
| Input rate, maximum | 500 MBH | 850 MBH |
| Heating capacity | 470 MBH | 799 MBH |
| Thermal efficiency | 94 % | 94 % |
| Turndown | Up to 5:1 | Up to 5:1 |
| Boiler water content | 4.2 gal | 5.8 gal |
| Shipping weight | 505 lb | 580 lb |
| Dimensions (W x H x D) | 20.5" W x 36" H x 46" D | 20.5" W x 36" H x 68.5" D |
| Minimum flow rate at 30 °F ΔT | 33 GPM | 54 GPM |
| Power supply | 120 V / 60 Hz, 6.3 A | 120 V / 60 Hz, 6.3 A |
| Supply / return connection | 2" NPT | 2" NPT |
| Gas inlet | 1-1/2" NPTF | 2" NPTF |
| Vent size and maximum combined run | 4" (200 ft) max combined, 16 ft minimum | 6" (200 ft) max combined, 16 ft minimum |
| Heat exchanger | 316L stainless steel water tube, 160 PSI ASME stamped, National Board listed, gasketless | 316L stainless steel water tube, 160 PSI ASME stamped, National Board listed, gasketless |
| Water pressure | Heat exchanger MAWP 160 psi; ASME 75 psi relief valve | Heat exchanger MAWP 160 psi; ASME 75 psi relief valve |
| Control | 926 SIT digital control with LCD and LED indicators | 926 SIT digital control with LCD and LED indicators |
| Approved vent materials | PVC, CPVC, polypropylene or stainless steel | PVC, CPVC, polypropylene or stainless steel |
| Safety devices | Flame rectifier probe, water temperature high limit switch (190 °F), freeze protection, condensate trap with overflow switch, included low-water cut-off, blocked vent pressure switch | Flame rectifier probe, water temperature high limit switch (190 °F), freeze protection, condensate trap with overflow switch, included low-water cut-off, blocked vent pressure switch |
| Warranty | 10-year limited warranty, no registration required | 10-year limited warranty, no registration required |
Published ratings: the HTP Mod Con 500 is rated 100–500 MBH input, 470 MBH heating capacity and 94% thermal efficiency; the HTP Mod Con 850 is rated 170–850 MBH input, 799 MBH heating capacity and 94% thermal efficiency. HTP Mod Con 850 lists 350 MBH more input than HTP Mod Con 500 (850 MBH against 500 MBH). Both list the same published thermal efficiency of 94%.
HTP Mod Con 850 lists 75 lb more shipping weight than HTP Mod Con 500 (580 lb against 505 lb). The boiler water content differs: the HTP Mod Con 500 lists 4.2 gal, while the HTP Mod Con 850 lists 5.8 gal. The dimensions differs: the HTP Mod Con 500 lists 20.5" W x 36" H x 46" D, while the HTP Mod Con 850 lists 20.5" W x 36" H x 68.5" D. The minimum flow rate at 30 °F δt differs: the HTP Mod Con 500 lists 33 GPM, while the HTP Mod Con 850 lists 54 GPM.
Both records print the same thermal efficiency (94%), turndown (Up to 5:1), electrical requirement (120 V / 60 Hz, 6.3 A) and supply / return connection (2" NPT), per the cited sources.
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 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 HTP Mod Con 850 lists 850 MBH, against 500 MBH on the HTP Mod Con 500, per the cited documentation.
Both list the same thermal efficiency of 94%.
It ships at 580 lb against 505 lb for the HTP Mod Con 500, per the cited sources.
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.