How big should my furnace be??

Old 09-23-02, 07:42 AM
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Question How big should my furnace be??

I live in Toronto-Canada and have a 3000 square foot home with an 18 yearold furnace...

I am one of those shop-around consumers, so invited more than one vendor into my home to give me a quote.....however, they gave me quotes on furnaces ranging from 100,000 BTU to 125,00 BTU and I honestly don't know what size furnace will meet my family's needs.

I know that choosing the right sized furnace will be important for my home....since I know that there are a great many variables that need to be considered, I will give you as much info as I can about my home. (I apologize in advance for the long tale)

The original structure was Backsplit w/Brick Frame construction and approx 2000 sqft of living space with a partial basement and crawlspace for the balance of the foundation. The house faces West and gets a lot of sun. There are only 2 windows on the north side.

10 years ago a previous owner put a wood Frame addition on the house. This extended the kitchen on the main floor and put a second storey on the front of the house.

When the addition was built aother crawlspace/foundation was added and is the route for the new ducts (sadly, they did not build an access into the new crawlspace ) Immediately inside the crawlspace the large duct is divided into 4 smaller ducts to carry the heat/cooling up to the second floor.

Because the original structure is Brick Framed the architect took the liberty of designing an internal layout that has no walls on the groundfloor or second floor of the backplit lining up with one as my might expect, the duct work in the orginal part of the house is also an octopus of small 6"diameter conduit.

All of this ducting has lead us to the conclusion that we will not get enough benefit from a multi-stage furnace to warrant the expense...the blower running at reduced capacity sounds like it won't get anywhere with so many tributaries to feed. We have also decided that buying a mid-efficiency furnace and replacing old windows with better insulated ones is a better use of our available dollars than buying a high-efficiency furnace alone.

Our existing furnace is a Lennox G8E.

**********if i buy a 100K BTU Furnace, will the blower run more frequently than a 125K furnace? AND will that provide more even heating through my spaghetti ductwork? Can a 100K BTU furnace adequately heat my house at all?********

Any hint, tips or answers you can offer would be most appreciated....we are due for our first frost this weekend.


Old 09-23-02, 10:54 AM
Jacque Schidt
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You can download an evaluation copy of a load calc program and determine exactly what size your home needs. The one I use and like best is at The homeowner version is $40 US.

The smaller furnace you can abide with, the better your distribution will be. i.e., if the load calc says you need 102,000, get the 100,000, not the 125,000.

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