Furnace and AC Troubleshooter
What's happening?
Gas and Carbon Monoxide
- If you smell gas: get out, warn others, don't touch anything that could spark, and call 911 from a safe distance, then MG&E (608-252-7000, or 1-800-245-1125 long distance).(MG&E) Alliant Energy customers call 1-800-255-4268; Alliant checks a suspected leak for free.(Alliant Energy)
- If the CO alarm sounds: go outside to fresh air, call 911, and stay out until responders say it's safe.(CPSC) If no one has symptoms, MG&E will check, but says the visit will probably cost a fee.(MG&E)
- Wisconsin's CO alarm law requires a working alarm in the basement and on every floor level of a one- or two-family home with a fuel-burning appliance, a fireplace or an attached garage. Hardwired alarms need battery backup.(Wis. Stat. 101.647) Homes permitted since February 1, 2011 need hardwired, interconnected alarms within 21 feet of each bedroom door.(SPS 321.097)
- CPSC recommends a yearly professional inspection of the furnace, water heater, flues and vents.(CPSC) Check CO alarm batteries when the clocks change in spring and fall.(CDC)
- Flame sensors, igniters, gas valves and the heat exchanger are jobs for a trained technician.(Carrier) Never try to light the burners with a match; modern furnaces light themselves.(Carrier)
- Unvented gas or kerosene space heaters are banned in Wisconsin homes.(SPS 323)
Winter Vents
Madison's normal coldest night of the year is −17°F. A normal year has 7,138 heating degree days and 627 cooling degree days, so heating is by far the bigger job.(National Weather Service)
- High-efficiency furnaces vent through plastic pipes. After heavy snow, ice or freezing fog, check the pipe ends outside and clear them.(Lennox) A blocked pipe shuts the furnace down and can let carbon monoxide build up.(MG&E)
- Screens over the pipe ends cause freeze-ups. The condensate drain line should run through heated space so it doesn't freeze.(Lennox)
- Older furnaces with metal vents: look over the vent pipe each heating season for sags, holes, rust or loose joints. If it's damaged, don't run the furnace until it's repaired.(Carrier)
Filters and Maintenance
- Filter: check it monthly and change it when it's dirty, at least every 3 months. A dirty filter slows airflow and wastes energy.(ENERGY STAR)
- Tune-ups: have a contractor check heating in the fall and cooling in the spring.(ENERGY STAR)
- Keep supply and return grilles open, and don't store paint, cleaners, laundry products or softener salt near the furnace; their fumes can corrode it.(Carrier)
- Outdoor unit: keep at least 2 feet clear on every side and 4 feet above.(Trane)
- A plugged condensate drain can cause water damage and humidity problems.(ENERGY STAR)
Repair or Replace
- ENERGY STAR suggests considering replacement for a furnace or boiler older than 15 years or a heat pump or AC older than 10. Other signs: frequent repairs, rising bills, rooms too hot or cold, and noise.(ENERGY STAR)
- Sizing: ask for a Manual J load calculation. Bad installation can cut performance by as much as 30%.(ENERGY STAR) Wisconsin's code requires systems sized to hold indoor temperature on the coldest design day.(SPS 323)
- Ask for the AHRI certificate showing the indoor and outdoor units are a matched system, and for duct leakage of no more than 20%.(ENERGY STAR)
- Cold-climate heat pumps: ENERGY STAR's cold-climate label requires at least 70% of rated heating capacity at 5°F.(ENERGY STAR) Wisconsin's code requires backup heat sized for the coldest design day.(SPS 323)
Refrigerants and Efficiency Rules
- R-22 (older AC): no new R-22 has been made or imported since 2020, but you can keep using and repairing the system with reclaimed R-22. Don't let anyone add "R-22a"; EPA says it's flammable.(EPA)
- R-410A: new systems are moving to lower-impact refrigerants. Under EPA's May 2026 rule, existing systems can be repaired for their useful life, including replacing parts. Adding cooling capacity counts as a new installation.(EPA)
- Federal minimums in Wisconsin: 80% AFUE for indoor gas furnaces; 13.4 SEER2 for split AC; 14.3 SEER2 and 7.5 HSPF2 for split heat pumps.(10 CFR 430.32)
- A 95% AFUE furnace minimum is in the regulations for furnaces made from December 18, 2028, but it's under review: the Supreme Court sent the court case back in June 2026,(Supreme Court) and DOE has taken comment on an industry request to delay it to at least 2030.(Federal Register)
Rebates
- Focus on Energy takes an instant discount off the contractor's invoice: $100 for a gas furnace of 95% AFUE or higher ($400 income-qualified), and $400 to $900 for an air-source heat pump, by efficiency and income. There's no central AC rebate in 2026.(Focus on Energy)
- Households under 150% of area median income can get up to $8,000 toward a heat pump from federal HEAR, plus help with an electrical panel or wiring.(Focus on Energy)
- The federal tax credit for furnaces, AC and heat pumps (25C) doesn't cover anything installed in 2026.(IRS)
Every amount, by income, is in the energy rebates guide.
Permits and Licenses
- Madison requires a permit to install a furnace or central air conditioner.(City of Madison) HVAC contractors can apply online for jobs that don't need plan review.(City of Madison)
- Fees for replacement heating equipment: $25 up to 100,000 BTU, $50 up to 165,000, and $75 above. A new or replaced AC unit or ductless split is $25.(City of Madison) Ask for the final inspection when the work is done.(City of Madison)
- State registration: anyone in the business of installing or servicing heating and cooling equipment must register with DSPS.(Wis. Stat. 101.178) Look up a company's HVAC Contractor credential, not the Dwelling Contractor one, which doesn't cover HVAC-only firms.(DSPS)
Town-by-town rules for other projects are in the remodel permit guide.
Help Paying for Heat
- WHEAP opened October 1, 2026 for the 2026–27 heating season. The income limit is 60% of state median income: $39,864 for one person, $64,395 for three, $76,661 for four.(State of Wisconsin)
- Crisis help runs year-round, and eligible homeowners may get emergency furnace repair or replacement. With no heat, contact your local agency right away; agencies run a 24-hour crisis line. Apply at energybenefit.wi.gov or call 1-866-432-8947.(Wisconsin DOA)
- MG&E sends Dane County customers to Energy Services, Inc.: 1-800-506-5596.(MG&E)
- Winter rule: from November 1 through April 15, a utility can't disconnect the service that runs your main heat. You can ask for a deferred payment agreement; PSC Consumer Affairs is 1-800-225-7729.(PSC of Wisconsin)
- Scammers call pretending to be utilities and threatening shutoff. Hang up and call the number on your bill. A demand for payment by gift card, crypto, wire or barcode is a scam.(DATCP)
Renters
- Madison takes heating complaints when a rental is below 67°F, and landlords can't pick dates to turn the heat on or off.(City of Madison)
- Contact the landlord first. If it isn't fixed in a reasonable time, report it online or call Building Inspection at 608-266-4551.(City of Madison)
- The city's guide to repair time depends on the weather: about a week when lows are in the 60s, a day in the 40s, and immediately below freezing.(City of Madison)
Hiring a Heating and Cooling Contractor in Wisconsin
Furnace and AC replacement falls under Wisconsin's home improvement rule (ATCP 110):(ATCP 110)
- If you pay anything before the work is done, you need a written contract listing the equipment by make, model and size, the total price, dates and warranties. The contractor must tell you about required permits before you sign.
- It's illegal to falsely tell you your equipment is dangerous, defective or due for replacement. Before replacing a furnace over a "cracked heat exchanger" or similar warning, a second opinion is reasonable.
- Get more than one estimate, from contractors who see the job in person. Contracts over $25 signed at your home can be canceled within three business days.(DATCP)
- Check the company's DSPS HVAC registration and its complaint history with DATCP's Consumer Protection Hotline, (800) 422-7128.(DATCP)
Questions
What should I check before calling for furnace repair?
Thermostat on HEAT and set above room temperature, the furnace switch and breaker on, the blower door fully closed, the gas valve handle parallel to the pipe, and a clean filter. On a high-efficiency furnace, check that snow isn't blocking the plastic vent pipes outside.
What do I do if I smell gas?
Leave right away and take everyone with you. Don't use switches or phones inside. From a safe distance, call 911 and your gas utility: MG&E at 608-252-7000 or Alliant Energy at 1-800-255-4268.
Does Wisconsin require carbon monoxide alarms?
Yes. State law requires a working CO alarm in the basement and on every floor level of a one- or two-family home that has a fuel-burning appliance, a fireplace or an attached garage. Homes permitted since February 1, 2011 need hardwired, interconnected alarms with battery backup.
Should I repair or replace my furnace or AC?
ENERGY STAR suggests considering replacement for a furnace or boiler more than 15 years old or a heat pump or AC more than 10 years old, especially with frequent repairs, rising bills or rooms that won't stay comfortable. Ask for a Manual J load calculation so the new system is sized to your house.
Can I still repair an older air conditioner?
Yes. EPA says you can keep using and repairing an R-22 system, and existing R-410A systems can be repaired too, including replacing parts. Don't let anyone add R-22a, which EPA says is flammable and not an approved substitute.
Does Madison require a permit to replace a furnace or AC?
Yes. Madison requires a permit to install a furnace or central air conditioner. HVAC contractors can apply online. Fees for replacement heating equipment start at $25.
Is there a rebate for a new furnace or heat pump?
Focus on Energy takes $100 off a 95%-efficient gas furnace ($400 income-qualified) and $400 to $900 off an air-source heat pump, depending on efficiency and income. Households under 150% of area median income may also get up to $8,000 toward a heat pump from the federal HEAR program. The federal tax credit ended for 2026 installs.