Rinnai RH180 Installation Fundamentals page 28

Vent Guidelines: Combustion air
When communicating directly with outdoors through
horizontal ducts, each opening shall have a minimum free
area of 1 square inch per 2000 Btu/hr (1100 mm
total input rating of all appliances in the confined space.
Note: If ducts are used, the cross sectional area of the duct
must be greater than or equal to the required free area of the
openings to which they are connected.
When communicating indirectly with the outdoors through
vertical ducts, each opening shall have a minimum free area
of 1 square inch/4,000 Btu/hr (550 mm
rating of all appliances in the confined space.
Combustion air to the appliance can be provided from a well
ventilated attic or crawl space.
Note: Check your local building codes to
ensure providing makeup air in the
manner you choose is allowed.
28
2
/kW) of
2
/kW) of total input