Installation Day for a New Furnace, Step by Step

What happens before the crew arrives?

The visit should be confirmed in writing with a start window and the model being installed. Clear the area around the furnace, move stored items back from the door and make sure pets are out of the way. If the furnace is in a finished basement, protect the route the crew will carry the old unit along.

Plan for the house to be without heat for several hours, so choose a day that is not the coldest of the week and have a space heater plan if you have young children or elderly relatives. The quote you accepted should be on hand to compare against what shows up.

How is the old furnace removed and the new one set?

1. Gas and power are shut off and the gas line is capped or disconnected.
2. The old furnace, flue and condensate lines are disconnected and carried out.
3. The new furnace is levelled, connected to the supply and return plenums and sealed to the ductwork.
4. Venting is run to code, including any intake pipe and a condensate drain on high-efficiency units.
5. The gas line is reconnected and tested for leaks, usually with a soap solution or an electronic detector.
6. Electrical and thermostat wiring are completed.

Be wary of rushed sealing at the ducts. Leaky connections at the plenum waste heat and can pull dust or combustion gases into circulation.

What should the crew test before leaving?

Commissioning is the part that separates a careful installer from a quick one. Ask to see or hear about these checks.

• Gas pressure at the manifold, matched to the unit's rating plate.
• Combustion analysis, with measured results written down.
• Temperature rise across the furnace, compared with the manufacturer's allowed range.
• Airflow and static pressure, so the blower is not fighting undersized ducts.
• Safety controls such as limit switches, flame sensor and pressure switches.
• Condensate drainage, with water run through the line.
• A carbon monoxide check near the furnace and at the vent outlet.

If the house was inspected for sizing, see why heat loss calculations matter. The same principle applies to a furnace.

What papers and instructions should you receive?

Before the crew leaves, you should have the model and serial numbers, the warranty registration steps, the permit number or inspection date, the filter size and replacement schedule, a thermostat walkthrough and the contact for after-hours problems. Registration deadlines for extended warranties can be short, so ask who registers the unit and get proof.

Keep the commissioning readings. They are a baseline for future service, which is why a proper annual tune-up compares new readings to the old ones.

What should you do in the first week?

Watch for unusual smells, short cycling, uneven rooms or loud blower noise. Check the condensate line for leaks. Confirm the carbon monoxide alarms in sleeping areas have fresh batteries. Report any issue in writing while the installer remembers the job. If an inspection is pending, do not assume it happened; ask for the confirmation.

Before your first winter with it, run through the winter home energy checklist for the rest of the house.

What can go wrong on the day?

Surprises happen even on well-planned jobs. Rotted plenum sheet metal, an old gas shutoff valve that will not seal, a vent route blocked by a beam or a chimney in worse shape than expected are all common. A good crew stops, shows you the problem and gives a written price for the fix before continuing, rather than adding it to the bill afterward.

Know in advance what you will do if the work cannot finish by evening. Ask whether the crew can leave a temporary heat source, and whether the old furnace stays disconnected or is returned to service overnight. Unfinished jobs left running without a final safety test are a risk, so insist on a completed test before the house is heated again.

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