5 Mistakes to Avoid With Heating & Furnace

5 Mistakes to Avoid With Heating & Furnace

Most San Diego homeowners assume their furnace needs less attention because it only runs a few months each year. That assumption itself is the biggest mistake. Intermittent use is harder on certain components than continuous operation, and a furnace that sits idle from April through October faces unique thermal cycling stress when it fires up cold in November.

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If you’d rather have a Master Technician inspect your system before problems start, call Redwood Heating & Air San Diego at (844) 875-9451. Estimates are free.

Mistake 1: Skipping the Pre-Season Inspection Because “We Barely Used It Last Year”

This is the most expensive assumption we see in San Diego. A furnace that runs intermittently experiences more thermal cycling stress than one running steadily through a cold climate. Each cold start forces the heat exchanger to expand rapidly from room temperature to operating temperature, often 1,200°F or more. That repeated expansion and contraction creates metal fatigue at the weld points and curves.

The igniter suffers similar stress. Hot surface ignitors in modern furnaces are silicon carbide or silicon nitride elements that degrade with every heating cycle, not with total runtime hours. A San Diego furnace cycling on and off through 60 winter nights may accumulate more igniter wear than a Minneapolis furnace running continuously.

What we check in a pre-season inspection:

• Heat exchanger integrity via visual inspection and combustion analysis
• Igniter resistance and physical condition
• Flame sensor microamps and corrosion
• Gas valve manifold pressure
• Blower motor amp draw and capacitor tolerance

Last November we replaced a cracked heat exchanger in a Scripps Ranch home where the homeowner had skipped three consecutive years of inspections. The unit had low runtime hours but high cycle count, and the thermal fatigue was invisible until we pressure-tested it.

Mistake 2: Blocking Vents in Unused Rooms to “Save Energy”

Closing supply vents in guest bedrooms or offices seems logical. It isn’t. Modern furnaces with variable-speed blower motors are designed for specific static pressure ranges. Blocking vents raises system pressure, which forces the blower to work harder and can cause the heat exchanger to overheat.

Here’s what happens in a typical San Diego home with a 90% efficiency furnace and ECM blower motor. You close two bedroom vents. Static pressure rises from 0.5 inches water column to 0.8 or higher. The blower ramps up to maintain airflow, drawing more amps. The reduced air volume across the heat exchanger causes the high-limit switch to cycle the burner on and off repeatedly. That thermal cycling we mentioned earlier? You’ve just multiplied it.

The damage accumulates slowly. We’ve found heat exchangers with premature cracks in Clairemont homes where this practice went on for years. The homeowner never connected the guest room vent closure to the furnace failure.

If you have rooms you don’t use, ask us about zoned systems or duct modifications. Don’t choke your existing system and hope for the best.

Mistake 3: Ignoring the Flue and Combustion Air Pathway

San Diego’s mild climate means many furnaces live in garages, attics, or exterior closets that would be unthinkable in colder climates. These installations create specific combustion safety risks that annual inspection should catch.

Garage-installed furnaces face backdrafting risk when the garage is under negative pressure. Running a clothes dryer, kitchen exhaust, or even opening the house-to-garage door quickly can pull combustion gases backward through the draft inducer. California’s Title 24 building code requires specific clearance and combustion air provisions, but older San Diego homes often predate current standards.

A combustion analysis measures:

• Oxygen and carbon dioxide levels in flue gas
• Carbon monoxide concentration (should be under 100 ppm in flue, zero in living space)
• Draft pressure and spillage under worst-case depressurization
• Flame roll-out or burner flame impingement

Any furnace tune-up that doesn’t include a combustion analysis with printed or digital results is incomplete. We perform this on every heating inspection at Redwood Heating & Air, regardless of equipment age. A visual-only check misses what the analyzer catches.

Mistake 4: DIY Carbon Monoxide Detector Placement

California law requires CO detectors in single-family homes, but placement determines whether they actually protect you. We’ve seen detectors mounted exactly wrong: directly above the furnace where heat causes false alarms, or on the opposite end of the house from sleeping areas where they’d sound too late.

Effective placement for San Diego homes with furnace systems:

• One detector within 10 feet of each bedroom door, or inside each bedroom
• One detector on each level, including basements and habitable attics
• Minimum 15 feet from the furnace itself to avoid nuisance tripping from startup emissions
• Minimum 5 feet from fuel-burning appliances like water heaters
• Never in dead air spaces: corners, behind doors, inside cabinets

Hardwired interconnected detectors with battery backup provide the best protection. When one alarms, all alarm. If your home still has plug-in or battery-only units from a previous owner, consider upgrading. The 15-year lifespan matters too, older detectors lose sensor sensitivity even with fresh batteries.

We check detector placement and expiration dates during our heating inspections. It’s a two-minute check that belongs in every service call.

Mistake 5: Accepting a “Tune-Up” Without Combustion Testing and Heat Exchanger Inspection

The HVAC industry has a terminology problem. “Tune-up” means anything from a filter change and visual glance to a full diagnostic with printed combustion analysis. The price range in San Diego reflects this, from $49 specials to $200+ comprehensive inspections. The difference isn’t markup, it’s scope.

A legitimate furnace inspection for any brand, whether it’s a York, Daikin, Bryant, or American Standard system, should include:

• Heat exchanger visual inspection with mirror or borescope, plus pressure test if accessible
• Combustion analysis with digital readout of O2, CO, CO2, and flue temperature
• Gas pressure verification at manifold and inlet
• Blower assembly removal and cleaning if needed
• Electrical connection torque and amp draw on all motors
• Filter evaluation (not just replacement, but sizing and pressure drop assessment)
• Thermostat calibration and anticipator or cycle rate verification

The $49 special typically covers two items from that list. We’ve been called to San Diego homes where a “tune-up” was performed weeks before a failure that proper diagnosis would have caught.

At Redwood Heating & Air, Gregory Hahn founded this company and still leads every technical decision. Our inspections follow the same protocol whether we’re looking at a 30-year-old Goodman or a new American Standard modulating furnace. The brand changes, the standards don’t.

When to Call a Pro

Call before the first cold night if your furnace has sat unused since spring, if you smell any combustion odor on startup, if your CO detectors are over seven years old, or if your last “tune-up” didn’t produce printed diagnostic results. Heating & Furnace in San Diego service from Redwood Heating & Air includes full combustion analysis on every inspection.

Related services in San Diego: Heat Pump & Mini Split in San Diego for homes considering alternatives to furnace heating, or AC Repair & Installation in San Diego for year-round system coordination.

The Bottom Line

San Diego’s short heating season creates a false sense of security. The furnaces that fail most expensively here aren’t overworked, they’re neglected by owners who assumed low runtime meant low risk. Thermal cycling, static pressure damage from closed vents, combustion safety in garage installations, inadequate CO protection, and superficial “tune-ups” are all preventable with proper seasonal attention.

Key takeaways:

• Intermittent use causes thermal fatigue, not less wear
• Closing vents damages variable-speed blowers and heat exchangers
• Garage furnaces need combustion analysis for backdrafting risk
• CO detector placement matters as much as presence
• Demand printed combustion results from any “tune-up”

If you’re in San Diego and want your furnace inspected by a Master Technician who’ll show you the actual diagnostic numbers, Redwood Heating & Air San Diego offers free estimates. Call (844) 875-9451 or visit our Redwood Heating & Air San Diego home page to schedule.

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