HomeShape AI — How-to guide
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HomeShape Repair Coach
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HVAC & Climate · Heating & Cooling Equipment
Furnace & Air Conditioner
Your HVAC system is the most expensive thing in your house you can't see — and the one most likely to fail at the worst possible moment. Regular filter changes and seasonal tune-ups are the cheapest insurance you'll ever buy.
All 9 zonesLifespan: 15–20 yrs (furnace/AC), 10–15 yrs (heat pump)Found in nearly all homesHVAC & Climate
Avg replacement cost
$6,500–$16,000
full furnace + AC system, installed
Emergency vs. planned
+10–15% or more
premium for rushed, unplanned replacement
Most common failure
Capacitor (AC) / dirty filter & igniter (furnace)
largely preventable with routine maintenance
DIY-able tasks
~60%
of routine maintenance
Something not working right?
Answer a few quick questions and get a personalized diagnosis from the HomeShape Repair Coach.
Select your type
Gas furnace — the most common central heating system in the US, burning natural gas or propane and pushing heated air through ductwork. Common brands: Carrier, Trane, Lennox, Goodman, Rheem, American Standard, Bryant. Typical lifespan 15–20 years with maintenance. It’s the one HVAC type where a maintenance lapse can be a life-safety issue (carbon monoxide), not just a cost issue.
Maintenance tasks
| Task | Cadence | Skill | Time | Consequence if skipped |
|---|---|---|---|---|
Replace or clean air filter Swap disposable filter or clean washable filter | Every 30–90 days (more with pets) | 1 · Beginner | 5 min | Restricted airflow, reduced efficiency, overheating, premature blower and heat-exchanger wear |
Clean burners Remove dust and soot buildup on the burner assembly | Annually | 2 · Confident | 30 min | Soot and condensation buildup accelerates aging and causes uneven, incomplete combustion |
Test and clean flame sensor Lightly sand the flame sensor rod's contact surface | Annually | 2 · Confident | 20 min | Burners ignite then shut down quickly (short cycling), eventually no heat at all |
Inspect heat exchanger for cracks Visual/mirror inspection for hairline cracks or rust-through | Annually (pro-recommended) | 3 · Advanced | 30–60 min | Safety hazard — a cracked heat exchanger can leak carbon monoxide into the supply air |
Inspect venting and flue pipe Check for rust, disconnected joints, and proper slope away from the unit | Annually | 2 · Confident | 15 min | Backdrafting sends combustion gases, including CO, into the home instead of outside |
Test or replace igniter Check hot-surface igniter glow and continuity | Every 5–7 yrs or as needed | 3 · Advanced | 45 min | No ignition means no heat — a leading cause of no-heat service calls |
Lubricate blower motor and inspect belt Oil motor bearings if applicable, check belt tension and wear | Annually | 2 · Confident | 20 min | Motor bearing wear, noisy operation, eventual motor failure |
Test carbon monoxide detectors near the unit Verify CO detectors near the furnace and bedrooms are functioning | Monthly test; replace unit every 5–10 yrs | 1 · Beginner | 5 min | Undetected CO leak — the single highest-stakes furnace safety failure |
Troubleshooting
Symptom
Likely cause
Action
Who
Pilot light or igniter won't stay lit
Faulty thermocouple or dirty/failing flame sensor
Clean the flame sensor with fine sandpaper first; replace the thermocouple or igniter if it persists
DIY ok
Blowing cold air
Thermostat set to "Cool" or fan set to "On" instead of "Auto", or a brief normal startup delay
Check the thermostat mode and fan setting; wait a few minutes for normal heat-up
DIY ok
Blower runs constantly with weak, cool airflow
Dirty filter or a malfunctioning fan limit switch
Replace the filter first; if unresolved, the limit switch needs professional replacement
Call pro
Short cycling — burners shut off quickly after lighting
Dirty flame sensor or overheating from restricted airflow
Clean the flame sensor and check the filter; persistent issues need professional diagnosis
Call pro
Gas smell near the unit
Gas leak at a fitting or valve
Leave the home immediately, call the gas company from outside, and don't operate any switches
Evacuate
Burning smell, unusual noises, or a CO alarm
Cracked heat exchanger or an electrical fault
Turn off the furnace immediately, confirm CO detectors, and call an HVAC professional
Evacuate
Recommended tools & materials
Heat pump — moves heat rather than generating it via combustion, making it 2–4x more efficient than resistance electric heat, and serves as both heating and cooling in one unit. Common brands: Carrier, Bryant, Trane, Mitsubishi, Daikin, Goodman, Rheem. Typical lifespan 10–15 years. No combustion, no flue, no CO risk — but it has an outdoor condensing unit and indoor coil like an AC, doubling the moving parts that need seasonal attention.
Maintenance tasks
| Task | Cadence | Skill | Time | Consequence if skipped |
|---|---|---|---|---|
Replace or clean air filter Same return-air filter as a furnace | Monthly check, replace as needed | 1 · Beginner | 5 min | Reduced airflow forces the system to work harder and cuts efficiency |
Clear outdoor unit debris Remove leaves, grass clippings, and snow within 18–24" of the unit | Monthly / after storms | 1 · Beginner | 10 min | Restricted airflow around the coils reduces heating and cooling capacity |
Clean condenser and evaporator coils Rinse outdoor coil fins with a hose, no pressure washer | Twice yearly, spring and fall | 2 · Confident | 30 min | Dirty coils reduce heat transfer efficiency and increase energy use |
Check refrigerant charge Verify correct refrigerant pressure in both heating and cooling modes | Twice yearly (pro task) | 3 · Advanced | 30–60 min | Refrigerant imbalance reduces capacity and risks compressor damage |
Inspect condensate drain Check for clogs or algae in the drain line | Annually | 2 · Confident | 15 min | Water backup, potential water damage, humidity and mold issues |
Verify defrost cycle operation Confirm the unit properly defrosts the outdoor coil in cold weather | Seasonally, cold climates | 2 · Confident | 10 min | Ice buildup on the outdoor coil blocks airflow and drastically cuts heating capacity |
Cycle the system in both modes Run heating and cooling modes to confirm both function | Twice yearly | 1 · Beginner | 10 min | A mode-specific failure goes unnoticed until the season you actually need it |
Troubleshooting
Symptom
Likely cause
Action
Who
Weak heat, house stays cold
Dirty filter, low refrigerant, or the unit stuck in defrost
Check and replace the filter first; if unresolved, needs a professional refrigerant check
Call pro
Ice buildup on outdoor unit that won't clear
Defrost cycle malfunction or blocked airflow
Clear debris and snow from the unit; if ice persists, the defrost control needs professional repair
Call pro
System defaults to expensive electric backup heat
A heat pump component fault, or the thermostat set to "Emergency Heat"
Check the thermostat mode first; if that's not it, get a professional diagnosis
Call pro
Outdoor unit not running at all
Tripped breaker, blown fuse, or a failed contactor/capacitor
Check the breaker and disconnect; if power is fine, the contactor or capacitor needs professional replacement
Call pro
Hissing or bubbling sound with reduced performance
Refrigerant leak
Don't attempt to recharge it yourself — refrigerant work requires EPA certification
Call pro
Recommended tools & materials
Central air conditioner — a split system with an outdoor condenser/compressor unit and an indoor evaporator coil, often paired with a separate gas furnace for heat. Common brands: Carrier, Trane, Lennox, Goodman, Rheem, American Standard, York. Typical lifespan 15–20 years. Unlike a heat pump, a straight AC only cools.
Maintenance tasks
| Task | Cadence | Skill | Time | Consequence if skipped |
|---|---|---|---|---|
Replace or clean air filter Same shared filter as the furnace/air handler | Every 30–90 days | 1 · Beginner | 5 min | A clean filter can cut cooling costs ~15%; a clogged one restricts airflow and can freeze the coil |
Clean condenser coils Rinse outdoor unit fins clear of dirt, pollen, and grass | Annually, spring | 2 · Confident | 30–45 min | Dirt on the coils reduces efficiency and stresses mechanical parts |
Clear debris and maintain clearance Keep 2 ft of clearance around the outdoor unit, trim vegetation | Monthly during cooling season | 1 · Beginner | 10 min | Restricted airflow reduces capacity and can overheat the compressor |
Clear condensate drain line Flush the drain line, e.g. with vinegar or a shop vac | Every 1–3 months in season | 2 · Confident | 15 min | A clogged drain causes water backup, overflow, and potential water damage |
Check refrigerant level Verify correct charge, inspect lines for leaks | Annually (pro task) | 3 · Advanced | 30–60 min | Low refrigerant reduces cooling capacity and can damage the compressor |
Test capacitor Check the start/run capacitor with a multimeter | Annually or at first sign of trouble | 3 · Advanced | 20 min | Capacitor failure is one of the most common AC repairs — causes hard-starting or total no-start |
Inspect electrical connections and disconnect Check wiring, tighten connections, verify the outdoor disconnect | Annually (pro task) | 3 · Advanced | 20 min | Loose connections risk arcing, overheating, and component failure |
Troubleshooting
Symptom
Likely cause
Action
Who
Not cooling, warm air from vents
Dirty filter, blocked outdoor coil, or low refrigerant
Check the filter and clear debris around the outdoor unit; if unresolved, it's likely a refrigerant leak needing a pro
Call pro
Won't turn on at all
Tripped breaker, thermostat issue, or a dead capacitor
Check the breaker and thermostat batteries/settings first; a failed capacitor needs professional replacement
Call pro
Ice forming on refrigerant lines or the indoor coil
Restricted airflow (dirty filter or blocked vents) or low refrigerant
Turn off the unit, let the ice melt, replace the filter; if it recurs, it's a refrigerant or airflow issue for a pro
Call pro
Water pooling near the indoor unit
Clogged condensate drain line
Clear the drain line with a shop vac or vinegar flush; if a pump has failed, call a pro
Call pro
Burning smell or electrical odor
Electrical fault or motor failure
Turn off the system immediately at the breaker and call an HVAC professional
Evacuate
Recommended tools & materials
Ductless mini-split — one or more wall/ceiling-mounted indoor units connected by refrigerant lines to a single outdoor compressor, used for room additions, older homes without ductwork, or zoned heating and cooling. Common brands: Mitsubishi Electric, Daikin, Fujitsu, LG, Carrier, MRCOOL. Typical lifespan 10–15 years, up to 20 with strong maintenance. The washable indoor filters need far more frequent attention than a central system’s disposable filter.
Maintenance tasks
| Task | Cadence | Skill | Time | Consequence if skipped |
|---|---|---|---|---|
Clean indoor mesh filters Remove and rinse the washable filters | Monthly | 1 · Beginner | 10 min | Reduced airflow, lower efficiency, and it can trigger error codes |
Clean indoor unit housing and vents Wipe down the exterior, dust intake and outlet vents | Every 2–3 months | 1 · Beginner | 10 min | Dust buildup restricts airflow and can circulate allergens |
Clear outdoor unit debris Remove leaves and vegetation within 18" of the outdoor compressor | Monthly / after storms | 1 · Beginner | 10 min | Restricted airflow reduces capacity and stresses the compressor |
Clean condensate drain and pan Clear the drain line, check for algae or clogs | Annually | 2 · Confident | 20 min | Water leaking from the indoor unit and potential mold growth |
Clean evaporator coil Gently clean the indoor coil behind the filter | Every 6 months | 2 · Confident | 30 min | Reduced heat transfer, ice buildup, mold or mildew odor from the unit |
Check refrigerant lines for leaks Inspect the line-set insulation and flare connections | Annually (pro task) | 3 · Advanced | 30 min | A refrigerant leak causes weak performance; EPA rules require certified handling to repair |
Schedule a professional tune-up Full coil clean, fan balance, refrigerant check | Twice yearly | 3 · Advanced | 1–2 hrs (pro) | Minor issues compound into major, costlier repairs |
Troubleshooting
Symptom
Likely cause
Action
Who
Not cooling or heating adequately
Dirty filter, or the unit is mismatched to the room size
Clean the filter first; if unresolved and sizing seems right, check for a refrigerant leak
Call pro
Water leaking from the indoor unit
Clogged condensate drain line or improper installation slope
Clear the drain line with a wet/dry vac; persistent leaking may need a professional slope or pump repair
Call pro
Ice on the outdoor coil during cold-weather heating
Unit running below its rated low-ambient temperature, or snow blocking airflow
Clear snow and debris from the outdoor unit; if it's a cold-climate design limit, consult the installer
Call pro
Flashing lights or a persistent error code
Communication or wiring fault between indoor and outdoor units, or a failed control board
Power-cycle the system; if the code persists, it needs professional diagnosis
Call pro
Weak performance despite a clean filter, sweating copper lines
Refrigerant leak
Don't attempt a DIY recharge — it requires an EPA-certified technician
Call pro
Recommended tools & materials
Relevant In Your Zone
The Deep Freezer
Your furnace carries a heavy load all winter long.
The Humid Hotbox
The A/C runs hard here, and humidity control depends on it working right.
The Dry Scorcher
Peak summer heat pushes cooling systems to their limit.
Related Guides
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