In a poorly insulated house, start by limiting unwanted heat gain and cooling the occupied space safely. Adding more fans or opening every window is not automatically the right answer. Outdoor temperature, humidity, air quality, sunshine and the home’s construction all affect what will help.
Keep people safe first
Do not rely on home-cooling tips when indoor conditions are unsafe or a person is becoming unwell. Use an adequately cooled location and follow local heat alerts. Children, older adults and people with health conditions may need extra help. Fans and bowls of ice are not substitutes for effective cooling during dangerous heat.
Reduce sunlight before it becomes indoor heat
Use suitable window shades or curtains when direct sunshine is entering. Record which rooms and windows become uncomfortable first rather than buying the same treatment for every opening. Exterior shading can be useful where the building and fixing method allow it; do not install awnings or coverings without checking wind, access and structural requirements.
Keep window treatments clear of heaters and required ventilation. A blackout fabric’s appearance alone does not establish its thermal performance or suitability for a particular window.
Ventilate when outdoor conditions help
Open windows for cooling only when outdoor conditions make that useful and security, weather and air quality permit it. Bringing hot or humid outside air into an air-conditioned room can increase the load. Preserve required background and combustion ventilation; do not seal or block it in an attempt to keep the room cool.
The US Department of Energy’s home-cooling guidance treats ventilation, shading and mechanical cooling as different strategies. There is no single window schedule that suits every climate and building.
Use fans for personal comfort, not a promised room-temperature drop
A fan moves air; it does not actively remove heat from a closed room like refrigerant AC. Direct airflow where it helps an occupied space, follow the fan’s instructions, and keep equipment dry and stable. Do not put ice or water where it can spill into electrical equipment. A dehumidifier also releases heat into the room, so it is not a direct replacement for AC.
Reduce avoidable indoor heat
Switch off unnecessary lights and unused heat-producing equipment where doing so is safe. Compare the actual equipment rather than assuming fluorescent lamps are always cooler than modern LEDs. Avoid unnecessary oven use during the hottest period if another safe food-preparation option is available.
Keep AC intakes and outlets unobstructed and follow owner-serviceable filter instructions. Do not repeatedly lower the setpoint to compensate for a fault, ignore a hot plug or use an extension arrangement the manufacturer prohibits. For selecting equipment, see our window AC size and fit worksheet.
Record the pattern before paying for building work
Note room, time, sunshine, wind, indoor/outdoor conditions and which cooling equipment was operating. A room that heats in afternoon sun presents a different initial clue from a room that feels drafty only in windy weather. Neither observation alone measures insulation performance.
Our air leaks versus poor insulation guide includes a room-by-room observation sheet and explains when professional assessment is more useful than another appliance purchase. DOE’s air-sealing guide also distinguishes air barriers from insulation and stresses safety when planning improvements.
Make the improvement order specific to the home
Use the record to discuss solar control, ventilation, moisture, cooling capacity and the building envelope with an appropriate professional. Do not diagnose hidden insulation by touch alone, disturb unknown old materials, or assume a fixed percentage saving. An assessment can identify which work addresses the cause rather than repeatedly treating the symptom.
Editorial review: October 12, 2026. TemperatureMaster Editorial revised this guide using the primary sources linked below, with AI-assisted research and writing. This is a research-based owner guide, not a report of hands-on testing or an individual technician diagnosis. See our editorial policy.
