How Long Does it Take to Install a New Furnace?

Most furnace installations take 4 to 8 hours. A straight swap – pulling the old unit and dropping in a new one with existing ductwork – is usually done in a single day. Installations that involve new ductwork, a different furnace type, or a difficult location run longer, sometimes into a second day.

Here’s what actually drives the timing.

Standard furnace replacement: 4-8 hours

If you’re replacing an existing furnace with a similar model in the same location, this is the most common scenario. The technician removes the old unit, connects the new one to the existing duct system, gas line, and electrical, then runs startup and safety checks. For a well-prepared crew, this is comfortably a one-day job.

At North Wind, most of our furnace replacements in the GTA are completed same-day. We block the morning slot for furnace work specifically so homeowners aren’t left without heat overnight.

What makes an installation take longer

A few things regularly push a job past the one-day mark:

Ductwork modifications. If the new furnace is a different size or configuration than the old one, the duct connections need to be reworked. Minor modifications add an hour or two. Major ductwork – adding new runs, rerouting existing ducts, or upgrading an undersized system – can add a full day.

Fuel type conversion. Switching from oil to gas (common in Ontario as oil heat disappears) involves running a new gas line, capping the old oil tank, and often relocating the furnace. Plan for two days minimum.

First-time installation. If there’s no existing forced-air system in the home, ductwork needs to be installed from scratch. That’s typically a 2-3 day project depending on the house layout.

Difficult access. Attic installations, crawl spaces, or tight utility rooms all add time. Not much – maybe an extra hour or two – but it’s worth knowing upfront.

Permit and inspection requirements. Ontario requires a permit for new furnace installations. The permit application itself doesn’t delay the install, but some municipalities require an inspection before the furnace is used. Your contractor handles this – just ask about the timeline at booking.

Realistic installation timeline

What happens during a furnace installation

In roughly chronological order:

1. The old furnace is disconnected – gas line shut off, electrical capped, duct connections removed
2. The unit is removed from the mechanical room (this is usually the physically awkward part)
3. The new furnace is brought in and positioned
4. Gas line is connected and tested for leaks
5. Duct connections are made and sealed
6. Venting and combustion air are connected (this varies a lot by furnace type – standard vs high-efficiency)
7. Electrical connections are made
8. Thermostat is connected and configured
9. The system is started and run through a full heating cycle
10. Safety controls are tested (limit switches, pressure switches, rollout sensors)
11. Carbon monoxide detector is checked

The testing phase at the end isn’t something to rush. It’s where problems get caught before they become problems for you.

Can I stay home during the installation?

Yes. Most homeowners stay home. You’ll want someone there to sign off at the end anyway. The crew will need access to the mechanical room and ideally clear paths to bring equipment in and out. If you have pets, keeping them out of the work area helps.

Frequently asked questions about furnace installation time

How long does it take to install a new furnace?

Most furnace replacements in Ontario take 4 to 8 hours. If your home has existing ductwork and you’re doing a like-for-like replacement, one day is standard. More complex jobs – new ductwork, fuel conversions, difficult access – run into a second day.

Can a furnace be installed in one day?

Yes, in most cases. A standard furnace replacement with existing ductwork is a single-day job. Most contractors book the full day to give themselves time for thorough testing, but the physical work is often done in 5-6 hours.

How long does a high-efficiency furnace take to install?

About the same as a standard furnace – 4 to 8 hours for a replacement. The main difference is venting: high-efficiency (condensing) furnaces use PVC pipe venting rather than a metal flue, which sometimes requires running new vent lines to an exterior wall. If you’re replacing a standard furnace with a high-efficiency model, add an hour or two for the venting work.

What time of year is best to install a new furnace?

Late summer and early fall. Contractors are less slammed than they are in December and January when everyone’s furnace breaks in the same cold snap. You also have the luxury of choosing a convenient day rather than taking the first available emergency slot. The equipment selection and pricing are the same year-round.

Do I need a permit for a new furnace in Ontario?

Yes. Ontario requires a building permit for new furnace installations. Your contractor applies for it – you don’t need to do anything separately. The permit typically costs $150 to $300 depending on the municipality and is included in the installation quote from most contractors.

How long does a furnace last after installation?

15 to 20 years, if it’s maintained properly. Annual service – cleaning the burners and heat exchanger, checking the heat exchanger for cracks, inspecting the flue – is what gets you toward the 20-year end of that range. Neglected furnaces tend to fail earlier and less predictably.

Written by

James Kowalski

Senior HVAC Technician | G1 Gas Technician (TSSA)

James Kowalski is a senior HVAC technician with over 15 years of hands-on experience servicing residential and commercial heating systems across the Greater Toronto Area. Licensed by the Technical Standards and Safety Authority (TSSA) with a G1 Gas Technician designation, James specializes in complex furnace diagnostics, high-efficiency system installations, and emergency heating repairs. He holds HRAI certification and has trained dozens of junior technicians throughout his career.