Residential wood smoke has received increasing attention as an important source of ambient particulate matter (PM2.5) that negatively impacts air quality and health. An investigation of the impact of ambient residential wood smoke emissions on indoor air quality was conducted in 32 residences, together with an evaluation of the effectiveness of electrostatic air cleaners (ESAC) at reducing indoor PM2.5 concentrations. Monitoring was conducted for 3 days in total. On day 1 the wood burning appliance operated as usual with no ESAC. On days 2 and 3 the wood burning appliance was not in operation. The ESAC was randomly chosen to operate in "filtration" or "placebo filtration" mode on day 2 and then switched on day 3. Twenty-one homes had valid infiltration efficiency estimates on the two days when indoor wood burning appliances were not in use. Average infiltration efficiencies were reduced from 0.49 (Std Dev = 0.29) to 0.29 (Std Dev = 0.20) when the air cleaner was in operation.