Lochinvar 40 gallon gas water heater
Ser # DB877331
Model# LTN040G
Thanks in advance 
Try contacting them.
Not knowing about them, if I had to guess I would say 1987
**
**Lochinvar - Same as Bradford-White.
Bradford-White - They use a 20-year cycle. They skip the letters I, O, Q, R, U, V to make the full cycle.
1st Letter is the year. 2nd letter is the month.
A=84 B=85 C=86 D=87 E=88 F=89 G=90 H=91 J=92 K=93 L= 4 M=95
N=96 P=97 S=98 T=99 W=00 X=01 Y=02 Z=03 A=04 B=05 C=06 D=07
Thanks guys
Here is a cheat sheet for bradford-white and clones.