Rinnai makes gas tankless water heaters. Units from 2009 onward start with two letters: a year letter beginning with A for 2009 and a month letter. Units from 1999 to 2008 start with the year and month as digits, sometimes with a period between them.
The first letter is the year, starting with A for 2009 (I, Q, U and V are not used). The second letter is the month.
BL.CA-051306 reads as November 2010.
Two sources agree Building Intelligence Center, Parts Town, Fast Water Heater Co., McGarry and Madsen Home Inspection, Blind & Sons, Rinnai training document
The first two digits are the year and the next two are the month. Some labels put a period between them.
04.03-102521 reads as March 2004.
Two sources agree Building Intelligence Center, InspectAPedia, Parts Town, McGarry and Madsen Home Inspection
A gas tankless water heater usually lasts 15 to 20 years, and sometimes longer, because there is no tank to rust through. Scale buildup in the heat exchanger is what shortens its life.
How long does a tankless water heater last? · Should I replace my water heater? · DC Dept. of Energy & Environment, U.S. DOE Building America
A.O. Smith · American Water Heater · U.S. Craftmaster · Bradford White · State · Reliance · Kenmore · Whirlpool · Rheem · Ruud · Richmond · GE · Marathon · Navien · Noritz · Takagi · Bosch (tankless water heater) · Lochinvar · GSW / John Wood · Paloma · HTP / Westinghouse / American Standard (water heaters) · Giant · EcoSmart / Eemax · Stiebel Eltron
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