In short
- Most gas furnaces made since 3 July 2019 must reach 95% AFUE under Canada's federal efficiency rules.
- A condensing furnace vents through plastic pipe out a side wall and drains its condensate to a floor drain or a pump.
- One Ottawa firm's published list puts a 95% single-stage furnace at $3,500–$5,000 installed and a modulating 98%+ unit at $5,500–$7,500+.
- A water heater left alone in the old chimney may need a metal liner, NRCan says.
Typical prices in Ottawa
| Job | Typical range | Notes |
|---|---|---|
| High-efficiency furnace, installed | $4,000–$6,750+ | Canada-wide HomeStars guide |
| Gas furnace, 95% AFUE, single-stage, installed | $3,500–$5,000 | One Ottawa firm’s published list, February 2026 |
| Gas furnace, 96–98% AFUE, installed | $5,000–$7,500 | Same firm’s list |
| Modulating gas furnace, 98%+ AFUE, installed | $5,500–$7,500+ | Same firm’s list |
| Venting change, chimney to side wall | $200–$500 | Same firm’s list |
| Condensate drain installation | $100–$300 | Same firm’s list |
Sources. HomeStars, Furnace Replacement Cost, Canada-wide, updated 21.08.2026, seen 29.10.2026. One Ottawa firm’s published list: Furnace Installation Cost Ottawa: 2026 Pricing, published 23.02.2026, HST not stated, seen 29.10.2026. Rules and technical facts: NRCan, Gas furnaces (Energy Efficiency Regulations), NRCan, Heating with Gas (PDF), TSSA and Enbridge Gas on snow-blocked vents, TSSA, registered and certified professionals, ESA, electrical inspections brochure (PDF), Ontario, guide for home renovation businesses, Home Renovation Savings, all seen 29.10.2026.
What “high-efficiency” means on a Canadian furnace
AFUE, Annual Fuel Utilization Efficiency, is the share of the gas that ends up as heat over a season. NRCan’s booklet Heating with Gas puts mid-efficiency power-vented furnaces at 78–84% and condensing furnaces at 90–98%.
Since 3 July 2019, federal rules require 95% AFUE from most gas furnaces of 225,000 Btu/h or less, with lower minimums for a few types. So a basic new gas furnace in an Ottawa quote is already a condensing unit. What moves the price is the burner, the blower and the work around the furnace.
Single-stage, two-stage, modulating
A single-stage burner has one output. A two-stage burner has two, and a modulating one adjusts across a range. NRCan says multi-stage furnaces run quieter with more even heat, and that most use a brushless DC blower.
On one Ottawa firm’s published list (February 2026), a 95% single-stage furnace runs $3,500–$5,000 installed, a 96–98% furnace $5,000–$7,500, and a modulating 98%+ unit $5,500–$7,500 and up. HomeStars’ Canada-wide guide puts a high-efficiency furnace at $4,000–$6,750 and up. Full job costs: furnace replacement cost.
The same firm notes a variable-speed blower can need a dedicated circuit. In Ontario, ESA says hired electrical work must be done by a Licensed Electrical Contractor, with a notification of work filed with ESA.
Two plastic pipes through the wall
The exhaust of a condensing furnace is cool enough to leave through approved plastic pipe, out a side wall. NRCan says most are certified for a two-pipe, sealed-combustion setup: one pipe brings outside air to the burner, the other carries exhaust out. The furnace then draws no air from the house, so the dryer and bath fans cannot pull on it.
The appliance’s instructions and the gas code set the clearances. Ask where the pipes will exit and what sits near that spot: a window, a deck, the gas meter, a path where snow gets piled. TSSA and Enbridge Gas say exhaust vents can sit as low as one foot above the ground and get buried by snow, which can let carbon monoxide build up indoors. In an Ottawa winter, that exit point is worth a minute on the call.
The water heater left in the chimney
In many older houses, the furnace and a gas water heater share one chimney. Once the furnace vents through the wall, the water heater is alone in a flue sized for two. A US Department of Energy workshop calls this an “orphaned water heater” and warns of carbon monoxide concerns from the oversized vent.
NRCan gives two routes. Keep the water heater on the chimney with an approved metal liner, which shrinks the flue so gases rise faster and condense less. Or replace the water heater as well, with a model that vents without a chimney. One Ottawa firm lists a chimney-to-side-wall venting change at $200–$500. For a rented water heater, see rent or buy.
Where the condensate goes
Condensing makes water. NRCan says it is piped to a floor drain or a condensate pump, and one Ottawa firm lists drain installation at $100–$300. Settle three points at the quote: distance to a floor drain, whether the line crosses a finished room, and whether a pump is needed. Put the drain’s location in your request.
Sizing and what the quote should list
NRCan says the size should come from a heat loss calculation under CSA standard F280, and calls sizing by floor area alone, or by matching the old furnace, inadequate in most cases. Ask to see the calculation.
A written quote should name the model, its AFUE and staging, and list separately: removal of the old furnace, PVC venting, the condensate line or pump, the gas connection, duct changes, water heater venting, electrical work, the thermostat, permits and HST. Ontario requires a written agreement for home renovation work over $50, and the final bill can go at most 10% above an estimate in it unless you sign a change. Gas work is for a TSSA-registered contractor employing certified gas technicians.
The Home Renovation Savings rebate list skips gas furnaces. A heat pump beside the furnace can qualify; see hybrid heating and furnace replacement.
Who handles your request
Ottawa Heating Desk passes your request to one independent heating company in the Ottawa area. That company calls you back, looks at the house, quotes the furnace and installs it.
Questions to ask the company
- What AFUE is the model, and is it single-stage, two-stage or modulating?
- Where will the two PVC pipes leave the house, and how high above the ground?
- Where does the condensate go, and is a pump on the quote?
- How will the water heater vent once the furnace leaves the chimney?
- Can I see the heat loss calculation, and the total with HST in a written contract?
Have this ready for the call
- A photo of the furnace label with the model and year
- Where it vents now: into the chimney, or pipes through a wall
- Whether a gas water heater shares that chimney, and whether it is owned or rented
- Where the nearest floor drain is, and whether the basement is finished
- The wall where pipes could exit, and any deck, window or gas meter near it
Questions people ask
Is 98% AFUE worth the extra over 95%?
One Ottawa firm’s published list says 98% models cost $1,000 to $2,000 more upfront and estimates the yearly gas saving over 95% at $50 to $100 for a typical Ottawa home. Ask the company for figures based on your house and your gas use.
What does a variable-speed blower change?
NRCan says a brushless DC (ECM) blower motor can cut the furnace’s electricity use by more than 70% when the fan runs continuously, which matters most in a house that keeps the fan on.
My furnace and water heater share a chimney. What happens to the water heater?
NRCan says it may need an approved metal liner, double-walled B-vent or stainless steel, to keep using the chimney. Its other route is replacing both with equipment that vents without a chimney. Ask for both prices.
Do the white pipes outside need anything in winter?
TSSA and Enbridge Gas warn that exhaust vents can sit as low as one foot above the ground and get covered by snow, letting carbon monoxide build up indoors. Keep snow from being blown or shovelled against them.
Is there a rebate for a new high-efficiency furnace?
The Home Renovation Savings site, seen 29.10.2026, lists heat pumps, insulation, windows and doors, smart thermostats and solar. A gas furnace alone is absent from it.
