When it's time for furnace replacement
Replace a furnace when its heat exchanger is cracked, when it's around 20 years old and needs a major part, or when repairs are coming every season and the house still isn't comfortable.
- Cracked or rusted-through heat exchanger. This is a safety failure, because combustion gases can mix with the air going into the house. On most furnaces the repair costs close to as much as a new unit.
- Age. Gas furnaces commonly last 15 to 25 years. Past about 20, a failed inducer motor, control board, or gas valve is worth weighing against replacement.
- Repeated repairs. Ignitors, pressure switches, and limit trips several winters in a row usually point to a furnace near the end of its life.
- Carbon monoxide readings or soot around the burners that cleaning and adjustment don't fix.
- Comfort problems: uneven rooms, long cold starts, or a blower so loud you hear it everywhere. Newer 2-stage and variable-speed furnaces fix much of this.
- The AC is being replaced too. The furnace blower moves the air for the air conditioner, so replacing both at once gives a matched system and saves a second round of labor and permits.
Choosing a new furnace: efficiency, staging, and size
80% vs 90%+ condensing furnaces
An 80% furnace vents hot exhaust up a metal flue. A condensing furnace (90% to 98%) pulls so much heat out of the exhaust that it cools enough to condense, so it vents through PVC pipe and needs a condensate drain. In colder climates the higher-efficiency furnace pays for itself fairly quickly.
In Santa Rosa, where the furnace runs only a few months a year, the gas savings are smaller, and the extra venting and drain work can matter more to the total cost. It's worth running the numbers for your house rather than assuming the highest number is the right choice.
Single-stage, 2-stage, and modulating furnaces
A single-stage furnace is either fully on or off. A 2-stage furnace runs on low most of the time, which gives quieter, longer, more even heating cycles.
A modulating furnace adjusts in small steps. Pairing a 2-stage or modulating furnace with a variable-speed blower also helps the air conditioner, because the same blower moves the cooling air.
Furnace sizing with a Manual J load calculation
Many older Santa Rosa furnaces are oversized for the house, especially in homes that have since added insulation or new windows. An oversized furnace heats in short, noisy blasts and wears out faster. The right size comes from a heat loss calculation (Manual J) for your house as it is today.
How furnace installation works
- Home visit. Load calculation, duct and return check, gas line and venting review, and a look at the electrical supply and the space where the furnace sits.
- Options and quote. Efficiency, staging, and whether a heat pump or dual-fuel system makes sense, with the permit and testing spelled out.
- Permit. A mechanical permit from the City of Santa Rosa.
- Removal. Gas and power are shut off, and the old furnace is disconnected and hauled away.
- Installation. The new furnace is set, the plenum and return transitions are fit, and the gas connection, venting, condensate drain (on condensing models), filter rack, and thermostat wiring are installed.
- Startup and combustion check. Gas pressure, temperature rise, combustion and CO readings, safety switch tests, and blower speed set for heating and cooling airflow.
- HERS verification and final inspection. Duct leakage and airflow testing where required, then the City inspection.
Venting and water heater issues when you switch furnace types
In many older homes, an 80% furnace and a gas water heater share one flue or masonry chimney. If the new furnace is a condensing model vented through PVC, the water heater is left alone in a flue sized for 2 appliances. That can keep it from drafting properly and spill exhaust into the house.
The fix is a properly sized liner or new vent for the water heater, and it belongs in the quote. Ask about it if your water heater is near the furnace.
The Bay Area zero-NOx furnace rule and your replacement decision
Most of Santa Rosa sits inside the Bay Area Air District, which regulates air quality for the southern part of Sonoma County. In 2023 the Air District amended its appliance rules so that, starting in 2029, new furnaces sold and installed in the district must be zero-NOx. In practice, that means electric heat pumps instead of gas furnaces.
As adopted, the rule applies to new installations. It doesn't require you to remove a gas furnace that's working.
What this means for you:
- A gas furnace installed now can be used and repaired for its normal life. It's likely the last gas furnace that house will get.
- If your furnace is 15 years old or more, compare a new gas furnace against a heat pump now, while you have a choice and time to plan.
- Electrical capacity is the long-lead item for a future heat pump. If your panel is small, knowing that now lets you plan an upgrade instead of being forced into it during a no-heat emergency.
- Dual fuel (a heat pump with a gas furnace as backup) is a middle step some owners take when the AC is due but the furnace is still fairly new.
Rule dates and details can change, and the northern edge of the Santa Rosa area falls under a different air district. Check the current Air District rule for your address before deciding.
What affects new furnace cost
Furnace replacement cost depends on efficiency and staging, the venting and gas work the new furnace needs, where it's installed, and what else changes with it.
- Efficiency: 80% versus a 90%+ condensing furnace, including PVC venting and a condensate drain or pump.
- Staging and blower: single-stage, 2-stage, or modulating, with a standard or variable-speed blower.
- Location: a garage or closet install is simpler than an attic or crawlspace install.
- Venting changes: new vent routes, roof or wall penetrations, and a water heater liner if needed.
- Gas line: resizing or a new shutoff and sediment trap to meet code.
- Ducts and return: new transitions, a larger return, or duct sealing to pass HERS testing. See ductwork repair.
- Permit, HERS testing, and haul-away.
No heat while you wait for a new furnace
If a technician shuts the furnace off for a cracked heat exchanger or a CO problem, it stays off. Don't restart it. How fast a replacement can be scheduled depends on equipment availability, so ask when you call.
Meanwhile, use electric space heaters safely: plugged straight into the wall, 3 feet from anything that burns, and never left running in an empty room. If someone in the house is very young, elderly, or ill, tell us when you call, because that changes how urgent the job is. For a no-heat problem that might still be repairable, start with furnace repair.
After your new furnace is installed
Register the furnace with the manufacturer to activate any extended parts warranty, and keep the permit and HERS paperwork. Change the filter on schedule. A media filter cabinet installed with the furnace lasts much longer between changes.
Book a fall tune-up each year. A new thermostat set up for 2-stage or variable-speed equipment gets the most out of it.
Furnace replacement is one part of the furnace and AC service in Santa Rosa HVAC Pros provides, from repair through installation.
Furnace replacement FAQs
How long does furnace replacement take?
A simple swap in a garage or closet is usually a 1-day job. Attic installations, venting changes, or a switch from 80% to condensing can add time. The HERS test and City inspection follow after installation.
Is a 96% furnace worth it in Santa Rosa?
Sometimes. Santa Rosa's short heating season means a high-efficiency furnace saves less gas here than in colder places.
It makes the most sense when the venting is easy to run and you plan to stay in the home a long time. When the venting is complicated, an 80% furnace or a heat pump can be the better value.
Can I still install a gas furnace in Santa Rosa?
Yes, for now. Under the Bay Area Air District's amended rule as adopted, new furnaces installed in the district starting in 2029 must be zero-NOx.
A gas furnace installed before then can be used and repaired for its normal life. Check the rule's current status, since dates can change.
Should I replace my AC at the same time as the furnace?
If the AC is over about 12 years old or uses R-22, usually yes. The furnace blower moves air for both, the indoor coil sits on the furnace, and one project means one permit and one round of testing. If the AC is newer, the new furnace can be set up to work with it.
Plan your furnace replacement in Santa Rosa
Call HVAC Pros at (707) 283-3186 to set up a home visit. We'll size the furnace, check the venting and ducts, and lay out gas and heat pump options side by side.