Several years ago we suffered a nightmare of a poor installation of a
furnace. The new oil furnace needed better flow through the chimney
which we found later was partially blocked and we had to have it
cleared and lined.
Furnace also backfired and poor installation of a simple thing like
changing the filter replacement around left an unsealed vent and smoke
went from furnace room throughout house. We had to have the house
cleaned 3 times from the original cracked plenum and the chimney and
backfire problems of the poor installation. Took about a month to
straighten out the mess and insurance which installer had to pay.