HBV can be sexually transmitted. So it is prudent to vaccinate your wife (unless she has already developed immunity through previous exposure to HBV ) if you have chronic Hepatitis B. If in doubt, do a HBV serology test.
Generally, a person with very low viral load (hbvdna) also has low infectivity. It is not unusual for one HBV partner not infecting the other partner in a sexual relation. Best to have a blood test for both of you, then decide whether vaccination is needed.