Surface heat flux estimates from widely used atmospheric reanalyses differ locally by 10–30 W m−2 even in time mean. Here a method is presented to help identify the errors causing these differences and to reduce these errors by exploiting hydrographic observations and the resulting temperature increments produced by an ocean reanalysis. The method is applied to improve the climatological monthly net surface heat fluxes from three atmospheric reanalyses: MERRA‐2, ERA‐Interim, and JRA‐55, during an 8 year test period 2007–2014. The results show that the time mean error, as evaluated by consistency with the ocean heat budget, is reduced to less than ±5 W m−2 over much of the subtropical and midlatitude ocean. For the global ocean, after all the corrections have been made, the 8 year mean global net surface heat imbalance has been reduced to 3.4 W m−2. A method is also presented to quantify the uncertainty in the heat flux estimates by repeating the procedure with many different atmospheric reanalyses and then examining the resulting spread in estimates. This reevaluation of net surface flux reveals, among other results, that the Southern Ocean is a source of heat to the atmosphere.