How Long Does a Furnace Replacement Take?

A straight furnace replacement, a new furnace going in where the old one was with the same type of venting, is usually a one-day job. Lennox's guide to installation time says most furnace installs are finished in a single day and puts the typical job at 4 to 10 hours. What pushes it longer is everything around the furnace: new venting, a chimney liner for the water heater, gas line changes, duct rework, and the permit inspection that comes afterward.

So the useful question isn't just how long, it's which of those your house needs. A good written quote tells you before install day.

The baseline: a like-for-like swap

Lennox, in a guide published November 24, 2025, breaks the time down by job:

A typical install day runs in this order: protect the floors and path, shut off gas and power, disconnect and remove the old furnace, set the new one, connect the ductwork transitions, gas piping, venting, condensate drain and wiring, then start it up, check gas pressure and temperature rise, set the blower speeds and walk you through the thermostat and filter.

Lennox also lists what adds hours: a larger or more advanced unit, ductwork that needs repair or resizing, tight access, add-ons like a new thermostat, filter cabinet or humidifier, and cold or snowy weather. Minnesota adds a few of its own.

What makes a furnace installation take longer in Minnesota?

Changing from an 80% to a 90%+ furnace. An 80% furnace vents up a metal flue into the chimney. A condensing 90%+ furnace vents through PVC pipe out a side wall or the roof, needs a condensate drain, and on direct-vent models a second PVC pipe for combustion air. Running two pipes through a finished basement and out the rim joist, with the terminations placed where drifting snow won't bury them, is real work. Our post on 96% vs 98% AFUE furnaces covers the efficiency side.

The water heater left behind. When the furnace leaves the chimney, a gas water heater that shared it can end up alone in a flue sized for two appliances. That can mean installing a chimney liner, or another venting fix, on the same job. It's one of the most common reasons a furnace swap in an older Minneapolis or Saint Paul house takes longer than planned.

Gas piping. A new furnace may need its gas connection moved, resized or brought up to current practice, such as a proper shutoff and sediment trap at the appliance. A longer run is a bigger job. HomeGuide puts a typical national range for a gas line run to an appliance at $350–$2,000, and our gas line guide explains when it comes up.

Ductwork. New furnaces rarely match the old cabinet's footprint, so the supply and return transitions get rebuilt on almost every job. Adding return air to a starved system, common on houses converted from gravity heat, adds more.

Access. Crawlspaces, attic furnaces, tight closets and narrow basement stairs all add time. So does a heavy old furnace that has to come out in pieces.

Old insulation. In pre-war houses, duct or pipe wrap may need to be tested for asbestos before anyone cuts it. If it tests positive, abatement comes first, and that is a separate contractor and a separate day.

Do Minneapolis and Saint Paul require a furnace permit?

Replacing a furnace needs a permit in both cities, and the installing contractor normally pulls it before work starts. Saint Paul's Department of Safety and Inspections says furnace and AC installations need a Warm Air/Ventilation/General Sheet Metal permit and a Mechanical permit, on top of an electrical permit. Our guide to HVAC permits in Minneapolis and Saint Paul goes through both cities, who issues what, and what the inspector looks at.

The inspection doesn't hold up your heat. Saint Paul's page describes arranging the final inspection once the installation is complete and the system is operational. In practice the furnace runs from install day, and the inspector visits on a later day. If the inspector flags something, the installer comes back to correct it.

How do you stay warm on furnace install day in winter?

Most of the day the heat is off only while the old furnace is out and the new one is being connected. A few things make that easier:

• Warm the house first. Turn the thermostat up a few degrees the night before and that morning, so the house has heat stored in it.
• Close the drapes and keep exterior doors shut as much as the crew's trips allow. Ask them to keep the door closed between loads.
• Use space heaters carefully, plugged straight into a wall outlet and away from anything that burns, and only where someone is in the room.
• Know the plan for the water heater. The gas is shut off during the swap, so the water heater may be off for part of the day too. The installer should relight and check it before leaving.
• Protect the pipes on a long job. If the work runs into a second day in deep cold, open the cabinet doors under sinks on outside walls.

What to have ready

1. A clear path from the door to the furnace, and a few feet of open floor around it.
2. A shoveled walk and driveway space for the truck in winter.
3. Pets closed in a room away from the open doors.
4. The outside wall where the vents will go cleared of snow, if you're switching to PVC venting.
5. Working CO alarms. Minnesota law requires them within 10 feet of every sleeping room, and a furnace swap is a good time to test them.
6. Time at the end to see the system run, learn the thermostat, find the filter and ask about warranty registration.

How we schedule a replacement

Before install day we size the furnace with a Manual J load calculation, not by copying the old nameplate, and give you a written quote that lists the venting, gas, duct and water heater work and the permit, so the time estimate is based on your house. A furnace replacement with us runs $4,500–$9,500 installed; our furnace replacement cost guide explains what moves it. Installs carry our 2-year labor warranty on top of the manufacturer's parts warranty.

For furnace installation in Minneapolis or Saint Paul, or anywhere within about 50 miles, we're open 7 days, 7am–9pm. Call 612-429-3465, and if your old furnace has already quit, tell us: no-heat calls get priority.

Questions

Sources

• HomeGuide cost guides (2026 editions) homeguide.com