Question: When the catalytic converter is used up (i.e. needs to be replaced) will the efficiency or the heat output of the stove be affected if the converter is not replaced ? Answer: ABSOLUTELY! The combustor will boost the overall efficiency from 55-60% to high 70's. If you don't burn the gases leaving the wood (accounts for 50% of usable heat), you are losing valuable heat up the chimney, increasing the potential of creosote development in the flue, wasting fuel, and polluting the environment. Replace the combustor when necessary. It's worth it.