Before the first very hot or cold week, check your heating and cooling

Heating and cooling get little attention while they work. The attention comes on the first very hot day or the first hard frost, which is also when repairs are hardest to book. Many people who shared advice on this suggest running the system once before that day, so a fault turns up while there is still time to fix it. The US government’s ENERGY STAR program gives the reason: contractors get busy once summer and winter come.

Before the first very hot or very cold week, run your heating or cooling once, check the filter, and book the yearly professional check while contractors are not yet busy.

This page is about central heating and cooling in a home in the US or UK: a furnace or boiler, a central air conditioner or heat pump, ducts and a thermostat. The gas, carbon monoxide and electrical parts come first below, because those are the parts that can hurt you.

Who this page is not for

• If your heating or cooling has already failed in extreme weather, a check-up is too slow. The page The power or heat is off. How do I stay warm? and the tip Keep the heat out before it arrives are for that. If anyone is confused or has collapsed, call 911 or 999.
• If you live where cooling runs most of the year, “test it before the first hot day” does not fit you. Some people in hot places say their cooling runs most of the year, so a first-warm-day test has nothing to catch. The filter and the drain, below, still apply to you.
• If you rent in a building with one shared system, the filter and the yearly service may be your landlord’s. See “If you rent”.
• Window units, portable units, a car’s air conditioning and commercial coolers are different machines. This page does not cover them.
• This page covers the US and the UK only.

Gas, carbon monoxide and electricity first

If you smell gas

In the US, the Pipeline and Hazardous Materials Safety Administration (PHMSA) says to turn off gas appliances, leave the area on foot straight away, not try to find the source, and call 911 from a safe location. It also says not to cause a flame or a spark. Its page was last updated in May 2017 and is written about pipelines, so treat it as a general guide, not a household manual. In England, Wales and Scotland, the Gas Safe Register says to get fresh air and open all doors and windows, turn off the gas emergency control valve at the meter, unless the meter is in a basement or cellar or the valve is at an LPG bulk tank or storage vessel, put out naked flames and not smoke, not operate electrical switches, and call the National Gas Emergency number, 0800 111 999. For Northern Ireland it gives 0800 002 001. Those numbers are for mains natural gas; for LPG from a bulk tank or a metered supply, it says the number is on the storage vessel or meter, and for gas cylinders it says to check a local telephone directory. It says to see a GP or go to hospital if you feel unwell, and not to turn the gas back on until a Gas Safe registered engineer has checked it. Both the US and UK guidance tell you to get away from the smell and into fresh air.

Carbon monoxide (CO)

Carbon monoxide has no colour and no smell. The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion as the common symptoms, and says people who are sleeping or drunk can die before they have any. It says to put battery-operated or battery back-up CO detectors near every sleeping area, and to replace a detector following the maker’s instructions or every 5 years. The US Consumer Product Safety Commission (CPSC) says: “If you suspect CO poisoning, get outside to fresh air immediately, and then call 911.”

In the UK, the NHS says: “If you think you might have carbon monoxide poisoning: stop using appliances you think might be making carbon monoxide (such as a boiler, cooker or heater) if you can; go outside; get medical advice as soon as possible – do not go back into the affected building until you have got advice.” That page is written for England. It says to call NHS 111 if you think you might have symptoms, and to “Call 999 or go to A&E” if you think you or someone else has been exposed and are finding it hard to breathe, have suddenly become confused, have lost consciousness, are feeling weak, or have chest or muscle pain. It adds: “Do not drive to A&E.” It gives the National Gas Helpline, 0800 111 999, for a gas appliance you think is leaking carbon monoxide (Gas Safe gives 0800 002 001 for Northern Ireland). The tip Keep the gas oven for cooking and the vents open has more on alarms and vents.

Leave gas, burner, electrical and refrigerant work to a qualified person

The Gas Safe Register says all gas businesses and their engineers must be on its register to carry out gas work legally in the UK, and its website has a search to find or check one. In the US, the CDC says to have your heating system, water heater and any other gas, oil or coal burning appliances serviced by a qualified technician every year, and the CPSC urges a yearly professional inspection of all fuel-burning heating systems, including flues and chimneys. ENERGY STAR puts gas and oil connections, gas pressure, burner combustion, the heat exchanger, electrical connections and the refrigerant level on the contractor’s list. It says a dirty burner or a cracked heat exchanger can make equipment run less safely, and that faulty electrical connections can cause unsafe operation. One person warns that a part inside the unit called a capacitor can still hold a charge after the power is cut. Some of the advice online also covers swapping a capacitor or cleaning a flame sensor yourself. This page does not teach either.

What you can do yourself

ENERGY STAR’s maintenance checklist has one set of jobs for you. It says: “Inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump. Your contractor can show you how to do this.” It adds that a dirty filter can increase energy costs and damage your equipment, leading to early failure.

Some people suggest changing filters every two to three months. One person corrects that: cheap fiberglass filters need changing every month, the longer gap is for better-quality filters, and people with pets should check more often. ENERGY STAR’s line is a monthly look, so look monthly and change the filter when it is dirty. The equipment’s manual gives the filter type and size.

One person says central systems usually have the filter behind a latched grille in a wall or ceiling return vent, and that if it is not there the location depends on the house. Some people say the indoor unit itself can be in an attic, a closet or a basement. If you cannot find the filter, ask your contractor to show you; ENERGY STAR says they can show you how to inspect, clean or change it. One person says that in a building with many apartments or flats the filters are often at a central plant and the building looks after them, so ask building maintenance before you assume they are yours.

The outdoor unit

Some people rinse leaves and dirt off the outdoor unit with a hose, and say it helps the unit run. Some people warn that high-pressure water bends the fins. ENERGY STAR lists cleaning the coils as part of the contractor’s visit. If you try it yourself, read the manual for what the maker allows, and switch the power off at the outdoor disconnect or breaker first; the manual or a contractor is the authority here, not this page.

The drain

ENERGY STAR lists checking the condensate drain in a central air conditioner, furnace or heat pump, and says a plugged drain can cause water damage in the house and affect indoor humidity. Some people suggest flushing the drain line monthly, and one person cleans it with vinegar. One person says insects in the drain fittings are a common cause of blockages. One person says a clogged drain line does not make the unit freeze, and that a dirty filter or low refrigerant is more likely.

If the cooling unit ices over

Some people say to switch cooling off but leave the fan running so the air melts the ice. One person says a clogged filter can cause the ice, and another says that if ice returns after the filter is clean, a faulty part or a refrigerant leak may be the cause. ENERGY STAR lists the refrigerant level among the contractor’s checks, so that part is for the contractor.

The thermostat dial

Some people explain that in an ordinary on-off system the dial sets the temperature at which the system stops, so setting it far below what you want does not cool the room faster; it keeps the system running longer. One person corrects the stronger version of that: some systems run in stages or at variable speed, and heat pumps and inverter mini-split units cool or heat faster when the gap is larger. Which kind you have decides it, and your contractor can tell you.

Run it once, early

Many people say to test the system before the weather forces you to: cooling on the first warm days, heating on the first cool days of autumn (fall in the US). Some people say to go earlier, and have cooling checked or switched on in February or March.

Look for these: the system starts and stops, the air comes out cold when cooling and warm when heating, water is not pooling anywhere, and nothing smells of gas. If anything smells of gas, use the numbers at the top of this page. One person says a musty smell from the vents means mould and not only dust; the tip The mould comes back until the damp goes covers what to do about mould. One person uses a digital thermometer at a vent and says the air should be about 20°F (about 11°C) cooler than the room when cooling works, and that less may point to low refrigerant. That is one person’s rough check, not an official test, and a technician decides what it means.

One person says cooling should be run only when the outdoor temperature is above about 55°F (13°C), and that a cooling unit should not be run in cold weather to test it. The maker’s manual gives the real limit for your unit. That is one reason the cooling test fits spring.

Book the check-up early

ENERGY STAR says: “Contractors get busy once summer and winter come, so it’s best to check the cooling system in the spring and the heating system in the fall.” Some people say the same. One person says companies quote higher prices when they are flooded with emergency calls.

ENERGY STAR’s checklist lists what a typical check-up includes, so ask the contractor what yours does. This page has no price for a check-up: ask for the cost before you book and for a written quote before any repair.

For a big repair or a replacement, one person suggests a second opinion, and gives examples where a large quote turned out to be a small fix. One person says that fixing a very old, inefficient unit (they give 20 years) can be a poor financial move. Another says a replacement quote may be wrong when only one part has failed. Which is right turns on how old the unit is, any local rebates and how long you will stay. People also differ on whether to leave a key or door code for a technician when you are out: one says it gets you seen sooner, and another says never to let anyone in unattended. That is your call, and it depends on whom you trust.

If you cannot afford the check-up or the repair

In the US, the LIHEAP page says the program provides federally funded assistance with “home energy bills, energy crises, weatherization, and minor energy-related home repairs”, and that funds can help with “repairing or replacing heating equipment.” What a state offers varies, so ask your state’s program what it covers where you live: the National Energy Assistance Referral line is 1-866-674-6327, and 211 can also point you to local help. The page warns that a message offering you a LIHEAP grant, or asking you for a fee, is one to report to the US Department of Health and Human Services fraud hotline listed on its page. This page does not cover UK help with heating costs; Citizens Advice (England, Wales and Scotland) and Advice NI (Northern Ireland) can say what is available where you live.

If you rent

In the US, who must keep heating and cooling working depends on your state, city and lease. LawHelp.org lists legal aid by state, and 211 can point to local help. In England, GOV.UK’s guide for private tenants says a landlord must make sure gas equipment they supply is safely installed and maintained by a Gas Safe registered engineer, have a registered engineer do an annual gas safety check on each appliance and flue, and give you a copy of the check record before you move in or within 28 days of the check. This page did not check the rules in Wales, Scotland or Northern Ireland. If you are unsure what your landlord owes you, Shelter England, Shelter Cymru (Wales), Shelter Scotland and Housing Rights (Northern Ireland) give housing advice, and Citizens Advice covers England, Wales and Scotland.

If you are in danger now from gas, carbon monoxide, or extreme heat or cold, call 911 in the US or 999 in the UK.