Should I leave climate control on?

Generally, no: it’s more energy-efficient to use a setback or smart scheduling rather than running climate control constantly. For homes, that means adjusting your thermostat when you’re away or asleep; for cars, avoid leaving the system on unless you’re using it for a specific purpose such as preconditioning before you drive or defogging in chilly weather.

Home climate control: when to keep it on or switch it back

Energy use and safety go hand in hand in residential settings. The goal is to maintain comfort and protect property while minimizing waste. Smart thermostats and weather-based routines can automate these decisions, but your local climate and home insulation also matter.

• Short trips (a few hours): activate a low-energy mode or a modest setback rather than leaving the system at full temperature. This reduces energy use while keeping the home from becoming uncomfortably cold or hot on return.


• One-day absence (8–12 hours): set the thermostat to a modest setback—roughly 60–65°F (15–18°C) in winter and 78–80°F (26–27°C) in summer. If you have pipes at risk of freezing, avoid dropping below about 55–60°F (13–16°C).


• Extended absence (several days): use an extended energy-saving setting appropriate for your climate; many people use a lower heating temperature in winter and a higher cooling temperature in summer, while ensuring unheated spaces don’t fall below freezing in winter and humidity doesn’t rise excessively in summer.


• Special equipment and situations: homes with heat pumps, humid climates, or multi-zone systems may benefit from auto or adaptive modes that balance energy use with dehumidification and comfort needs.

Smart thermostats can handle these adjustments automatically, learning your routines and adjusting to weather patterns. They can also help you avoid costly energy waste when you’re away on vacation or dealing with unusual weather.

Safety and comfort considerations

When temperatures drop, avoid letting unheated spaces fall well below freezing to protect pipes, plumbing, and cold-sensitive electronics. If you have plants or pets at home, tailor the settings to their needs while still pursuing energy savings. Humidity control matters in damp climates, so consider a dehumidifier or timer-based ventilation if mold risk is a concern.

Car climate control: leaving it on when parked

In a parked car, leaving climate control running generally wastes fuel or drains the battery and can incur gear and mechanical wear. The best practice is to turn off climate control unless you’re actively preconditioning the cabin or defogging windows. If you routinely need cabin comfort on arrival, plan ahead with appropriate methods and local regulations in mind.

• Short parking periods (minutes to a few hours): turning the system off is usually fine; you can use defogging briefly if necessary when you return, and manually re-activate heat or AC as needed.


• Longer parking (2+ hours in extreme heat or cold): avoid leaving the system running. If you must precondition, use remote start or preconditioning while the vehicle is plugged in (especially for electric or plug-in hybrids) to minimize battery impact.


• Hybrid and electric vehicles: preconditioning while the vehicle is still plugged in can preserve battery range and reduce the energy draw when you begin driving. Always follow manufacturer recommendations and local safety guidelines.


• Defogging and safety: in cold or humid conditions, you may briefly run the defog function to clear windows before you drive, but turn it off once visibility is restored to minimize energy use.

Many newer cars offer energy-saving modes that optimize climate control for comfort with minimal impact on range or fuel—as long as you use them intentionally rather than leaving climate control on by default.

Additional considerations: pets, plants, and humidity

Pets and indoor plants may require a more stable baseline than the average empty home, particularly in extreme weather. In winter, an extremely low setback can stress animals; in hot climates, avoid excessive heat that could endanger pets or cause plant damage. Humidity control matters in regions with high dew points or mold risk; a dehumidifier or ventilation timer can help maintain a healthier indoor environment without full-time cooling.

Summary

In most situations, leaving climate control on full-time is unnecessary and costly. Use programmable or smart thermostats to create sensible setbacks when you’re away or sleeping, and reserve continuous operation for specific needs like preconditioning, defogging, or protecting vulnerable pipes and ecosystems. For vehicles, avoid running climate control while parked; use remote start or preconditioning when appropriate and safe, especially for electric and plug-in vehicles. With thoughtful scheduling and climate-aware routines, you can stay comfortable while saving energy and reducing emissions.

What is the most economical way to run AC?

The most efficient way to run an AC is by combining smart thermostat use with good home maintenance, like sealing air leaks and keeping vents clear. Use a programmable thermostat to set higher temperatures when you're away and a comfortable, consistent temperature (around $72-75^\circ$F) when you're home. On hot days, close blinds and curtains, and use fans to supplement cooling to reduce strain on the system. 
This video explains how to use your AC more efficiently during hot weather: 56sKGW NewsYouTube · Jul 5, 2024
Thermostat and cooling 

• Use a programmable or smart thermostat: Set a schedule to automatically adjust the temperature, cooling your home before you arrive and raising the temperature when you are away or sleeping. 
• Avoid over-cooling: Do not set your thermostat much lower than $20^\circ$F difference from the outside temperature, as it is inefficient and strains the system. A reasonable setting is around $72-75^\circ$F when you are home. 
• Consider using fans: Ceiling fans can help circulate air, making you feel cooler, so you can raise the thermostat a few degrees without sacrificing comfort. Ensure they are rotating counter-clockwise in the summer. 

Home maintenance and insulation

• Seal air leaks: Inspect windows and doors for drafts and use weather stripping or caulk to seal any gaps. This prevents cool air from escaping and warm air from entering. 
• Improve insulation: Adding insulation to your attic can help keep your home cooler in the summer and reduce the workload on your AC. 
• Keep vents clear: Make sure air vents are not blocked by furniture or clutter, and regularly check for dust and debris that may be partially clogging them. 
• Clean or replace filters: A dirty air filter can decrease airflow and make your system work harder. Change or clean your air filter every 1-3 months, or more frequently if you have pets or allergies. 
• Close curtains and blinds: Keep curtains and blinds closed, especially on sunny windows, to block direct sunlight from heating up your home's interior. 

This video explains how to make your HVAC system more efficient: 1mMonkey Wrench Plumbing, Heating, Air & ElectricYouTube · Sep 12, 2023
Other tips

• Use only when necessary: If you're not home or aren't using a certain part of the house, close the doors and turn the AC down or off in those areas to save energy. 
• Minimize heat-generating activities: Try to do chores like running the dishwasher or laundry during cooler parts of the day or evening. 
• Keep outdoor unit clear: Ensure the outdoor condenser unit is not shaded by plants or debris, which can impact its efficiency. 

Does climate control use more fuel?

If you're comparing a car using climate control to a car that doesn't have the system at all, the climate-control-equipped car will use a fraction more fuel due to the extra energy needed to run the system.

Is it cheaper to run AC all the time or turn it on and off?

Even if you prefer leaving your air conditioner running when you're home, we recommend turning your system off anytime you leave the house for more than an hour or two. This practice can lower your energy bill and save you money in other ways.

What temperature should you leave an unoccupied house at?

For an empty house, keep the heat at 55°F (13∘13 raised to the composed with power13∘C) in winter to prevent pipes from freezing and set the AC to 85°F (29∘29 raised to the composed with power29∘C) in summer to prevent mold growth and damage. The specific temperature can vary, but it is crucial to maintain a consistent, moderate setting to protect the home from extreme temperature damage and high utility costs associated with large temperature swings. 
Winter

• Set the thermostat to 55°F (13∘13 raised to the composed with power13∘C). This is the most critical temperature to protect against frozen pipes and water damage. 
• Consider a slightly higher temperature of 60°F: if you have plumbing on exterior walls or live in a climate with extremely low temperatures. 
• Open cabinet doors: under sinks to allow warm air to circulate around plumbing. 
• Insulate any exposed pipes: with foam sleeves or heat tape. 
• Turn off the main water valve: as an extra precaution, especially if you are leaving for a very long time. 

Summer

• Set the thermostat to 85°F (29∘29 raised to the composed with power29∘C) or higher. This helps prevent mold growth by controlling humidity and protects your belongings from extreme heat. 
• Consider a higher temperature if you have furniture or materials sensitive to humidity, such as wood floors. 
• Use the A/C as needed to maintain a constant temperature rather than making large, energy-intensive adjustments. 

Important considerations for both seasons

• Humidity control: In summer, a high setting on the A/C will also help control humidity. In winter, excessive humidity can damage wood floors or furniture, so consider monitoring and controlling it if necessary. 
• Regular checks: If you are leaving for a long period, have a friend or neighbor check on the house periodically. 
• Internet-connected thermostats: Use a smart or internet-connected thermostat to monitor indoor temperatures and humidity levels remotely. 
• Air filters: Replace your air filter before leaving to ensure proper air circulation.