There are multiple reasons why existing and new furnaces are often over sized. In the old days, houses lost

huge amounts of heat and were drafty due to air leaks in the building structure. If a heating contractor was not

equipped with enough information or lack experience and knowledge to perform a proper heat load calculation, they would

 recommend a larger furnace to be sure that it would provide sufficient heat under any weather condition. Few

people complain when their furnace can provide more than enough heat, but almost everyone complains when their

furnace cannot provide enough heat.

Renovations and upgrades made to older homes can dramatically improve their energy performance. For many

years furnace manufacturers did not keep up with improvements in the housing  and, therefore, did not make

small enough furnaces to meet the requirements of these better quality built houses.

With a proper heat load calculation, contractors are able to determine the appropriate size when recommending a

new or replacement furnace. Also sizing