The Demand Duo is Rinnai's unique hybrid product — a tankless burner module paired with an 80-gallon insulated storage tank. It solves problems that pure tankless can't (cold sandwich, short-draw activation lag, simultaneous-fixture limits) without the standby losses of a pure tank.
Models
- CHS19980HiN — 199 kBTU tankless burner + 80-gallon buffer tank, indoor NG
Also available in commercial configurations with larger buffer tanks and racked multi-tankless arrays.
How it works
- The tankless burner heats a recirculation loop through the 80-gallon storage tank
- Stored hot water is available for instant high-volume draws (multiple showers, large fill)
- Burner cycles to maintain tank temperature
- For continuous high-demand periods, burner runs continuously and effectively acts like a tankless
When Demand Duo is the right answer
- Very large homes — 5+ bathrooms or with whole-house body-spray showers. Pure tankless can't deliver 15+ GPM continuously
- Cold-climate homes with 40°F+ incoming water and high simultaneous draw demand
- Commercial applications — restaurants, salons, multi-unit residential
- Homes that hated their tankless — usually because of cold-sandwich, short-draw issues, or undersized installations
- Whole-house recirculation applications where pure tankless struggles to maintain loop temperature
When Sensei or Sensei RX is better
- Standard 2-4 bathroom homes — Sensei handles this just fine and costs much less
- Budget-sensitive installs — Demand Duo is significantly more expensive
- Limited mechanical room space — the 80-gallon tank is large
Cost
- Demand Duo CHS19980HiN: $3,500-4,500 (parts only)
- Installation: $2,500-5,000 depending on plumbing changes
- Total installed: $6,000-9,500
Warranty
12 years heat exchanger / 5 years parts / 1 year labor — residential. See warranty hub.
Bottom line
Demand Duo is a niche product — but for the right niche, it's the only Rinnai answer. Large luxury homes, problematic existing tankless installs, and small commercial. For standard residential, the savings vs Sensei don't justify the complexity.