Replacing Your Furnace/ Furnace sizing

There are usually two major reasons why you are choosing another forced-air furnace. The first is that your furnace does not function. It has just broken down, irrevocably, or it has been "red-tagged" or condemned by gas inspectors.

If it is winter, and your house is getting colder quickly, you may not have the luxury of making a reasoned choice on what to buy next. The other situation is that your furnace is getting old, or your fuel bills are becoming too excessive to tolerate.

In this case, you have the time to shop around and get the best furnace and fuel for your situation.

This About Your House is written to address both situations. If you have a dead furnace and a chilly house, you will probably take some shortcuts in your selection process.

Furnace Sizing

You probably do not need a furnace with the output of your current furnace. Most furnaces in Canadian houses can provide far more heat than the house requires. A properly sized furnace will be running almost continuously during the coldest day of the winter.

Having a furnace of a correct size will result in efficient operation during the whole heating season. A grossly oversized furnace will run only for a short period, never coming up to peak efficiency. Note, however, that sizing may not be a big issue with high-efficiency, condensing gas furnaces. Due to the design of condensing appliances, they are efficient even when oversized.

So, how do you size your furnace? You can have the contractor use a home heat loss calculation that is available from Canadian Standards Association (CAN/CSA F280) or a sizing procedure from the Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI). Having a proper sizing will cost you $150 - $300 from a qualified contractor.