AFUE Explained Ontario 2026: What Furnace Efficiency Ratings Actually Mean

What AFUE Actually Measures

Annual Fuel Utilization Efficiency is the ratio of heat output to fuel input over a full heating season, expressed as a percentage. The US Department of Energy test procedure (adopted in Canada for ENERGY STAR certification) simulates steady-state combustion plus cycling losses, standby losses, and pilot-light losses where applicable, and rolls them into one annual number.[13]

The math is blunt. If your furnace is rated 96% AFUE and you burn $1,400 of natural gas over the winter, about $1,344 of that fuel ended up as heat inside your home and $56 went up the vent or was lost to cycling. If the same home had an 80% AFUE furnace, $1,120 ended up as heat and $280 was lost. The 16-point AFUE gap is worth about $224 a year at that usage level.[13]

Two things AFUE does not include. It does not account for duct leakage, envelope performance, or blower motor electricity. A 96% AFUE furnace pushing heated air through leaky attic ducts can deliver less usable heat than an 80% AFUE furnace in a tight system. That is why upgrading an older home's ductwork and sealing often pays back faster than chasing the last few points of AFUE. It also does not include electricity consumed by the blower motor, which is a separate spec (ECM variable-speed vs PSC fixed-speed) and shows up on your hydro bill, not your gas bill.[13]

The Three Tiers: 80%, 90%, 96-98%

Residential gas furnaces fall into three distinct efficiency tiers, each with different hardware. The jump from one tier to the next is not a tuning difference; it is a structural difference in how the furnace extracts heat from the combustion gases.[13]

80% AFUE: natural-draft, single heat exchanger

The 80% tier uses a single metal heat exchanger and vents hot combustion gases up a chimney or B-vent via natural draft. These were the industry standard from the 1980s through the early 2000s and are now largely obsolete in Ontario new construction. They are inexpensive ($2,000 to $3,000 installed) and compact, but you lose 20% of every fuel dollar up the chimney.[13]

In Ontario, 80% AFUE furnaces can no longer be installed in most new-build or major-renovation scenarios because of Building Code Section 9.36 and Supplementary Standard SB-12.[3] The one remaining use case is a like-for-like replacement in an older home with a chimney-vented system where retrofitting a condensing furnace is physically infeasible, and even those cases are increasingly rare as side-wall venting retrofits have become more common.

90-94% AFUE: condensing, single-stage burner

The 90% tier introduces a second heat exchanger (the condensing coil) that extracts additional heat from the water vapor in the combustion gases. Venting is via PVC or CPVC pipe out a side wall, not a chimney. Combustion gases are cool enough at exit that a B-vent is no longer safe or appropriate.[13]

This tier is rare in the Ontario market today because the 96% tier costs only slightly more and qualifies for rebates. You may still see 92% to 94% AFUE units in budget installs or in DIY-friendly model lines, but the mainstream market has moved to 96%+.

96-98% AFUE: condensing, staged or modulating

The 96% tier is now the mainstream Ontario install. It is condensing (side-wall vented), uses a secondary heat exchanger, and is available in single-stage, two-stage, and modulating burner configurations. AFUE ratings in this tier include:

• Carrier Infinity 98 modulating at 98.5% AFUE[6]
• Trane S9V2 two-stage at 96% AFUE and XC95m modulating at 97% AFUE[7]
• Lennox SLP99V modulating variable-capacity at 99% AFUE (highest in the market)[8]
• Napoleon 9500 single-stage at 95%, 9600 two-stage at 96%, 9700 two-stage at 97% AFUE[5]
• Goodman GMVM97 modulating variable-speed at 97% AFUE[9]
• KeepRite Ion 98 G97CMN modulating variable-speed at 98% AFUE[10]

Installed pricing in Ontario for 96% AFUE units runs $3,500 to $7,000 depending on brand and staging. Modulating 97% to 98% units add another $1,500 to $3,000 on top.[5][10]For the full cost range by brand, see our HVAC replacement cost guide for Ontario and our furnace brand ranking.

ENERGY STAR Canada Threshold (95% AFUE)

Many Ontario homeowners remember ENERGY STAR as a 90% or 92% AFUE threshold. That memory is out of date. Natural Resources Canada raised the ENERGY STAR gas furnace specification to Version 4.1 in 2023, and the current minimum is 95% AFUE for certified condensing gas furnaces with ECM blower motors.[1]

For Ontario rebate purposes, the practical threshold is even higher. The Enbridge Home Efficiency Rebate Plus program requires a minimum 96% AFUE for the furnace portion of the rebate stack.[4] That means a 95% AFUE ENERGY STAR certified furnace is still ENERGY STAR but will not qualify for the Enbridge rebate. A 96% AFUE ENERGY STAR furnace qualifies for both.

If a contractor's quote says "ENERGY STAR qualified" without specifying AFUE, ask them to write the AFUE number on the quote. Verify it against the AHRI Directory before signing.[12]

Ontario Building Code 9.36 Requirement (92%+ Minimum)

Ontario Building Code Section 9.36 (Energy Efficiency for Housing) is implemented through Supplementary Standard SB-12. SB-12 is the provincial prescriptive compliance document that sets minimum performance requirements for new housing and major renovations, including space-heating equipment.[2][3]

The SB-12 compliance tables set minimum AFUE at 92% in the base-level compliance packages, and many builder-selected compliance packages set the minimum at 94% or 96% to balance the rest of the envelope trade-offs.[3] The Peterborough SB-12 supplementary standard tables illustrate the pattern: Package A requires 96%, Package B requires 96%, Package C requires 94%, Package D requires 96%, Package E requires 94%, Package F requires 92%, and an HRV (heat recovery ventilator) is required across all packages.[3]

The practical consequence for Ontario homeowners is that almost every new-build furnace is 92% AFUE or higher by code, and most are 96% AFUE or higher because of the compliance-package arithmetic. Replacement installs in existing homes are also expected to meet SB-12 minimums in most jurisdictions, enforced at the permit stage.[3]

Modulating vs Two-Stage vs Single-Stage: Comfort Changes, AFUE Often Does Not

Burner staging is the number of heat-output levels the furnace can run at. It is independent of AFUE. Two 96% AFUE furnaces can have very different comfort profiles depending on how their burners stage.

Single-stage

One burner output: full on or full off. The furnace cycles: blast heat until the thermostat is satisfied, shut off, repeat. This is the cheapest option and the simplest to service. Ontario examples include the Trane XR95, Napoleon 9500, and Goodman GM9C96. AFUE ratings in this category run 95% to 96%.[7][5]The downsides are temperature swings (1 to 3 degrees between cycles), higher blower noise at full speed, and less effective humidity control and air filtration because run times are shorter.

Two-stage

Two burner outputs: low fire (typically 60% to 70% of full output) and high fire. The furnace modulates between the two based on outdoor temperature and call length. Ontario examples include the Trane S9V2, Napoleon 9600, Carrier Performance 96, and KeepRite G96VTN. AFUE ratings typically run 96% to 97%.[7][5]The comfort gain is real: run times extend by 30% to 50%, which means more filtration passes, better humidity pickup through the evaporator in cooling mode, and smaller temperature swings (0.5 to 1.5 degrees).

Modulating (variable-capacity)

Continuous modulation across a 40% to 100% output range in roughly 1% increments. The furnace matches output to heat demand in real time. Ontario examples include the Lennox SLP99V, Carrier Infinity 98, Trane XC95m, Goodman GMVM97, KeepRite Ion 98 G97CMN, and Napoleon 9700 Plus. AFUE ratings run 97% to 99%.[8][6][9][10]The comfort gain is substantial: temperature variance drops to under 0.5 degrees, blower noise at low fire is barely audible, and humidity management in shoulder seasons is notably better.

Why variable-speed blower does not change AFUE

AFUE is a combustion-plus-cycling metric. The blower motor does not enter the calculation. A variable-speed ECM blower saves electricity (up to 75% less than a fixed-speed PSC motor at low speed) and improves comfort, but the savings land on your hydro bill, not your gas bill, and are not reflected in the published AFUE number.[1][13]ENERGY STAR Canada Version 4.1 requires an ECM blower alongside the 95% AFUE threshold, so any ENERGY STAR certified Canadian furnace will already have the variable-speed blower included.[1]

Payback Math: When the AFUE Upgrade Is Worth It

The economics of upgrading efficiency tiers get unflattering as you climb. For an average Ontario home burning roughly $1,400 of natural gas a year at current Enbridge rates:

• 80% to 96%: $224 annual savings. Cost delta vs a like-for-like install is typically $1,000 to $1,500. Simple payback 5 to 7 years, excluding rebates. Worth doing.[13]
• 96% single-stage to 96% two-stage: $0 annual fuel savings (same AFUE). Cost delta $500 to $1,000. Pays off in comfort, not fuel. Often worth it for comfort alone.
• 96% two-stage to 97% modulating: about $14 annual savings. Cost delta $1,500 to $2,500. Simple payback 100+ years. Not worth it on fuel alone; only worth it if you specifically want the modulating comfort profile.
• 96% to 98% (premium modulating): about $28 annual savings. Cost delta $1,500 to $3,000. Simple payback 50+ years. Same logic as above.

Rebates change the arithmetic. The Enbridge Home Efficiency Rebate Plus pays up to $600 for a 96% AFUE furnace upgrade.[4] That alone can cut the effective cost delta of moving from 80% to 96% nearly in half. Rebates do not stack onto the tiny difference between 96% and 98%, so the payback math on the premium tier stays unflattering.

The one caveat to payback math is that moving from 80% to 96% also eliminates the chimney venting requirement, which can free up a chase or flue for other uses (re-lining, removal, or repurposing). That is a one-time value that does not show up in annual savings but can matter for renovations.

Real Ontario Furnace AFUE Ratings (2026 Models)

Below are representative AFUE ratings for furnace lines currently sold in Ontario. All are condensing units rated at or above the 96% rebate threshold unless noted otherwise. Prices are installed, equipment plus standard install labour, before rebates.

Two things to take from this table. First, AFUE does not track neatly with price. The Goodman GM9C96 at 96% AFUE installs for $2,800 to $3,800, while the Trane S9V2 at the same 96% AFUE installs for $5,500 to $7,500. You are not paying for extra efficiency at the higher price point; you are paying for brand, warranty, and staging comfort. Second, the premium Lennox SLP99V at 99% AFUE only buys you 1 AFUE point over the Carrier Infinity 98, which is statistical noise in real-world operation.

What to Ask on the Quote

When you get a furnace quote, make sure the following are on paper before you sign:

• Specific brand and model number (not just "Trane 96%"). Look it up on the AHRI Directory to verify the published AFUE.[12]
• AFUE rating in writing, at or above 96% for Enbridge rebate eligibility.[4]
• Staging type (single-stage, two-stage, or modulating). This affects comfort more than AFUE does.
• Blower motor type (ECM variable-speed, ECM constant-torque, or PSC). ECM variable-speed is required for ENERGY STAR and for proper operation of modulating stages.[1]
• ENERGY STAR certification confirmation (95% AFUE or higher under Version 4.1).[1]
• Confirmation that the install complies with Ontario Building Code 9.36 and SB-12 (usually via permit pull and inspection).[2][3]

If you are comparing AFUE numbers across quotes, read our SEER2 and HSPF2 ratings guide for the equivalent analysis on cooling and heat pump efficiency. The same principle applies: ratings are a starting filter, install quality is the real determinant of long-term performance.

Frequently Asked Questions