The HTP UFT (Ultra-Fire Tankless) Combi is the brand's residential condensing combination heater — providing both space heating and domestic hot water from a single high-efficiency wall-hung unit. Combi units consolidate what would otherwise be a separate boiler + indirect tank into one product, saving wall space and reducing install complexity in tight mechanical rooms.
How combi units work
A combi has two heat exchange paths: a primary heat exchanger heated by the modulating burner, and a secondary plate heat exchanger that transfers heat from the primary loop water to incoming cold domestic water on demand. When you call for hot water at a fixture, the unit activates the secondary exchanger and delivers tankless-style hot water flow. When the thermostat calls for space heating, the unit circulates primary loop water through baseboard, radiant, or air handler.
UFT Combi sizing
HTP UFT models range from 80,000 BTU/hr (UFT-80W) to 199,000 BTU/hr (UFT-199W). Sizing depends on simultaneous heating + DHW demand:
- UFT-80W: small home, 1–2 baths, mild climate
- UFT-100W: mid-size home, 2 baths, moderate climate
- UFT-140W: larger home, 2–3 baths, cold climate
- UFT-175W and UFT-199W: large homes or homes with high simultaneous DHW demand
Combi vs separate boiler + indirect
Combi advantages:
- Single appliance, single warranty, single service contract
- Smaller wall footprint vs boiler + tank
- Lower total install cost (single set of gas, vent, electrical, water connections)
- Modern condensing efficiency on both heating and DHW
Separate boiler + indirect advantages:
- Higher DHW capacity (tank buffer + boiler recovery vs combi instantaneous)
- Better simultaneous heating + DHW handling
- Longer lifespan typical (separate components age independently)
DHW capacity reality
Combi DHW flow depends on temperature rise — UFT-100W delivers approximately 4.0 GPM at 70°F rise (cold inlet 50°F → 120°F outlet). In cold climates with 40°F inlet water, the same unit delivers about 3.0 GPM at the same outlet temperature. For households with simultaneous 2-shower demand at peak flow, sizing up matters.
Installation specifics
- Gas line: typically 3/4" required (verify with HTP sizing chart based on line length)
- Venting: concentric or twin-pipe per HTP specifications
- Electrical: 120V dedicated circuit, typically 15A
- Water connections: 3/4" cold inlet, 3/4" hot outlet for DHW
- Heating loop: 1" supply and return to heating zones
- Condensate drain: neutralized condensate from condensing heat exchanger
Cold-water-sandwich behavior on combi
Combi DHW has a slight cold patch during interruptions, similar to standalone tankless. Some combis (HTP and others) implement "preheated mode" where a small buffer is maintained for instant hot — this reduces sandwich at slight efficiency cost. Verify your UFT model's specific behavior with the installer.
Efficiency rating
UFT combi delivers 95% AFUE on space heating and 0.92+ UEF on DHW. Compared to a standard tank gas water heater at 0.62 EF and an 85% AFUE conventional boiler, the efficiency gain is substantial — typical operating cost reduction of 25–40% vs older separate systems.
HTP UFT vs competitors
UFT competes with Navien NCB, Lochinvar WHN, Triangle Tube Challenger, and Viessmann Vitodens combi units. UFT is typically priced competitively in the mid-range; Navien NCB has the broader installer network. For installations where the installer is HTP-familiar, UFT is a strong pick.