Types of Gas Boilers
"Boiler" is a broad category. Modern boilers vary by combustion technology (condensing vs non-condensing), configuration (combi vs heating-only), construction (stainless vs cast iron), and scale (residential vs commercial). Here's how to think about each type.
Combi (Combination) Boiler
Heat + DHW in one wall-mounted unit
Pros
- No separate water tank — saves floor space
- Endless hot water
- High efficiency (95% AFUE)
- Lower install cost than heating + tank combo
- Easy to retrofit
Cons
- DHW flow is limited by boiler firing rate
- Higher complexity = more potential failure points
- Slightly slower DHW response than tank
Best for: Condos, townhomes, small to medium single-family homes
Examples: Navien NCB-E/NCB-H, IBC SL, Rinnai M-Series, Viessmann 100-W combi, Burnham Alta
Heating-Only (System) Boiler
Heating only — DHW comes from separate tank
Pros
- Higher DHW capacity via indirect tank
- Simpler boiler = fewer failure points
- Easier to service
- Better for large homes / multi-bathroom
Cons
- Requires separate water heater
- More floor space
- Higher total install cost
- Tank standby losses
Best for: Larger homes, multi-bathroom homes, hydronic-only systems
Examples: Navien NHB, Navien NFB, IBC V-Series, Weil-McLain ECO, Burnham Aspen
Condensing Boiler
Up to 98% AFUE — recovers heat from flue gases
Pros
- Highest efficiency (92-98%)
- Lower gas bills
- Stainless steel heat exchanger
- Sealed combustion (safer)
- Eligible for FortisBC/CleanBC rebates
Cons
- Requires condensate drain
- Sensitive to water chemistry
- Slightly higher up-front cost
- Sensitive to return water temperature
Best for: Almost every BC home replacing a boiler — recommended for 95%+ of new installs
Examples: All Navien, IBC, Viessmann, Rinnai, Rheem condensing models
Non-Condensing (Conventional) Boiler
Older, simpler technology — 80-85% AFUE
Pros
- Lower up-front cost
- Less sensitive to water chemistry
- Simpler service
- No condensate drain required
Cons
- Significantly higher gas bills
- Limited modern controls
- Larger physical footprint
- Not eligible for most rebates
Best for: Replacement-in-kind for older atmospheric installs where condensing retrofit is impractical
Examples: Bradford White Brute, older cast-iron lineups
Cast Iron Boiler
Traditional construction — 85-92% AFUE
Pros
- Extremely durable (often 25-30 year life)
- Robust construction
- Easier to service
- Better tolerance for water quality
Cons
- Lower efficiency than stainless condensing
- Heavier — installation logistics matter
- Larger footprint
Best for: Traditional radiator systems, long-term durability seekers, heritage homes
Examples: Weil-McLain GV90+, Burnham Independence
Commercial Boiler
High BTU, often cascaded — 200,000-2,000,000 BTU
Pros
- High capacity for multi-unit buildings
- Cascade-capable for modulating demand
- BMS integration (BACnet/Modbus)
- Heavy-duty construction
Cons
- Significant install complexity
- Permits and inspections more involved
- Higher up-front investment
Best for: Strata buildings, hotels, schools, commercial facilities
Examples: IBC HC, Viessmann Vitocrossal 300, Bradford White Brute Elite, Weil-McLain Evergreen
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