A high-efficiency furnace saves a GTA household roughly $360–$450 a year on a $1,800 gas heating bill, which works out to $5,400–$6,750 over 15 years — often more than the upgrade itself costs. The saving comes from moving off an old mid-efficiency furnace that threw a fifth of its fuel up the chimney. If your current furnace is already condensing, the gain from a newer one is much smaller, and the honest answer is to keep the one you have.
What AFUE measures, and why 95% is now the floor
AFUE is Annual Fuel Utilization Efficiency: the share of the gas you buy that ends up as heat in the house over a full season. A 96% AFUE furnace turns 96 cents of every dollar into heat. Furnaces built in the 1980s and 1990s typically ran 60% to 80%, venting the rest as hot exhaust.
Canada's federal minimum for new residential gas furnaces is 95% AFUE, so every unit a contractor can legally install in your house today is a condensing furnace. That changes the shopping question completely. You are no longer choosing between efficiency classes — you are choosing how the furnace delivers its heat.
How much a high-efficiency furnace saves on a GTA gas bill
Take a Toronto home spending $1,800 a year on gas heat with a furnace in the 80% range. Moving to a 96% unit removes about a fifth of the fuel burn, which is $360–$450 a year at today's rates. Over 15 years that is $5,400–$6,750 in lower bills.
Two things widen or narrow that gap. A leaky, under-insulated house wastes the new furnace's output the same way it wasted the old one's, so the percentage holds but the dollars follow your envelope. And a thermostat left at one temperature 24 hours a day gives back part of the gain — if your bills feel high for the size of the house, work through why heating bills spike in winter before you buy equipment.
Where the rest of the saving hides: the blower, not the burner
The burner efficiency is the headline; the blower is where the second saving sits, and it shows up on the hydro bill rather than the gas bill. An older PSC blower motor draws the same power whether the furnace is on low fire or high. An ECM blower ramps, runs long and slow, and uses a fraction of that in circulation mode.
That is also the comfort difference people actually notice. Long, low-speed runs even out the temperature between the room above the furnace and the bedroom over the garage far better than a burner that blasts and quits.
Single-stage, two-stage or modulating: how the tiers compare
Free quotes, written pricing.
- Single-stage 96% with a constant-torque blower — one output level, lowest price, the sensible pick for a small bungalow or a rental property
- Two-stage 96% with a variable-speed ECM — runs on low fire most of the season, quieter, noticeably better at holding an even temperature upstairs
- Modulating 97%+ with a communicating thermostat — adjusts output in small increments, strongest in a three-storey or a split-level, and the tier that most rewards a well-balanced duct system
- Premium badge at any tier — Lennox SLP98V, Carrier Infinity 98, Trane S9V2 typically add $500–$1,500 over an equivalent value-brand unit at the same stage count
Money spent moving from single-stage to two-stage buys more real comfort than money spent moving from a value brand to a premium one at the same stage count. If the duct system is undersized on the return side, fix that before you buy a modulating furnace — it cannot modulate against a restriction.
What a condensing furnace needs that your old one did not
- PVC intake and exhaust instead of a chimney, terminated outside where snow will not drift over them — the north and west walls are where we find blocked terminations after a lake-effect storm
- A condensate trap and drain, because a condensing furnace produces acidic water every time it runs; the trap needs flushing at each annual service
- A condensate pump where the drain is above the furnace, which is common in older basements with no floor drain nearby
- Two-pipe direct venting in a tightly built house, so the burner draws combustion air from outside rather than from a sealed mechanical room
- A filter cabinet sized for the new blower — a 25 mm filter slot on a variable-speed furnace is a permanent restriction
Rebates on a high-efficiency furnace in Ontario right now
Ontario's live program is the Home Renovation Savings Program, delivered by Enbridge Gas with Save on Energy since January 2025. Furnace upgrades on their own typically land in the $500–$1,500 range, and a smart thermostat installed with the furnace qualifies for $75. Requirements change, so read the program page rather than a contractor's flyer — we keep the current picture on our Ontario rebates page.
Two programs are still quoted in the wild and both are finished: the Canada Greener Homes Grant stopped accepting new applicants in 2024, and Enbridge's Home Efficiency Rebate has wound up. The federal Oil to Heat Pump Affordability program is still running but only applies to homes heated with oil, which rules out almost every gas-heated house in the GTA.
Is the upgrade worth it if your furnace still runs?
- Mid-efficiency furnace venting into a chimney, 15 or more years old — yes, and the fuel saving does much of the work of paying for it
- Condensing furnace under 12 years old — no; you would be buying a stage count and a blower, not an efficiency jump
- Furnace of any age with a cracked heat exchanger — replace, and take the efficiency gain as a bonus rather than the reason
- Planning to sell within two years — replace only if the current unit is failing; the buyer's inspector cares more that it works and was permitted
- Adding air conditioning at the same time — do both at once and the sheet metal, the electrical and the permit only happen once
If you are seeing more than one of the warning signs that a furnace is finished, the efficiency question has already answered itself. And whatever you install, pair it with a decent control — the gains from a smart thermostat stack on top of the equipment, not instead of it.
ZK Mechanical installs and services high-efficiency heating systems across the GTA and Hamilton, with the venting, condensate and duct work quoted in writing before we start and the rebate paperwork filed for you. If you want the numbers run against your own gas bill rather than an average, send us your details and we will do the arithmetic with you.
Frequently asked questions
Is a 96% furnace worth it over a 95% one?
The one-point difference in AFUE is not worth choosing a furnace over — on a typical GTA gas bill it is a rounding error. What is worth paying for at the same efficiency is the blower and the staging: a two-stage furnace with a variable-speed ECM runs longer at lower output, uses less electricity to circulate air, and holds a steadier temperature between floors than a single-stage unit does.
How long does a high-efficiency furnace last?
Fifteen to 20 years in Ontario, with condensing models sitting toward the lower half of that range. The secondary heat exchanger, the trap and the drain line handle acidic condensate for the whole life of the unit, so they are the parts that decide the ending. An annual service that includes flushing the trap and checking the venting terminations is what keeps a condensing furnace at the top of the range.
Can I put a high-efficiency furnace in an older Toronto house?
Yes, and most of the ones we replace are in older houses. The work that gets added is venting — running PVC intake and exhaust out through a wall instead of up the chimney — and dealing with what the old furnace leaves behind. If your water heater shared that chimney, it will need the flue lined, because it is now venting alone into a passage sized for two appliances.
Do high-efficiency furnaces need more maintenance?
A little more, and it is specific rather than general. The condensate trap and drain need flushing annually or they block and shut the furnace down on a pressure switch fault. The PVC terminations outside need to stay clear of snow and leaves. Beyond that it is the same annual visit as any gas furnace: burners cleaned, flame sensor polished, and a combustion analysis at the flue.