Replacing a furnace in San Leandro is usually about more than the box in the hall closet. The new unit should be sized for the heat your house actually loses on a cold night, vented in a way that suits its efficiency, and set up so the blower moves the right amount of air through your ducts. Most of the price, and most of the difference between a furnace that runs quietly for years and one that short-cycles, comes from those decisions.
Signs it is time to replace
- An old, inefficient furnace that still works but burns more gas than it needs to.
- Frequent repairs, especially when they are major parts such as the inducer, blower motor or control board.
- High heating bills without a change in how you use the heat.
- Uneven heating, with some rooms cold while the thermostat is satisfied.
- Safety concerns, above all a confirmed crack in the heat exchanger, which can let combustion gases mix with the air in your home.
If only one part has failed, read the furnace repair-or-replace guide first; a repair is often the better call.
80% or 90%+ efficiency
A furnace’s AFUE rating says how much of the fuel’s energy becomes heat in your home over a season.
| 80% AFUE furnace | 90%+ AFUE condensing furnace | |
|---|---|---|
| Gas use | Higher | Lower for the same heat |
| Venting | Metal vent, often shared with the water heater | Plastic pipes through a wall or the roof |
| Condensate drain | Not needed | Needed, with a drain route for the water |
| Installation work | Simpler when replacing a similar unit | More work when converting from an 80% unit |
Switching to a condensing furnace means a new vent route and a drain. If the old furnace shared its vent with the gas water heater, removing it can leave the water heater on a vent that is now too large, so that vent has to be checked and corrected as part of the job. In a climate where heating runs mostly from November to March, the gas savings of a condensing furnace are real but modest, and we show you both options with their installation costs side by side.
Sizing and airflow
Many furnaces in older homes are larger than the house needs. An oversized furnace heats in short bursts, cycles more often and leaves rooms uneven. The new unit should be sized from a load calculation that accounts for insulation, windows and air leakage. The blower matters as much as the burner: it has to match your ducts and, if you have central air, the cooling coil on top of the furnace. Variable-speed blowers run more quietly and spread heat more evenly.
Where the furnace sits
Furnaces here live in hall closets, garages, attics and under-floor crawlspaces, and each location changes the work. Closet units need enough combustion air and clearance. Attic and crawlspace units need horizontal equipment and safe access, and take longer to replace. Moving a furnace to a new location is possible, but it adds gas line, venting and duct work to the job.
What the installation includes
- Removal and disposal of the old furnace.
- Setting the new furnace and connecting the gas line, venting, ducts and electrical supply.
- A leak check of the gas connections.
- Startup checks: gas pressure, temperature rise across the furnace, venting draft and every safety control.
- Thermostat connection and a walk-through of the new system.
Replacing a furnace normally needs a permit and an inspection, and the estimate should list it.
What affects the price
Most furnace installations fall between $2,500 and $8,000, and the price depends mainly on system size and efficiency. A like-for-like 80% furnace in an open garage is at the low end. A condensing furnace with new venting and a drain, a variable-speed blower, an attic or crawlspace location, duct corrections or a water heater vent fix moves it up. You see the full price before work begins, financing is available, seniors and military households get 10% off, and we will beat any written quote. The equipment carries the manufacturer’s warranty; register it promptly, since some manufacturers require registration for the full parts coverage.
Furnace or heat pump?
If your air conditioner is also near the end of its life, a heat pump can replace both with one system, and in the mild local climate it handles most heating on its own. Some homes keep a new furnace as backup to a heat pump. We price the options side by side so you can compare.
Local notes
Most homes in San Leandro, San Lorenzo and Castro Valley were built with a gas furnace in a hall closet or garage and ducts in the attic or crawlspace. Those ducts are often decades old, so a new furnace is a good moment to have them checked; a duct repair can fix the cold bedroom that no furnace size would. A new thermostat set up for the new furnace makes the most of a variable-speed blower.