Demand Duo: Continuous flow with storage backup

Combines the benefits of continuous flow and storage—high output and minimal storage loss without limiting peak flow rate.

Demand Duo: Continuous flow with storage backup

  • Cost effective installation with pre-constructed skids
  • Connect multiple skids in parallel for larger systems
  • Compatible with circulating ring mains
  • Cost effective and easier to maintain than boiler systems
  • Competitive five year warranty on the Demand Duo cylinder

Ideal for commercial applications where the total water drawn during the day's peak is known, but the rate of water use varies. For example; central hot water systems for hotels, motels, and apartment blocks.

Hard or aggressive water will need to be treated in order to use this system, if in doubt please test before use.

For commercial applications the water heating system must be sized and installed to written guidelines from Rinnai.


398-995 MJ/h


94-225.5 kW
Model Code Configuration Input
Approx. weight
when full(kg)
DD 400 ext RCWDD400E315N/L 2 x HD200 ext 398 94 510
DD 600 ext RCWDD600E315N/L 3 x HD200 ext 597 141 540
DD 800 ext RCWDD800E315N/L 4 x HD200 ext 796 188 590
DD 1000 ext RCWDD1000E315N/L 5 x HD200 ext 995 235 620
DD 400 int RCWDD400FF315N/L 2 x HDi200 int 390 90.2 510
DD 600 int RCWDD600FF315N 3 x HDi200 int 858 135.3 545
DD 800 int RCWDD800FF315N 4 x HDi200 int 780 180.4 595
DD 1000 int RCWDD1000FF315N 5 x HDi200 int 975 225.5 630
DD 420 ext customised 2 x EF50 ext 422 111.2 545
DD 630 ext customised 3 x EF250 ext 633 166.8 590
DD 840 ext customised 4 x EF250 ext 844 222.4 665
DD 500 ext customised 2 x HD250 ext 500 119.8 530
DD 750 ext customised 3 x HD250 ext 750 179.7 570
DD 420 int customised 2 x EFi250 int 422 111.2 545
DD 620 int customised 3 x EFi250 int 633 166.8 590
DD 840 int customised 4 x EFi250 int 844 222.4 665
Refer p. 6 of the installation guide (PDF document below)
Connections Gas - 32 mm Water - 32 mm TPR - 20 mm
Gas (NG): 1.13-3.5 kPa Gas (LPG): 2.75 kPa Water: 700 kPa
Grunfos CM5-2
IPX4 (cylinder, control box, and Rinnai INFINITY)

All dimensions are in mm.

Demand Duo continuous flow with storage backup system dimensions diagrams

Model INFINITY 'A' dimensions
total width of system - mm)
DD 400 external and internal 2 x HD200/HDi200 1770
DD 600 external and internal 3 x HD200/HDi200 2240
DD 800 external and internal 4 x HD200/HDi200 2540
DD 1000 external and internal 5 x HD200/HDi200 2920
DD 420 external and internal 2 x EF250/EFi250 2140
DD 630 external and internal 3 x EF250/EFi250 2540
DD 840 external and internal 4 x EF250/EFi250 3280
DD 500 external 2 x HD250 2140
DD 750 external 3 x HD250 2540


DDSTAT commercial controller

DDSTAT commercial controller

Ducted Gas Heating Service Centre

Ducted Gas Heating Service Centre
Operating 5 days a week, 8am to 5pm, Monday to Friday our New Zealand based customer service centre provides nothing but top quality. If you need to book in a Ducted Gas Heating service, we have a team of providers fully trained and equipped with diagnostic tools to service your appliance when you need them. 

Architects Portal

*Architects* Portal

Are you an Architect, Designer or Specifier?

We have everything you need to support your design process including CAD & BIM content. Check out everything you need from one easy Architects and Designers portal.

Enquire about a product

We’re happy to help with anything, big or small. Please fill out the short form below and we’ll get back to you within 24 hours.

Please enter your name Please enter your email address Please enter a subject Please enter a message

Where to Buy

Find a Rinnai reseller near you: