Nitrous acid (HONO) can be produced by heterogenous reactions of nitrogen dioxide on surface materials and direct emission from combustion sources. However, a little is known of indoor HONO levels or the relationship between residential HONO, NO, and $NO_2$ concentrations in occupied houses. Therefore, we measured simultaneously NO, $NO_2$, and HONO concentrations in living room of an apartment using continuous analyzers to study the production of HONO (June $22{sim}30$, 2006). The 4-min average concentrations of indoor NO, $NO_2$, and HONO were 4.3 (range: $0.4{sim}214.3$), 10.3 ($2.0{sim}87.3$), and 1.8 ppb ($0.3{sim}7.7$), respectively. Peak levels of HONO up to 7.7 ppb and 24-hr averages as high as 1.7 ppb were measured. In agreement with previous studies, indoor HONO concentrations increased during operation of an unvented gas range. Examination of the observed kinetics suggests that the secondary production of indoor HONO, possibly as a result of heterogeneous reactions involving $NO_2$ and $H_2O$ is associated with $[NO_2]^2[H_2O];(r^2=0.88)$ rather than with $[NO][NO_2][H_2O];(r^2=0.75)$. Three combustion experiments at nighttime were also carried out to investigate the effects of vented combustion on the HONO, NO, and $NO_2$ concentrations. It was found to release HONO for $10{sim}15$ minutes after NO and $NO_2$ source was turned off, and peak values were finally attained. Compared to unvented combustion, peak $NO_2$ and HONO concentrations were 3.2 and 2.0 times lower at weak vented combustion (air flow: $340;m^3/hr$) and 4.9 and 2.4 times lower at strong vented combustion (air flow: $540;m^3/hr$), respectively, emphasizing importance of operating ventilation hood fan during combustion to improve indoor air quality.