A tank water heater typically lasts about 8 to 12 years, and sometimes up to 15 with good maintenance and soft water. Tankless water heaters often last around 20 years. Hard water, high temperature settings and skipped maintenance shorten lifespan. Because tank failures can cause water damage, it’s smart to plan a replacement once your tank passes 10 years.
Quick answers
Gas tank: about 8–12 years. Electric tank: about 10–15 years.
Tankless: about 20 years. Heat pump water heater: about 10–15 years.
Find the age in the serial number on the label.
Rusty water, leaks at the base and rumbling noises are warning signs.
Yearly flushing and anode rod checks help a tank last longer.
Lifespan by type
Type
Typical lifespan
Main reason it fails
Gas tank
8–12 years
Tank corrosion
Electric tank
10–15 years
Tank corrosion, element failures
Tankless (gas or electric)
~20 years
Heat exchanger scale, components
Heat pump (hybrid)
10–15 years
Tank corrosion, compressor/fan
How to find your water heater’s age
Look at the manufacturer’s label on the side of the tank. The manufacture date is often encoded in the serial number. Common formats use a letter for the month and two digits for the year, or the first four digits for year and week. Search for your brand plus “serial number date code” to decode it.
A failing tank can release dozens of gallons of water. If your heater is in an attic, finished basement or interior closet, replacing it proactively around year 10 to 12 can prevent costly water damage. Install a drain pan and a leak alarm under the new heater.
Frequently asked questions
Can a water heater last 20 years?
Tankless units often do. Tank heaters rarely do unless they have soft water, regular maintenance and anode replacements.
Does a water heater warranty indicate its lifespan?
Somewhat. Tank warranties are commonly 6, 9 or 12 years, reflecting differences in anode rods and construction.
If your AC runs constantly but the house won’t cool down, the system is either not removing enough heat or the house is gaining heat faster than the AC can remove it. Check airflow first (filter, vents, blower), then the outdoor unit, then the house itself (sun, attic, leaks). If the air at the vents isn’t noticeably cold, a refrigerant or compressor problem is likely.
Quick answers
Healthy systems usually deliver air about 15–20°F colder than the air going into the return.
Replace the filter and open all vents first.
Clean the outdoor condenser coil.
On very hot days, most ACs can only keep the house about 20°F below outdoor temperature.
Weak temperature drop at the vents usually means a refrigerant or compressor issue.
Test the temperature split
Use a simple kitchen or digital thermometer:
Measure the air at a return grille (where air goes into the system).
Measure the air at a supply vent close to the indoor unit after the AC runs 15 minutes.
Subtract.
Temperature difference
What it suggests
15–20°F
System is cooling properly; the house may be gaining heat too fast
10–14°F
Possible airflow, coil or charge problem
Under 10°F
Likely refrigerant, compressor or major airflow problem
If the outdoor coil is covered in dirt, cottonwood or grass, the system can’t reject heat. Rinse it with a hose (power off). How to Clean an AC Condenser Coil
3. Closed or blocked vents and returns
Rooms with closed vents stay warm and the rest of the system loses airflow. Open supply vents and keep returns clear of furniture and rugs.
4. Leaky ducts in the attic
Ducts that leak in a hot attic lose cooled air and pull in hot air. Signs include rooms far from the unit staying warm and dusty attic insulation near duct joints. Sealing with mastic or foil tape (not cloth duct tape) helps. A contractor can measure duct leakage.
5. Low refrigerant
A leak lowers cooling capacity gradually. You may notice the system runs longer every week. Ice on the lines and hissing are other signs. This requires a licensed technician. AC Refrigerant Recharge Cost
6. Failing compressor or capacitor
A weak run capacitor can let the compressor run inefficiently. A failing compressor may run hot and trip off. A technician can test both.
7. Too much sun and heat gain
The house itself can be the problem:
Close blinds and curtains on east windows in the morning and west windows in the afternoon.
Avoid using the oven and dryer during the hottest hours.
Check attic insulation. Many older homes have far less than the recommended level.
Make sure the attic is ventilated.
8. The system is undersized
If the house was expanded, or the original system was too small, it may never keep up on hot days. Compare your home’s square footage with the sizing chart in What Size AC Do I Need?
9. Thermostat placement or calibration
A thermostat in direct sun, near a lamp or by a kitchen reads too warm and runs the AC endlessly. Compare its reading with a separate thermometer. Move or recalibrate it if needed.
How to keep the house cooler during a heat wave
Pre-cool the house in the morning, then hold a steady setting.
Use ceiling fans in occupied rooms (counterclockwise in summer).
Keep doors to cooled rooms closed only if each room has a return or a gap under the door.
Avoid setting the thermostat extremely low: it won’t cool faster.
When to call a technician
If the temperature split is under 15°F with a clean filter and coil, call a professional. Ask them to check refrigerant charge, coil condition, blower speed and duct static pressure.
Frequently asked questions
Why does my AC cool at night but not during the day?
Heat gain is highest in the afternoon. A system that is marginally sized or slightly low on refrigerant shows it first on hot afternoons.
Should my AC run all day in extreme heat?
On the hottest days, long run times are normal. If it runs constantly on mild days, something is wrong.
Can a bad thermostat cause the house not to cool?
Yes, if it reads the wrong temperature or doesn’t call for cooling properly.
If your AC is blowing warm air, start with the three quickest checks: make sure the thermostat is set to COOL (not HEAT or FAN ON), replace a dirty air filter, and confirm the outdoor unit is running. Those three account for a large share of “warm air” calls. If the outdoor unit is silent or the air stays warm after 20 minutes, the problem is likely a tripped breaker, a failed capacitor, frozen coils or low refrigerant.
Quick answers
Thermostat on HEAT, AUTO changeover or FAN ON is the most common simple cause.
A clogged filter can starve the system of airflow and freeze the indoor coil.
If the outdoor fan isn’t spinning, check the breaker and the disconnect box first.
Ice on the copper lines means airflow or refrigerant problems. Turn cooling off and let it thaw.
Refrigerant problems and electrical part replacements are jobs for a licensed technician.
Before you start: stay safe
Turn the system off at the thermostat before touching anything. The outdoor unit has a disconnect box (usually a gray box mounted on the wall near the condenser). Pull the disconnect or switch off the breaker before opening any panel. Capacitors inside the outdoor unit can hold a dangerous electrical charge even with the power off, so never touch them unless you are trained.
1. The thermostat is on the wrong setting
Check three things on the thermostat:
Mode should be COOL.
Fan should be AUTO, not ON. With the fan set to ON, the blower keeps pushing air even when the compressor is off, and that air feels warm.
Set temperature should be at least 3 degrees below the room temperature.
A filter packed with dust restricts airflow over the indoor coil. Less airflow means the coil gets too cold, ice forms, and cooling drops. Pull the filter out and hold it up to a light. If you can’t see light through it, replace it. Most 1-inch filters need changing every 1 to 3 months during cooling season. Our guide: How Often Should You Change Your Air Filter?
3. A tripped breaker or blown disconnect fuse
Central air conditioners use two circuits: one for the indoor air handler or furnace and one for the outdoor condenser. If the indoor fan is blowing but the outdoor unit is silent, check the electrical panel for a tripped double-pole breaker labeled AC or condenser. Reset it once. If it trips again, stop and call a technician: repeated trips point to a shorted compressor, fan motor or wiring.
4. The outdoor unit is dirty or blocked
The condenser releases the heat taken out of your house. Grass clippings, cottonwood fluff, leaves and dryer lint on the fins act like a blanket. Keep at least 2 feet of clearance around the unit and rinse the fins gently with a garden hose from the inside out (power off). Step-by-step: How to Clean an AC Condenser Coil.
5. A failed capacitor
The capacitor gives the compressor and outdoor fan motor the jolt they need to start. When it fails, you’ll often hear a humming sound from the outdoor unit while the fan doesn’t spin. Capacitors are one of the most common AC repairs and one of the cheapest parts, but they must be replaced by someone trained to discharge them safely.
6. Frozen evaporator coil
Look at the large copper line going into the outdoor unit and at the indoor unit near the furnace. Frost or ice means the indoor coil is frozen. Turn the thermostat to OFF and the fan to ON for a few hours to thaw it, then replace the filter and make sure every supply and return vent is open. If it freezes again, low refrigerant or a weak blower is likely. Details: AC Unit Freezing Up: Why It Happens and What to Do.
7. Low refrigerant (a leak)
Air conditioners don’t “use up” refrigerant. If the charge is low, there is a leak. Signs include ice on the lines, a hissing sound, higher bills and long run times with weak cooling. A technician needs to find and repair the leak, then recharge the system. Topping it off without fixing the leak only buys a few weeks. Learn what that costs: AC Refrigerant Recharge Cost.
8. A clogged condensate drain
Many systems have a float switch that shuts the AC off when the drain pan fills with water. In some setups the indoor fan keeps running while the compressor stays off, so you feel warm air. Clear the drain line and the switch resets. See How to Clean an AC Drain Line.
9. Leaky or disconnected ductwork
If only some rooms get warm air, a duct may have come loose in the attic or crawl space. Attic air in summer can easily exceed 130°F, and pulling it into a return duct makes the whole system blow warm. Look for flattened, torn or disconnected ducts if you can access them safely.
10. A failing compressor
If the outdoor fan spins but the large black compressor doesn’t run, or the breaker trips seconds after starting, the compressor may be failing. This is the most expensive repair on an air conditioner. On older systems, it usually triggers the repair-or-replace conversation: Repair or Replace Your AC? A Simple Decision Rule.
11. The system is undersized or the heat wave is extreme
Most systems are designed to keep the house about 20 degrees cooler than outside. On a 105°F day, an older or undersized system may run nonstop and still deliver air that feels only slightly cool. Close blinds on the sunny side, avoid using the oven, and check whether your system is correctly sized: What Size AC Do I Need?
Quick diagnosis table
What you notice
Most likely cause
DIY or pro?
Air warm only when fan is set to ON
Thermostat fan setting
DIY
Outdoor unit silent, indoor fan running
Breaker, disconnect, capacitor, contactor
Check breaker yourself, then pro
Outdoor unit humming, fan not spinning
Bad capacitor or fan motor
Pro
Ice on copper lines
Dirty filter, low airflow or low refrigerant
Filter is DIY, refrigerant is pro
Water around indoor unit and AC stopped
Clogged condensate drain
DIY
Some rooms warm, others fine
Duct leak or closed dampers
DIY inspection, pro repair
When to call a technician
Call a licensed HVAC technician if the breaker trips more than once, you hear buzzing or clicking without the fan starting, you see ice that returns after a fresh filter, or you smell burning. Ask for a written diagnosis and price before work starts. If your system is over 12 years old, ask for both a repair quote and a replacement quote so you can compare. Our checklist: How to Compare HVAC Quotes.
Frequently asked questions
How long should I wait for cold air after turning the AC on?
You should feel cool air within a few minutes. Many systems have a built-in delay of up to 5 minutes before the compressor restarts, which protects it. If the air is still warm after 15 to 20 minutes, start troubleshooting.
Can low refrigerant fix itself?
No. Low refrigerant always means a leak. It needs a repair by a certified technician.
Is it safe to keep running an AC that blows warm air?
Not if there is ice on the coil, a burning smell or a humming outdoor unit. Running it can damage the compressor. Turn cooling off and diagnose first.
Why is my car-style “freon” recharge kit not recommended?
Home systems require EPA-certified technicians to handle refrigerant. DIY cans for home systems often contain sealants or the wrong refrigerant and can contaminate the system.
Replacing a central air conditioner in 2026 typically costs about 5,000 to 12,000 USD installed for most homes, including the outdoor unit and a matching indoor coil. Smaller, basic systems can come in lower; high-efficiency variable-speed systems, difficult installations and full system replacements (AC plus furnace or air handler) can cost much more. Price depends mostly on size, efficiency, brand, ductwork condition and local labor rates.
Quick answers
Typical range: roughly 5,000–12,000 USD for AC + coil.
AC + furnace or air handler together: often 9,000–20,000+ USD.
New refrigerant systems (R-454B, R-32) require a matching indoor coil.
Get at least three written quotes with model numbers.
Check utility rebates and manufacturer promotions.
Typical price ranges by size
These are typical installed ranges for replacing an outdoor unit and indoor coil in an existing duct system. Your local prices may be higher or lower.
System size
Basic efficiency (14.3–15 SEER2)
Mid efficiency (16–17 SEER2)
High efficiency (18+ SEER2, variable speed)
2 tons
4,500–7,000 USD
6,000–8,500 USD
8,500–12,000 USD
3 tons
5,500–8,000 USD
7,000–10,000 USD
9,500–14,000 USD
4 tons
6,500–9,500 USD
8,000–11,500 USD
11,000–16,000 USD
5 tons
7,000–10,500 USD
9,000–12,500 USD
12,000–18,000 USD
What drives the price
Size (tons): larger systems cost more. Make sure the size is based on a load calculation: What Size AC Do I Need?
Efficiency and compressor type: variable-speed equipment costs much more upfront.
Brand and warranty: premium brands and longer labor warranties cost more.
Matching indoor equipment: with new refrigerants, the indoor coil must match. If your furnace or air handler is old, replacing it at the same time may be recommended.
Ductwork: leaky, undersized or damaged ducts may need repair.
Electrical work: new disconnects, breakers or panel upgrades.
Access: attic installations, rooftop units or tight spaces add labor.
Permits and local codes: most areas require a mechanical permit.
Season: peak-summer emergency replacements leave less room for negotiation.
What a complete quote should include
Brand, model numbers and SEER2/EER2 ratings for outdoor unit and indoor coil (check the AHRI-matched rating)
Load calculation method
Removal and disposal of old equipment, including refrigerant recovery
New line set or flushing of existing lines
Pad, disconnect, whip and electrical work
Thermostat (if included)
Permit and inspection
Labor warranty length, and who registers the manufacturer warranty
Use our checklist: How to Compare HVAC Quotes.
Ways to lower the cost
Get three or more quotes. Prices for the same equipment can vary widely.
Replace in spring or fall, when contractors are less busy.
Check utility rebates for higher-efficiency equipment.
Ask about manufacturer rebates and financing promotions; read the APR terms carefully. See HVAC financing tips.
Don’t overbuy efficiency in a mild climate. See SEER2 Ratings Explained.
Consider a heat pump if your furnace is also near the end: Heat Pump Installation Cost.
Repair instead?
If your AC is under 10 years old and needs a moderate repair, repair is usually the better value. Guide: Repair or Replace Your AC?
Frequently asked questions
How long does AC installation take?
Most straightforward replacements take one day. Complex jobs with duct or electrical work can take two or more.
Is it cheaper to replace only the outdoor unit?
With new refrigerant systems, you generally can’t pair a new outdoor unit with an old R-410A coil. A matched system is required for proper performance and warranty.
Is the federal tax credit available for central AC in 2026?
The federal 25C credit ended for equipment placed in service after December 31, 2025. Check state and utility programs. Details.
Replacing a gas furnace typically costs about 3,500 to 8,000 USD installed for most homes, while an electric furnace is often 2,500 to 6,000 USD. High-efficiency condensing furnaces (95%+ AFUE) with two-stage or modulating burners cost more, and installations that need new venting, gas lines or ductwork add to the total.
Quick answers
Gas furnace (80% AFUE): often 3,000–5,500 USD installed.
Gas furnace (95%+ AFUE, condensing): often 4,500–8,500 USD.
Electric furnace: often 2,500–6,000 USD.
Switching from 80% to 95%+ often requires new PVC venting and a condensate drain.
Get quotes with model numbers and AFUE ratings.
Typical price ranges
Furnace type
Typical installed range
Electric furnace
2,500–6,000 USD
Gas, 80% AFUE, single-stage
3,000–5,500 USD
Gas, 95–97% AFUE, single-stage
4,500–7,000 USD
Gas, 96%+ AFUE, two-stage variable-speed blower
5,500–8,500 USD
Gas, modulating, premium
7,000–11,000+ USD
Oil furnace
5,500–10,000 USD
These are planning ranges for replacements in existing ductwork. Local prices vary.
What adds to the cost
Venting changes: going from an 80% furnace (metal flue) to a condensing furnace requires PVC venting and may leave a water heater needing a liner for the old chimney.
Condensate drain or pump for high-efficiency furnaces.
Gas line upgrades if the new furnace needs more capacity.
Ductwork modifications to fit the new furnace or fix airflow problems.
AC coil compatibility: if the existing AC coil doesn’t fit or match, it may need replacement.
Attic or crawl space installation.
Permits and inspections.
Is a high-efficiency furnace worth it?
It depends on your climate and gas price. In a cold climate with high heating bills, the savings from 96% vs 80% AFUE can pay back the higher price within several years. In mild climates, the payback may be very long.
Annual gas heating bill (80% furnace)
Approximate yearly savings at 96% AFUE
600 USD
~100 USD
1,200 USD
~200 USD
2,000 USD
~335 USD
Savings are estimated as the reduction in fuel used: 1 − (80 ÷ 96) ≈ 17%.
Gas or something else?
If your AC is also old, compare a heat pump or dual-fuel system before replacing like-for-like. See Heat Pump vs Furnace and Gas vs Electric Furnace.
How to avoid overpaying
Get a load calculation, not a size based on the old furnace. (What Size Furnace Do I Need?)
Replace before it fails, ideally in spring or early fall.
Check utility rebates for high-efficiency equipment.
Quote checklist: How to Compare HVAC Quotes.
Frequently asked questions
How long does furnace installation take?
Usually 4 to 10 hours for a straightforward replacement.
Can I replace the furnace without replacing the AC?
Yes, if the AC coil is compatible with the new furnace and in good condition. If the AC is old, replacing both together can save labor.
A heat pump can blow air that feels cool for three normal reasons: its supply air is naturally less hot than a furnace’s, it’s in a defrost cycle, or it’s running in very cold weather. It’s a problem if the air stays cool for long periods, the house can’t reach the set temperature, or ice builds up on the outdoor unit. Common real causes include thermostat settings, a dirty filter, a stuck reversing valve, low refrigerant or failed backup heat.
Quick answers
Heat pump air at the vents is often 90–110°F, which can feel cool against your hand (your skin is about 93°F).
Defrost cycles can blow cool air for a few minutes. Normal.
Check the thermostat is in HEAT (not COOL or FAN ON) and configured for a heat pump.
Replace the filter and clear snow or debris around the outdoor unit.
Cold air all the time with the outdoor unit running = call a technician.
Is it really cold, or just “not hot”?
Hold a thermometer at a supply vent after the system runs 10 minutes. If the air is 85°F or more and the house is slowly warming, the system is working. If air is close to room temperature or colder, something’s wrong.
1. Thermostat settings
Mode should be HEAT.
Fan should be AUTO. With ON, the blower runs between cycles and air feels cool.
System type: if a new thermostat is set up for a gas furnace instead of a heat pump, the reversing valve can be energized wrong, so the system cools instead of heats. Check the installer settings or the “O/B” wire setup. See Thermostat Wiring Colors Explained.
2. Defrost mode
In cold, damp weather, frost builds on the outdoor coil. The heat pump temporarily switches to cooling mode to melt it, typically for 5 to 15 minutes. You might see steam outside. Many systems turn on backup heat during defrost so indoor air doesn’t feel cold. Details: Heat Pump Defrost Mode.
3. Very cold outdoor temperatures
As it gets colder, a standard heat pump’s output drops. If the backup heat isn’t working, air temperature falls and the house loses ground. Check whether “AUX” or “AUX HEAT” appears on the thermostat. If it shows but the air stays cool, the backup heat strips or their breaker may have failed.
4. Dirty filter or blocked airflow
A clogged filter reduces airflow and heating capacity. Replace it and open all vents.
5. Outdoor unit blocked by snow, ice or debris
The outdoor coil needs airflow. Clear snow, leaves and ice around it, carefully, without chipping at the coil. If the unit is encased in ice that doesn’t melt, see Heat Pump Frozen in Winter.
6. Stuck reversing valve
The reversing valve switches the system between heating and cooling. If it sticks in cooling position, the heat pump blows cold air in heat mode, and often the outdoor unit blows warm air. This needs a technician to diagnose and repair.
7. Low refrigerant
A leak reduces heating capacity. Signs include longer run times, ice on parts of the outdoor coil that doesn’t clear, and higher bills. Leaks need a professional repair.
8. Failing compressor or outdoor fan
If the outdoor unit hums but doesn’t run, or the fan doesn’t spin, the problem may be a capacitor, contactor, fan motor or compressor. Call a technician.
Why does my heat pump blow cold air at the start of a cycle?
Until the coil warms up, the first air can feel cool. It should warm within a minute or two.
Should I switch to emergency heat if it blows cold air?
Only if the heat pump itself has failed and you need heat until a technician arrives. Emergency heat costs much more to run.
Can a heat pump heat in 20°F weather?
Yes. Most can, and cold-climate models can heat effectively at much lower temperatures.
When a gas furnace won’t ignite, the most common causes are a dirty flame sensor, a failed hot surface igniter, a closed gas valve, a clogged filter or condensate drain, or a safety switch that has tripped. Modern furnaces follow a fixed startup sequence, so noticing where it stops tells you where to look. Before anything else: if you smell gas, leave the house and call your gas utility or 911 from outside.
Quick answers
Smell of gas: don’t touch switches, leave the home, call the gas company from outside.
Check the thermostat is set to HEAT and above room temperature.
Replace a dirty filter and make sure the furnace switch is ON.
Flame lights then goes out after a few seconds: usually a dirty flame sensor.
No orange glow from the igniter: likely a failed igniter.
How a gas furnace starts
Most furnaces built in the last 25 years follow this sequence:
The thermostat calls for heat.
The draft inducer motor starts to vent the combustion chamber.
The pressure switch confirms the venting is working.
The hot surface igniter glows bright orange (or a spark igniter clicks).
The gas valve opens and burners light.
The flame sensor confirms a flame within a few seconds.
After a short delay, the blower starts to send warm air through the house.
If any step fails, the control board stops and tries again. After several failed attempts, many furnaces go into a lockout for about an hour.
Start with these quick checks
Thermostat: set to HEAT and at least 3 degrees above room temperature. Replace the batteries if the screen is dim or blank.
Furnace power switch: looks like a light switch on or near the unit. It should be ON.
Breaker: check the furnace breaker in your panel.
Furnace door: the front panel must be fully closed to press the safety switch.
Air filter: a clogged filter can make the furnace overheat and shut down. Replace it.
Gas supply: the gas valve handle on the pipe leading to the furnace should be parallel to the pipe. Make sure other gas appliances work.
Condensate drain (high-efficiency furnaces): if the drain or trap is clogged, a pressure switch may stop ignition.
Where the sequence stops, and why
What you observe
Likely cause
Nothing happens at all
No power, thermostat, door switch, blown control fuse
Inducer runs, no igniter glow
Pressure switch issue, blocked vent or drain, failed igniter
Igniter glows, no flame
Gas valve closed or faulty, no gas supply
Flame lights, then shuts off in 3–10 seconds
Dirty flame sensor, poor ground
Burners run, blower never starts
Blower motor, capacitor or limit switch issue
Repeats several times then stops
Lockout after failed attempts
Fix 1: Clean the flame sensor
The flame sensor is a thin metal rod in front of the burners. Over time it gets a coating that weakens its signal, so the control board thinks there’s no flame. Cleaning it is one of the most common DIY furnace fixes. Step-by-step: Furnace Flame Sensor: How to Clean It Safely.
Fix 2: Check the igniter
Watch through the sight glass when the furnace starts. A working hot surface igniter glows bright orange within a few seconds. If it doesn’t glow, it may be cracked or burned out. Igniters are fragile ceramic parts. Replacement is a moderate DIY job for experienced homeowners but is often best left to a technician, who will also confirm the cause.
Fix 3: Clear the vent and condensate drain
High-efficiency furnaces vent through PVC pipes, often out the side of the house. Snow, ice, leaves or nests can block them. Check outside that both pipes are clear. Inside, look for water in the condensate trap and tubing. A blocked drain is common after a long summer of AC use.
Fix 4: Reset after a lockout
Turn the furnace switch off for 30 seconds and back on, or turn the thermostat off and on. This clears a lockout. If the furnace fails again, the underlying problem remains. Don’t reset repeatedly.
Read the diagnostic light
Most control boards have an LED that blinks a code. The code chart is usually printed on the inside of the furnace door. Read it before calling a technician. Guide: Furnace Blinking Light: How to Read Your Furnace’s Code.
When to call a professional
Call a licensed technician if:
You smell gas or see scorch marks
The igniter or gas valve needs replacement and you’re not experienced with gas appliances
The pressure switch keeps failing (this can indicate venting problems)
The furnace is more than 15 years old and has repeated failures
Frequently asked questions
Why does my furnace click but not turn on?
Clicking usually comes from relays on the control board or a spark igniter. If the burners don’t light, check the gas supply, igniter and pressure switch.
How long should a furnace take to ignite?
Usually 30 to 90 seconds from the thermostat call, including the inducer pre-purge.
Can I relight my furnace’s pilot light?
Only older furnaces have standing pilot lights. Follow the instructions on the furnace label. Most modern furnaces have no pilot to relight.
Each thermostat terminal controls one function: R supplies 24-volt power, C completes the circuit, W calls for heat, Y calls for cooling, G runs the fan, and O/B controls a heat pump’s reversing valve. Wire colors usually match the terminal letter (red for R, white for W, yellow for Y, green for G), but installers don’t always follow the convention. Always go by which terminal the wire is connected to at the furnace or air handler, not just by color.
Quick answers
Turn off power at the breaker before touching thermostat wires.
Photograph the existing wiring before disconnecting anything.
Thermostat wires are low voltage (24V), but thick wires at 120V or 240V mean a line-voltage thermostat: don’t use a standard thermostat with those.
Heat pumps use O or B for the reversing valve; set this correctly in the thermostat menu.
Terminal guide
Terminal
Typical wire color
Function
R / Rh / Rc
Red
24V power. Rh for heating, Rc for cooling; often joined with a jumper on single-transformer systems
C
Blue or black (varies)
Common wire; completes the 24V circuit to continuously power smart thermostats
W / W1
White
Heat call (furnace or first stage of heat)
W2 / AUX
Brown or other
Second stage heat or auxiliary heat
E
Varies
Emergency heat (some heat pump systems)
Y / Y1
Yellow
Cooling call (compressor), and heating too on heat pumps
Y2
Light blue or other
Second stage compressor
G
Green
Fan
O
Orange
Reversing valve energized in cooling (most brands)
B
Dark blue or brown
Reversing valve energized in heating (some brands)
Common wiring setups
Gas furnace with central AC (conventional)
R (red), W (white), Y (yellow), G (green), and ideally C.
Thermostat set to “conventional” or “furnace” system type.
Heat pump with electric backup
R, Y (compressor), G (fan), O or B (reversing valve), AUX/W2 (backup heat), C.
Thermostat set to “heat pump” system type, with the O/B setting matching your equipment.
Heat only (furnace, no AC)
R and W, often with G and C.
Rh and Rc explained
Some systems have separate transformers for heating and cooling (common with a boiler plus a separate AC). In that case, the thermostat keeps Rh and Rc separate. Most forced-air systems have one transformer, so Rh and Rc are connected with a jumper.
O vs B: getting it right
If a heat pump blows cold air in heat mode after installing a new thermostat, the O/B setting is probably reversed. Most brands energize the reversing valve in cooling (O). A few brands use B (energized in heating). Check your equipment’s manual or the existing thermostat’s settings.
How to wire a thermostat safely
Turn off the breaker for the furnace or air handler.
Remove the old thermostat cover and take a clear photo of the terminals.
Label each wire with its terminal letter (most new thermostats include stickers).
Disconnect wires and wrap the bundle around a pencil so it doesn’t fall into the wall.
Mount the new base, connect wires to matching terminals.
Attach the thermostat, restore power and configure the system type.
Full walkthrough: How to Replace a Thermostat Yourself.
What if the colors don’t match?
Open the furnace or air handler (power off) and look at the control board. The wire color connected to the board’s “W” terminal is your heat wire, and so on. That’s the reliable way to identify wires.
Frequently asked questions
What if I don’t have a C-wire?
Many smart thermostats need one. Options include an unused wire in the bundle, an adapter, or running a new cable. See Do I Need a C-Wire for a Smart Thermostat?
Can I damage my system with wrong wiring?
Yes. Shorting R to C can blow the control board fuse or damage the transformer. Keep power off while wiring.
Can I use a regular thermostat with baseboard heaters?
No. Electric baseboards usually use line-voltage thermostats rated for 120V or 240V.
A standard tank water heater is the cheapest to buy, a tankless model lasts longer and never runs out of hot water at its rated flow, and a heat pump water heater usually has the lowest operating cost if you currently heat water with electricity. For most households replacing a working gas tank, another gas tank or a tankless unit makes sense. For households with electric water heating, a heat pump water heater is often the best long-term value.
Quick answers
Tank: lowest upfront cost, about 8–12 years of life, limited hot water supply.
Gas tankless: endless hot water at its flow rate, often 20 years of life, higher install cost.
Heat pump water heater: uses roughly a third to half the electricity of a standard electric tank.
Switching from tank to gas tankless may require new gas lines and venting.
Choose based on fuel available, household size and how long you’ll stay in the home.
Side-by-side comparison
Factor
Gas tank
Electric tank
Gas tankless
Heat pump (hybrid electric)
Typical installed price
Low
Lowest
High
Medium to high
Operating cost
Medium
Highest
Lower than gas tank
Lowest of electric options
Typical lifespan
8–12 years
10–15 years
~20 years
10–15 years
Hot water supply
Limited by tank size
Limited by tank size
Unlimited at rated flow
Limited by tank size; slower recovery
Space
Large
Large
Small, wall-mounted
Large, needs surrounding air space
Maintenance
Flush yearly
Flush yearly
Descale yearly in hard water
Clean air filter, flush yearly
Operating cost: how they compare
The DOE’s Uniform Energy Factor (UEF) on the yellow EnergyGuide label lets you compare efficiency directly. Higher UEF means lower operating cost:
Standard gas tank: UEF often around 0.6–0.7
Gas tankless: around 0.8–0.95
Standard electric tank: around 0.9–0.95
Heat pump water heater: often 3.0–4.0 or more
An electric heat pump water heater with a UEF of 3.5 uses roughly a quarter to a third of the electricity of a standard electric tank for the same hot water. The EnergyGuide label also shows estimated yearly operating cost.
10-year cost example
These are illustrative numbers for a family of four. Your costs will differ by prices and usage.
Type
Installed price (example)
Yearly energy cost (example)
10-year total
Gas tank, 50 gal
2,000 USD
350 USD
~5,500 USD
Gas tankless
4,000 USD
270 USD
~6,700 USD
Electric tank, 50 gal
1,600 USD
650 USD
~8,100 USD
Heat pump, 50 gal
3,500 USD
220 USD
~5,700 USD
The tankless unit can come out ahead if it lasts 20 years and avoids a second tank replacement. The heat pump wins against a standard electric tank in most scenarios.
Tankless: pros and cons
Pros: endless hot water at its rated flow rate, small footprint, long life, no standby heat loss.
Cons: higher installation cost, may need a larger gas line and new venting, a short delay before hot water arrives, and limited flow if several showers run at once. Hard water requires regular descaling.
Heat pump water heaters: pros and cons
Pros: very low operating cost, dehumidifies and cools the space it’s in (a plus in garages and basements in warm climates).
Cons: taller and needs space for airflow (often around 700 cubic feet or ventilation), slower recovery in “heat pump only” mode, a fan noise similar to a dehumidifier, and less efficient in cold spaces.
Which should you choose?
Your situation
Good choice
Gas available, tight budget
Gas tank
Gas available, staying 10+ years, high demand
Gas tankless
Electric only
Heat pump water heater
Small home, low usage, limited space
Small tank or point-of-use tankless
Large family, multiple simultaneous showers
Large tank or properly sized tankless
Size it correctly first: What Size Water Heater Do I Need?
Frequently asked questions
Do tankless water heaters really save money?
They save on energy, but higher installation cost lengthens the payback. They make the most sense when they’re expected to last 20 years.
Can a heat pump water heater go in a closet?
Only if the closet has enough air volume or ventilation as specified by the manufacturer.
Is the federal tax credit still available?
The federal 25C credit ended for installations after December 31, 2025. See Heat Pump Tax Credit 2026.
A water heater leaking from the bottom is usually caused by a loose or faulty drain valve, water from the temperature and pressure (T&P) relief valve, condensation, or a corroded tank. The first three can often be fixed for under 50 USD. If the tank itself is leaking, it can’t be repaired and the water heater needs to be replaced. Start by shutting off the power or gas and the cold water supply.
Quick answers
Electric: turn off the breaker. Gas: set the gas control to OFF.
Close the cold water valve at the top of the heater.
Dry the area and look for the source: drain valve, relief valve pipe, fittings or tank.
Water coming from the tank body itself means replacement.
Tank water heaters commonly last about 8 to 12 years.
Step 1: Make it safe
Cut the energy. Electric: switch off the water heater’s breaker. Gas: turn the gas control knob to OFF. Never let an electric heater run with a partly empty tank: the elements can burn out in seconds.
Stop new water. Close the cold water supply valve on the pipe going into the top of the tank.
Protect the floor. Place towels or a pan under the heater. If water is spreading toward outlets or electrical equipment, keep away and call a professional.
Be careful with hot water. Tank water can be hot enough to scald. Let it cool before touching valves.
Step 2: Find where the water comes from
What you see
Likely cause
Fix
Typical cost
Drip from the drain valve near the bottom
Valve not fully closed or worn washer
Tighten it, cap it, or replace the valve
10–40 USD (DIY)
Water at the end of the pipe running down the side
T&P relief valve opening
Check water pressure and temperature; replace valve if it keeps dripping
Important: never cap, plug or remove the T&P relief valve. It protects the tank from dangerous pressure and temperature.
Step 3: Repair or replace?
Repair makes sense when the leak comes from a valve or fitting and the heater is under about 8 years old. Replace it when the tank body is leaking, the heater is 10 or more years old, or you see rusty hot water.
How to check your heater’s age: look at the serial number on the label. Most brands encode the year and month of manufacture in the first characters. Search the brand name with “serial number date code” to decode it.
A real-world example
A homeowner finds a puddle under a 9-year-old 50-gallon gas heater. The drain valve is dry and there’s no water at the end of the relief valve pipe. Looking under the burner access panel, water is dripping from the base of the tank: internal corrosion. The right move is to shut off gas and water, drain the tank to prevent more water damage, and schedule a replacement. Waiting risks a full tank of water on the floor.
How to drain the tank if the body is leaking
Keep the power or gas off and the cold water valve closed.
Connect a garden hose to the drain valve and run it to a floor drain or outside.
Open a hot water faucet in the house to let air in.
Open the drain valve and let the tank empty. Expect sediment at the end.
Detailed guide: How to Flush a Water Heater (Step by Step).
Common mistakes
Turning the power back on before the tank is full again (burns electric elements).
Ignoring a small leak: tank leaks get worse, not better.
Overtightening a plastic drain valve and cracking it.
Plugging the relief valve to stop a drip.
Paying for repairs on a 12-year-old heater instead of planning a replacement.
Frequently asked questions
Is a leaking water heater an emergency?
If water comes from the tank body or near electricity, treat it as urgent. A valve drip should be fixed within days.
Can I still use hot water?
Not if the tank is leaking. Shut it down and plan the replacement.
Does homeowners insurance cover it?
Sudden water damage is often covered, but the water heater itself usually isn’t. Check your policy.
Why is my relief valve dripping?
The tank pressure or temperature is too high, the valve is worn, or your home needs a thermal expansion tank. A plumber can test water pressure.
A dirty flame sensor is one of the most common reasons a gas furnace lights, runs for 3 to 10 seconds, and shuts off. The sensor proves to the control board that a flame is present. When a thin layer of oxide builds up on it, the signal weakens and the furnace shuts the gas off for safety. Cleaning it takes about 15 minutes with a fine abrasive pad and a screwdriver or nut driver.
Quick answers
Symptom: burners light, then go out within seconds, and the furnace retries several times.
Tools: 1/4-inch nut driver or screwdriver, fine abrasive pad or very fine sandpaper, clean paper towel.
Turn off power and gas before starting.
Don’t touch the fragile hot surface igniter next to it.
If cleaning doesn’t help, check the sensor’s ground connection or replace it.
What the flame sensor does
The flame sensor is a thin metal rod, usually bent, with a white ceramic base, mounted so its tip sits in the flame of one burner. The control board sends a tiny electrical current through the flame to the sensor. If the current isn’t detected within a few seconds after the gas valve opens, the board closes the valve. This prevents unburned gas from filling the furnace.
Signs of a dirty flame sensor
Burners light, then shut off after a few seconds
The furnace tries several times, then goes into lockout
The diagnostic LED shows a flame sense or ignition failure code (how to read it)
The problem gets worse over weeks
Safety first
Set the thermostat to OFF.
Turn off the furnace power switch (and the breaker if you’re unsure which switch is the furnace).
Turn the gas valve on the furnace supply pipe to OFF (handle perpendicular to the pipe).
Wait for the furnace to cool if it was just running. Burner areas get very hot.
If you smell gas at any point, stop, leave the house and call your gas utility from outside.
Step-by-step cleaning
Remove the furnace front panel(s). Usually the upper panel lifts off.
Find the burners and look for the flame sensor: a thin rod with a single wire attached, held by one screw. Don’t confuse it with the igniter, which is a flat or round gray/black ceramic element with two wires. The igniter is extremely fragile.
Take a photo so you remember the position.
Remove the screw holding the sensor bracket (often 1/4-inch hex).
Pull the sensor out gently. You can leave the wire connected or disconnect it if it slides off easily.
Clean the metal rod by rubbing lightly with a fine abrasive pad (like a non-scratch scouring pad) or very fine sandpaper until it’s bright. Don’t use coarse sandpaper or a file, which can scratch the surface and make it dirty faster.
Wipe it with a clean paper towel. Don’t touch the cleaned rod with your fingers.
Reinstall it in the exact same position, tighten the screw firmly (the screw also provides the ground), and reconnect the wire.
Replace the panel, turn the gas back on, restore power and set the thermostat to HEAT.
Watch a full cycle through the sight glass. Burners should stay lit.
If it still shuts off
Possible cause
What to check
Sensor cracked or worn
Look for cracks in the ceramic base; replace the sensor (inexpensive part)
Poor ground
Tighten the sensor screw and check the furnace ground wire
Sensor out of the flame
Make sure the tip sits in the flame path
Wrong polarity on power supply
Some boards need correct hot/neutral wiring; a technician can test
Weak flame
Low gas pressure or dirty burners; requires a technician
Control board
Less common; a technician can measure the flame signal in microamps
How often should you clean it?
During a yearly tune-up, a technician usually checks and cleans the flame sensor. If yours needs cleaning every few weeks, something else is causing contamination, such as dirty combustion air, a lot of dust near the furnace, or chemical fumes from nearby storage.
Frequently asked questions
Can I use steel wool?
It’s better to avoid it. Steel wool can leave fibers behind. Use a fine abrasive pad or very fine sandpaper.
How much does a new flame sensor cost?
The part itself is usually inexpensive (often 10 to 40 USD). A service call to replace it costs more, typically including the diagnostic fee.
Is it safe to bypass the flame sensor?
No. Never bypass a safety device. The sensor prevents gas from building up in the furnace.
If your air conditioner or heat pump uses R-410A, you don’t have to replace it. It can keep running and be repaired for years. What changed is that new residential systems manufactured since January 1, 2025 must use lower-impact refrigerants, mainly R-454B and R-32. As production of new R-410A is reduced, the cost of refrigerant for repairs is expected to keep rising, which matters most if your system develops a leak.
Quick answers
Existing R-410A systems are legal to use and service.
New systems use R-454B or R-32, which cannot be added to an R-410A system.
A small repair on a newer R-410A system is usually worth it.
A major leak on a 12+ year-old system is often the moment to replace.
You can’t mix a new outdoor unit with an old R-410A indoor coil.
Why R-410A is being phased down
Under the federal AIM Act, the EPA is reducing the production and import of hydrofluorocarbons (HFCs), refrigerants with a high global warming potential (GWP). R-410A has a GWP of about 2,088. The replacements have much lower values: R-454B is around 466 and R-32 about 675.
The rules work in two ways:
New equipment: since 2025, new residential air conditioners and heat pumps must be built for lower-GWP refrigerants. A limited window allowed installers to finish installing R-410A split-system components that were already manufactured.
Refrigerant supply: the total allowed production of HFCs keeps stepping down. Industry reports describe 2026 production allowances at about 60% of the original baseline. Recovered and recycled R-410A will remain available for servicing existing systems.
What it means for your current system
If your system is working well
Keep using it. Schedule regular maintenance, keep the filter clean and the outdoor coil clear. A system that never leaks never needs new refrigerant. See the HVAC Maintenance Checklist: Spring and Fall.
If your system needs a non-refrigerant repair
Capacitors, contactors, fan motors, control boards and thermostats are unaffected by the phase-down. These repairs make sense on most systems under 12 to 15 years old.
If your system has a refrigerant leak
This is where the phase-down matters. A leak repair now includes:
The leak search and repair itself
Recovering the remaining refrigerant
Recharging with R-410A at current prices, which have been climbing
On a newer system, a leak at a fitting or valve is usually worth fixing. On an older system with a leaking evaporator or condenser coil, the repair can approach a large share of the cost of a new system.
If the compressor fails
A compressor replacement on an older R-410A system is rarely a good investment. You’d be putting an expensive new part into an aging system that still uses a refrigerant with rising costs. Get replacement quotes.
Can you put R-454B or R-32 into an R-410A system?
No. The new refrigerants are classified A2L (mildly flammable) and operate at different pressures. Equipment designed for them includes refrigerant leak sensors and other safety features. Mixing refrigerants or “converting” a system is not a safe or legal shortcut.
Can you replace only the outdoor unit?
Not with a new-refrigerant model. A new R-454B or R-32 condenser needs a matching indoor coil (and often a compatible furnace or air handler). Replacing both sides together is the standard approach now, which is one reason new installation quotes are higher than a few years ago.
Some sales pitches suggest R-410A systems must be replaced immediately. That’s not true. Replacement should be based on your system’s age, condition, repair history and energy costs, not on the phase-down alone.
Frequently asked questions
Will R-410A be banned for repairs?
Current rules phase down production, not the use of existing systems. Recycled and reclaimed refrigerant will keep supplying repairs.
How do I know what refrigerant my system uses?
Look at the data plate on the outdoor unit. It lists the refrigerant type and factory charge.
Are new refrigerant systems safe in my home?
Yes. A2L refrigerants have low flammability and new equipment is designed with sensors and safety controls for them. Installation must follow updated codes.
