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Furnace Buying Guide

When you schedule quotes with various heating contractors to buy a furnace, you can be sure most of them will present you with three different features, each of them costing you more.
These features are:

  • higher efficiency
  • two stage operation
  • variable speed fan motors.


Most major manufacturer's offer standard efficiency (80% AFUE), high efficiency (90% AFUE), and ultra high efficiency (about 95% AFUE) models. Most furnaces over 10 years old are only 60-70% efficient. The AFUE efficiency rating refers to the percentage of the heat that the furnace creates that enters your house instead of escaping up the chimney. Older furnaces let the exhaust gases leave the furnace at temperatures much higher than 212F so that they rise quickly and so that the water in them does not condense into a liquid and rust the heat exchanger and chimney. 80% efficient furnaces have a second fan motor that can push the exhaust up the chimney at temperatures just above 212F. 90-95% efficient furnaces have a second stainless steel heat exchanger where heat is removed from the exhaust gasses until the water condenses into a liquid. Plastic chimney pipes must then be installed running out of the house.

High efficiency models cost about 50% more than standard models, but the energy savings usually pay for this extra cost in less than 10 years. So, except for homes with lower than average heating costs, high efficiency is usually a good investment.

Two stage operation

One of the most common complaints people have about their heating systems is that they leave uneven temperatures throughout the house. Most older furnaces only have one setting: full blast. On mild days, they briefly fire up and blast out hot air when the thermostat calls for heat. They don't come on again until the house gets a little too cold. This results in inconsistent temperatures over time. Their lower amount of time in operation also results in uneven temperatures from room to room, leaving some corners of the house uncomfortably chilly. A two stage furnace which will run on a lower burner setting most of the time will help alleviate these problems. It will also be quieter most of the time when running in its lower setting. Expect to pay about 15% more for a double stage furnace than a single stage model.

Variable speed DC fan motors

A variable speed DC fan motor responds to various sensor inputs to provide the optimal airflow rate. This results in more precise control of heat delivery.

Some homeowners prefer to run their furnace's fan continuously throughout the day. The flow of air this creates throughout the home can create a mild cooling effect on summer days and, like having two burner stages, can also help create more even temperatures throughout the home. A variable speed motor uses much less power when it is being run continuously. A standard AC motor will use over 300 watts when gently circulating air through an average size home, while a variable speed DC motor will only use about 25 watts. This results in energy savings that can pay for the feature in a few years. Also, a variable speed motor will be very quiet when running on its lower settings. Expect to pay about 20% more for a variable speed model.

Choosing the right contractor

The best way to find a good contractor is always to find some people you know who have recently had heating systems replaced. If you know several people who can provide feedback on local contractors, then you're a lucky person. Distinguishing the good from the bad can otherwise be a difficult task.

If you live in a city that requires gas permits for installations and has inspectors check a large number of the installations, you're also in luck. Ensuring a quality installation is as simple as ensuring that your contractor buys a gas permit for the job.

Other measures you can take are to 1) contact your local Better Business Bureau to see if any complaints have been filed against the company 2) check for references 3) ask for proof of installer certifications and 4) search online for local contractor review sites. Unfortunately, you probably aren't going to do any of these things. Most people just wind up going with their gut, based on how professional the company appears. Some people go with more expensive larger companies for a lower chance of a poor installation. Some go with lower priced smaller contractors to try and save money.

Excessive worry probably isn't warranted, though. Furnace installations are not as complex as hot water heating system, heat pump, or AC installations. Even homeowners who go with lower priced contractors are fairly unlikely to run into major problems as a result of a poor furnace installation.

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Our thanks to:
Jack Gregson
HouseSmart Heating
Vancouver, Canada

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