Furnace Installation from a Licensed Silicon Valley HVAC Contractor
Equipment selection starts with the AFUE decision. An 80% AFUE furnace (Goodman GM9S80, Rheem R801S, Carrier Comfort 80) costs $5,800-$8,200 installed for a typical 80,000 BTU residential model and uses an atmospheric or induced-draft B-vent up the original flue. A 95-98% AFUE condensing furnace (Carrier Infinity 59MN7, Trane S9V2-VS, Lennox SLP99V) costs $7,800-$11,500 installed and requires PVC sidewall venting, a condensate disposal path, and often a panel slot for the variable-speed ECM blower. In Bay Area homes the 95% unit pays back in 8-12 years on natural gas savings; in homes scheduled for solar + electrification within a decade, an 80% unit may be the rational choice. We model both scenarios in writing.
The venting transition is the trickiest part of a high-efficiency install. The original B-vent is now orphaned and must be either abandoned (capped at the appliance and roof) or resized for any remaining atmospheric appliances like a water heater — California Mechanical Code §802 requires a chimney liner sizing recalculation when the furnace is removed from a shared vent. New PVC venting must follow manufacturer concentric or two-pipe instructions: total equivalent length, slope (1/4-inch per foot back to the unit for condensate drainage), termination clearances (12 inches minimum from grade, 4 feet from any operable opening per California Plumbing Code 906.7), and freeze protection where applicable. We have run vent through Eichler tar-and-gravel roofs in Greenmeadow and shaved an extra cleanout port into a 1972 Willow Glen ranch crawlspace — every job is different.
Gas line sizing is the part most installers screw up. A 1990 home plumbed for a 100,000 BTU furnace may have a 1/2-inch black iron line running 40 feet from the meter — adequate for the original load but undersized for a modern 80,000 BTU furnace plus an 80,000 BTU tankless water heater added in 2015. We measure existing pipe, check pressure with a manometer at all appliances under load, and reference NFPA 54 (CA Plumbing Code Chapter 12) sizing tables. Often the fix is a partial 3/4-inch upsize from the meter to a tee that splits to the appliances — $400-$1,200 added to the project but it prevents brownout firing that destroys gas valves over time.
Combustion commissioning is non-optional and skipped by 70% of cheap installers. Once the furnace is running, we connect a Bacharach Fyrite InTech analyzer to a freshly drilled flue port (or the manufacturer's test port on condensing units), measure flue temperature, oxygen, CO, and CO2, calculate excess air and combustion efficiency, then adjust gas pressure at the valve to manufacturer spec (typically 3.5 inches W.C. on natural gas, 10 inches on propane). Target CO is under 100 ppm air-free; we routinely tune Bay Area installs to under 25 ppm. Final readings go on the invoice and on a sticker affixed to the furnace cabinet for the next tech who opens it. Title 24 HERS verification is scheduled within 14 days for qualifying installs.
What's Included in Every Furnace Installation Job
- ACCA Manual J load calculation matched to your home, not square-footage rule of thumb
- Removal and proper disposal of old furnace and combustion air openings
- New PVC vent or B-vent system per manufacturer and CA Mechanical Code
- Gas line sizing verification per NFPA 54 / California Plumbing Code
- Condensate disposal: pump, indirect waste, or gravity drain per code
- Combustion analysis with Bacharach analyzer and gas pressure adjustment to spec
- CO testing in living space and at supply registers
- Building permit pulled and inspection scheduled with your jurisdiction
- Title 24 documentation and HERS verification coordination if required
- 10-year manufacturer parts warranty and 2-year labor warranty
Common Furnace Installation Issues We Resolve
Existing furnace is 18+ years old and pilot-light era
Cause: Standing pilots, single-stage, atmospheric combustion at 65-72% AFUE
Fix: Replacement with 95% AFUE condensing or heat pump conversion; IRA 25C credit up to $600 for furnace, $2,000 for heat pump
Furnace shares a chimney with the water heater (orphaned vent risk)
Cause: High-efficiency furnace replacement removes the heat that drives water heater draft
Fix: Chimney liner downsize per CMC §802, or convert water heater to power-vent or heat pump tankless
Gas line undersized for current connected load
Cause: Original 1/2-inch line plumbed before tankless water heater or pool heater additions
Fix: Partial line upsize to 3/4-inch from meter; $400-$1,200
No condensate disposal path for high-efficiency unit
Cause: Garage or attic install without nearby drain, no exterior wall for gravity
Fix: Condensate pump (Little Giant VCMA-15ULS or similar) into laundry standpipe or exterior wall; $250-$550
Closet too small for new furnace clearances
Cause: Modern condensing furnaces require 1-inch side clearance, 24-inch front service, vent routing space
Fix: Closet enlargement or relocate to garage/attic; varies
Our Furnace Installation Process
In-Home Estimate
Free 60-90 min visit: load calc, vent path inspection, gas line measurement, combustion air verification, electrical panel review.
Written Proposal
Three equipment tiers (typically 80% AFUE entry, 95% AFUE mid, 96-98% AFUE variable-speed premium), itemized adders, rebate documentation, financing options.
Permits Pulled
Mechanical permit through your jurisdiction (Palo Alto Building Dept, San Mateo County, San Jose, etc.). Lead time 3-7 business days typically.
Installation
One day for most equipment swaps, two days if vent routing or gas line work involved. Floor protection, refrigerant recovery on combo units, full tear-out and rebuild.
Commissioning + Inspection
Combustion analysis, gas pressure adjustment, CO testing, thermostat configuration, walkthrough. Building inspector visit scheduled within 7-14 days.
Furnace Installation Pricing in the Bay Area
Typical furnace installation pricing in our Silicon Valley service area runs $5 800 – $11 500 installed. Most jobs complete in 1-2 days for installation; permit close-out 2-4 weeks.
Every quote is flat-rate and provided in writing before work begins. Diagnostic fees are waived when repair is approved. We never use time-and-materials billing surprise pricing.
Local Context: Furnace Installation in Silicon Valley
Bay Area heating loads are modest by national standards — most homes need 50,000-90,000 BTU output for a 1,800-2,800 sqft home in Climate Zones 3 and 4. That smaller load makes 95% AFUE less impactful in absolute dollar savings than it would be in Minnesota, but California Title 24 Part 6 still mandates HERS verification on new installations affecting duct leakage. Local gas utility PG&E charges G-1 residential rates with a tier system; tier 1 baseline allowances are seasonally higher in winter. Many older Eichler homes in Palo Alto, Sunnyvale, Mountain View, and Cupertino do not have forced-air heating at all — they use radiant slab boilers (typically Weil-McLain CGS or Lochinvar Knight WB) and we install hydronic equipment separately. Newer construction in Mission San Jose, Evergreen, and Cupertino almost universally uses 95% AFUE condensing furnaces; 1960s-1980s tract homes in Sunnyvale and Santa Clara still run 80% atmospheric units that we replace at the rate of 8-12 per week during October-December.
HVAC Brands We Service for Furnace Installation
Furnace Installation FAQ
Should I install an 80% AFUE or 95% AFUE furnace?
On a typical Bay Area gas usage of 350-500 therms per year, a 95% AFUE saves about $80-$140 annually over an 80% AFUE at PG&E G-1 rates. Payback on the $2,000-$3,500 price difference is 14-25 years — long. The 95% wins on clean combustion (PVC sidewall vent, no roof penetration, lower CO output) and on resale value in zip codes 94301-94306 where buyers expect modern equipment. The 80% wins if you are planning solar + heat pump conversion within 8 years and want minimum capital outlay.
Why does a high-efficiency furnace need a drain?
A 95% AFUE condensing furnace extracts so much heat from the flue gas that water vapor in the combustion products condenses back to liquid inside the secondary heat exchanger. That condensate is mildly acidic (pH 3-5) and runs about 0.7-1.5 gallons per hour during full firing. It must drain via gravity or pump to an indirect waste — never directly into a copper or cast iron drain (the acid eats them). We typically use a Little Giant VCMA-15ULS pump and discharge into the laundry standpipe or through the exterior wall.
Can I keep my old chimney for venting?
For an 80% AFUE replacement: usually yes, after a chimney liner inspection and possible resize per California Mechanical Code §802. For a 95% AFUE replacement: no, never — the flue temperature is too low (110-130°F) to maintain draft up a masonry chimney and condensate would saturate the liner. The 95% installs always use 2-inch or 3-inch PVC sidewall vent. If you have a shared vent with a water heater, removing the furnace will orphan the water heater and require its own remediation.
How long does a furnace installation take?
Standard 80% AFUE replacement in an existing closet with no gas line or vent changes: 6-8 hours, single day. 95% AFUE replacement with new PVC vent routing through wall or roof: 8-12 hours, sometimes spilling to a half-day on day two for finish work. Gas line upsizing or condensate path complications add 4-8 hours. We give a written estimated duration before the install and stick to it within an hour.
Do I need a permit?
Yes, every Bay Area jurisdiction requires a mechanical permit for furnace replacement. We pull the permit, schedule the inspection, and handle Title 24 paperwork. Skipping the permit creates real problems: voids manufacturer warranty, requires retroactive permits on resale (often more expensive than the original), and can void homeowner insurance on any related damage. A few small contractors offer "no permit" pricing — that is a red flag.
What about heat pump as an alternative to furnace replacement?
Strongly worth considering. A ducted heat pump (Carrier 38MURA, Trane XV20i Heat Pump, Mitsubishi Hyper-Heat MXZ-SM48NAMHZ) replaces both furnace AND AC, qualifies for $2,000 federal IRA 25C credit + $1,000-$3,000 TECH Clean California rebate + PG&E rebates + your CCA (SVCE or PCE) rebate. Stacking these typically reaches $4,500-$7,500 in incentives. Total project runs $14,000-$24,000 installed but net cost after rebates often beats a high-efficiency furnace + new AC combo.
Will a new furnace work with my existing thermostat?
Single-stage 80% units work with any thermostat. Two-stage 95% units need a thermostat with W2 terminal (most smart thermostats including Nest, Ecobee, Honeywell T9). Variable-speed modulating furnaces (Carrier Infinity, Trane TruComfort, Lennox iComfort) require the brand-specific communicating thermostat to access full modulation — using a generic thermostat works but reverts the furnace to two-stage operation.