Choosing a new furnace for your home

Which fuel should a new furnace use?

The choice is usually between natural gas, electricity and oil, and in practice it is often made for you by what is already connected to the house. A gas furnace needs a gas service and a vent. An electric furnace needs no vent and is simple to install, but electric resistance heat gives one unit of heat per unit of electricity, so the running cost depends heavily on local rates. Oil furnaces need a tank and a chimney.

Fuel prices and the carbon cost of each fuel differ by province and change over time. The comparison in natural gas versus electric heating sets out the main trade-offs, and home heating costs in Alberta shows how one province looks in practice.

Before you commit to a furnace of any kind, ask whether a heat pump could do part or all of the job. A heat pump moves heat instead of making it, which is why it can beat both gas and electric resistance on running cost. The heat pump versus furnace guide explains when each wins.

How do you pick the right furnace size?

Furnace size means heating capacity, normally listed in BTU per hour on the data plate. It is not about how big the cabinet is. The right capacity matches the heat your house loses on a design cold day, which depends on insulation, windows, air leakage and the local climate. Square footage is a rough shortcut and it often points to a bigger furnace than the house needs.

Oversizing is common. An oversized furnace heats the house quickly, shuts off, then starts again soon after. That short cycling is noisy, wears parts and leaves rooms with swings in temperature. Houses that have had new windows, attic insulation or air sealing since the old furnace was installed are the usual victims.

Ask the contractor to base the quote on a heat loss calculation and to show you the result. Load calculations are described in a separate guide, and an energy audit can supply the air leakage data that improves the figure.

What does the efficiency rating mean?

Furnaces are rated by AFUE, annual fuel utilization efficiency. It shows what share of the fuel energy ends up as heat in the house across a heating season. The rest leaves through the flue. Condensing models, usually called high-efficiency, pull extra heat from the exhaust and are typically rated well above older mid-efficiency designs.

A worked example shows what the gap means. Suppose a house needs 100 units of heat over a winter. A furnace rated at 80 percent burns 125 units of fuel to deliver it. One rated at 96 percent burns about 104. The saving is roughly one-sixth of the fuel, which is meaningful in a cold climate, but its dollar value depends on the price of the fuel and the length of your season. Higher-efficiency units also cost more to buy and to vent, so the payback is a calculation to run with real quotes. Our comparison of a high-efficiency furnace and a heat pump looks at the same question.

Comfort features sit alongside AFUE. A two-stage or modulating burner and a variable-speed blower smooth out temperature swings and are often quieter.

What else belongs in a new furnace decision?

The furnace is one part of the heating system. Leaky or undersized ducts can cancel a good furnace, and the thermostat controls how well it runs. Ask the installer to check the ductwork and static pressure, and to price any repairs separately. Installation details, including venting and the permit, are covered in the furnace installation guide.

Read the warranty too. A longer parts warranty may need registration or a yearly service, so read the terms. A furnace that is serviced each year lasts longer, and the annual tune-up guide lists what a visit should cover.

Rebates exist for some heating equipment, but programs change and eligibility depends on the fuel, the province and the utility. Check the Government of Canada energy-efficiency pages and your provincial energy ministry before you sign, because some programs need pre-approval.

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