es ▁from ▁the ▁fire box , ▁but ▁require ▁a ▁much ▁higher ▁temperature ▁for ▁the ▁secondary ▁comb ust ion . ▁No ▁catal yst ▁is ▁required . ▁ ▁These ▁models ▁lose ▁a ▁large ▁amount ▁of ▁efficiency ▁at ▁low ▁burn ▁rates , ▁as ▁they ▁cannot ▁maintain ▁secondary ▁comb ust ion , ▁but ▁can ▁be ▁very ▁efficient ▁at ▁higher ▁temper atures ▁that ▁allow ▁secondary ▁comb ust ion . ▁ ▁There ▁also ▁exist ▁hy brid ▁st ov es ▁that ▁employ ▁both ▁catal yt ic ▁and ▁non - catal yt ic ▁secondary ▁comb ust ion . ▁ ▁Sto ves ▁that ▁do ▁not ▁employ ▁any ▁secondary ▁comb ust ion ▁still ▁exist , ▁but ▁are ▁marked ly ▁less ▁efficient ▁than ▁a ▁modern ▁st ove ▁due ▁to ▁their ▁lack ▁of ▁secondary ▁comb ust ion . ▁ ▁Py ro ly zing ▁st ov es ▁In ▁a ▁conventional ▁st ove , ▁when ▁wood ▁is ▁added ▁to ▁a ▁hot ▁fire , ▁a ▁process ▁of ▁py ro ly s is ▁or ▁destruct ive ▁dist ill ation ▁begins . ▁G ases ▁( or ▁vol at iles ) ▁are ▁evol ved ▁which ▁are ▁burn ed ▁above ▁the ▁solid ▁fuel . ▁These ▁are ▁the ▁two ▁distinct ▁processes ▁going ▁on ▁in ▁most ▁solid ▁fuel ▁app li ances . ▁In ▁ob sole te ▁st ov es ▁without ▁secondary ▁comb ust ion , ▁air ▁had ▁to ▁be ▁admitted ▁both ▁below ▁and ▁above ▁the ▁fuel ▁to ▁attempt ▁to ▁increase ▁comb ust ion ▁and ▁efficiency . ▁The ▁correct ▁balance ▁was ▁difficult ▁to ▁achieve ▁in ▁practice , ▁and ▁many ▁ob sole te ▁wood - burn