Gas Furnace

Below is a typical illustration of high efficiency furnace system. It's great to be familiar with the terms in this diagram

• The blower in the bottom of furnace pushes air through Plenum and Supply Duct to every room then back from Return Duct and Boot into furnace

• High efficiency furnace can be vented through a side wall via PVC piping

Main features to be considered when buying a furnace:

1. Efficiency

• Higher efficiency models save heating costs and are worth the extra initial investment.

• In Canada, all furnace on market must be high efficiency (92% or above).

2. Heating capacity

• Ideally, a heat loss calculation should be performed in order to determine the heating capacity of the furnace. However, in most cases, the homeowner can’t provide the necessary detailed information such as building materials of the whole house. For this reason, it’s normally very difficult to accurately project heat loss.

• Taking a reference from your existing furnace is good way to determine what heating capacity you’ll need from your new furnace. Check the heating output of your existing furnace (remove the front panel of the furnace and you’ll find a label with all important data of your furnace like serial number, model number, input BTU and output BTU) and choose a furnace with a similar heating capacity.

3. Blower

The blower plays a very important role in heating and cooling system. The blower pushes air inside the ductwork and distributes energy to rooms inside the house. It is not only used by the furnace but also by the air conditioner.

• The best blower type is variable speed (also called DC motor). This type of blower can increase or decrease speed based on airflow needed. It’s quieter and more efficient on hydro consumption. It provides better air circulation. In the summer, it helps the central air conditioner achieve higher efficiency and better dehumidification.

• The second level is a multi speed blower which can create airflow in a few different speeds.

• Regular is fixed speed blower. It’s either on or off regardless of weather conditions.   

4. Burner stage

The heat needed inside the house is not a constant and it varies depending on the weather. For example, in order to keep temperature in house at 25 degrees, if outside temperature is minus 15, it might need burner to produce 80,000 BTU per hour. If the temperature outside is minus 2, it might need 50,000 BTU. If outside temperature is 5 degree, it might only need burner to produce 35,000 BTU

• The best type is modulating burner which can increase heating output incrementally so it has ability to produce heat to best match weather condition.

• The second-best type is two stage burner which can provide heating output either 60% or 100% of its heating capacity.

• Single stage burners don’t have any flexibility in terms of heat output. It’s either on or off regardless of weather conditions.

Factors related installation:

1. Venting

• New furnace will be vented by two PVC pipes through side wall. One pipe is for fresh air intake and another pipe is for exhaust.

• Vent terminal on outside wall has to be 3 feet away from gas meter and 12" away from the opening like window or door.

2. Draining of condensation water

• High efficiency furnace will make condensation water while in use.

• Condensation water comes out from bottom of furnace. It can easily run to floor drain. Or if there is no floor drain around, a condensation pump should be installed to get rid of the condensation water.

Further factors to be considered

1. Air cleaner

• It's installed between furnace and return duct.

• It cleans air and provides protection for furnace heat exchanger and air conditioner coil

2. Insulation of house

• Regardless of how high the furnace efficiency is or how good the blower is, the insulation of the house plays the most important role in terms of energy consumption.

• If house insulation is poor, it can't retain the heat therefore furnace is more frequently called in and works for a longer period of time. It not only increases energy consumption but also shortens the lifespan of furnace.

• If upgrading insulation of the entire house is not possible, to upgrade insulation in the attic is always the most cost-effective way to reduce heating expenses.

3. Rebate

• There usually are some rebates available from different sources. For example, Ontario Power Authority offer $250 rebate for furnace replacement if the new high efficiency furnace has EMC motor

• OPA rebate link

• Enbridge Community Energy Conservation Program offers up to $2000 rebate for certain area. Check here to see if you qualify.

4. Warranty

• Nowadays, most brands offer very generous warranty terms. 10 years on parts and lifetime on heat exchange are normal in the marketplace today.

• Labor warranty usually is provided by contractor who installs furnace. One year is typical term.