What this covers
A furnace installation replaces the heat source for a forced-air system. The installer sizes the furnace from a load calculation, chooses a single-stage, two-stage or modulating unit and the efficiency the home and fuel suit, and removes the old furnace. The new unit is set level on a platform or pad, connected to the supply and return plenums with sealed sheet metal transitions, vented to the outside in metal or PVC as its efficiency requires, and tied to the gas line, the electrical circuit and a condensate drain. The company then fires it, checks gas pressure, temperature rise and combustion, verifies the safety controls, and shows you the filter and the thermostat.
When to call
- A furnace older than fifteen to twenty years that needs a repair each winter.
- A cracked heat exchanger found during service.
- Rooms that never warm up, or a blower that cycles on and off constantly.
- A furnace that stood in floodwater, or one damaged by fire or smoke, that is being rebuilt.
What to expect
- Size and selectThe load calculation and the existing ducts, fuel and venting path decide the furnace and its efficiency.
- Remove and setThe old furnace is disconnected and removed, and the new one set level and connected to the plenums.
- Connect and ventVenting, gas, electrical and condensate connections are made and leak checked.
- Start upThe furnace is fired, gas pressure, temperature rise and safety controls are checked, and the inspection arranged.
Get a certified company
Look up a certified company by ZIP code. Every company's license, insurance and trades are verified before it is listed, and placement is never paid.
Questions people ask
What efficiency should I choose?
Higher-efficiency condensing furnaces draw more heat from the same fuel and vent in PVC; standard-efficiency units vent in metal. The climate, the fuel and how long you expect to stay guide the choice, and the company explains the trade-offs.
Why does the new furnace need a drain?
A condensing furnace cools the exhaust until water vapor condenses out of it, and that water has to go to a floor drain or a small condensate pump.
Is an inspection required?
Where the local code requires a permit for a furnace replacement, the company pulls it and the work is inspected, including the gas connection and the venting.
Related: Furnace repair · Ductwork installation and repair · Gas line installation · All heating, cooling and air quality
This page describes what the service involves. The company you hire sets the scope, the schedule and the price, and your contract is with that company. We verify credentials and collect reviews from real jobs. We do not guarantee any company's workmanship. Safety steps are general guidance. When in doubt, leave the home and call 911.