There’s nothing worse than a home that won’t cool down in the summer. Many homeowners struggle with hot houses even when their air conditioning (AC) is running full blast. The causes can range from simple problems, such as clogged air filters, to more complex issues, such as refrigerant leaks or improperly sized AC units.
The good news is that you can diagnose and even fix many of these issues without professional help. This article will explore why a home might stay hot and provide practical solutions to help homeowners beat the heat and save on energy costs.
1. Leaking Ductwork
One of the most common reasons for a hot home is leaking ductwork. When the ducts that distribute cool air throughout the house have gaps or holes, precious cooled air escapes before it reaches its destination. This makes the home feel warmer and wastes energy.
How To Identify Leaking Ductwork
Duct leaks often occur where lines branch off or separate. Turn on the furnace fan and see if you can feel air escaping from these areas. Use a smoke pencil or incense stick to locate tiny leaks by watching where the smoke wafts away unnaturally.
DIY Duct Repair
Here’s how to fix leaking ductwork for those who are comfortable tackling it themselves:
- Turn off the fan.
- Apply metallic foil tape over the hole or gap.
- Apply duct mastic over the tape and joints to improve the seal.
Watch How to Repair Leaks in HVAC Ductwork to learn more.
2. Clogged Air Filters
A clogged air filter is another common cause of a hot home. Regularly changing your HVAC air filter is crucial for efficient cooling and indoor air quality.
Why Air Filters Matter
All the air in your home passes through the AC return grill and filter before reaching the air handler. A dirty air filter restricts airflow, causing the air handler to work much harder. This increases your cooling bill and can lead to expensive repairs if the air handler breaks down. Clean air filters also help reduce allergens and improve air quality.
How To Change an Air Filter
To change your air filter, locate the filter housing (usually near the air return vent) and remove the old filter. Note what size filter you need. Once you have the new filter, insert it into the space facing the correct direction. Close the filter housing.
We recommend changing your air filters every 1–3 months, depending on factors such as pets, allergy sensitivities, and general air quality in your area.
Watch How to Change the Air Filter in Your Home to learn more.
3. Leaking Windows
Windows can be a significant source of heat gain in a home. If you feel radiant heat even when the blinds are closed and curtains are drawn, your windows might be leaking.
Single-Pane Window Issues
Single-pane windows often develop leaks when their glazing putty fails. To fix this:
- Remove old glazing with a putty knife or paint scraper.
- Apply new window glazing around the frame.
- Smooth the glazing compound with a putty knife.
- Once set, paint over the glazing with exterior house paint.
Solar Heat Gain
Even intact windows can transmit solar heat. To reduce this:
- Add window film that can reflect up to 72% of the sun’s heat.
- Install thermal curtains or cellular shades that provide additional insulation.
- Consider upgrading to double-pane or low-E windows for better insulation.
4. Attic Heat Infiltration
Summer heat can seep through the roof into the attic, causing your AC to work overtime. These strategies can help limit heat transfer from the roof to your living spaces below:
Install an Attic Vent Fan
An attic exhaust fan near the roof’s peak can help keep the attic cooler, lower energy bills, and extend the roof’s lifespan. Proper attic ventilation also helps your home’s AC keep the overall indoor temperature comfortable.
Add More Insulation
Proper insulation reduces heat gain. When choosing insulation, consider its R-value, which measures its resistance to heat transfer. Higher R-values mean better insulation. Blown-in insulation or rolls of batt insulation can improve a home’s thermal resistance, especially in older homes with inadequate attic insulation.
5. Heat Infiltration Through Walls
Solar heat can quickly warm up exterior walls and transfer that heat inside, especially in brick homes. Proper wall insulation is key to preventing this issue.
Choosing the Right Insulation
The right insulation depends on factors such as climate, wall thickness, and budget. Fiberglass batts for standard two-by-four walls provide an R-11 to R-15 insulation value. Spray foam insulation offers a higher R-value (R-14 to R-28, depending on the product) and provides an air seal that fiberglass cannot.
Always install insulation carefully or hire a professional for the job so there are no gaps or thermal bridges that could compromise effectiveness.
Additional Measures
Consider using radiant barriers or reflective foil insulation in areas where wall insulation alone isn’t sufficient. These materials reflect radiant heat away from your home and can be especially effective in warmer climates.
6. Refrigerant Leaks
A refrigerant leak stops your AC from cooling your home effectively. Leaks can develop over time and are often hard to detect without professional equipment. Signs of a leak include:
- Warm air coming from vents
- Hissing sounds from the AC unit
- Unexplained spikes in energy bills
If you suspect a leak, call an EPA-certified HVAC technician. These professionals can locate and repair the leak and then recharge the system with the correct amount of refrigerant.
Importance of Professional Help
Handling refrigerant without proper training and equipment is dangerous and often illegal. Only certified professionals trained in safety and environmental regulations should work with AC refrigerant. Regular maintenance checks can help identify leaks early and mitigate long-term damage.
7. Clogged Evaporator Coils
AC evaporator coils absorb heat from indoor air and expel it outside. Dust and debris can clog these coils and reduce efficiency, causing your system to overheat or even shut down.
DIY Coil Cleaning
You can clean minor coil clogs yourself. Follow these steps:
- Turn off the AC unit.
- Clean the coils with a soft brush, vacuum, or compressed air.
- For stubborn dirt, use a commercial coil cleaner.
We recommend calling an HVAC professional for heavily soiled clogs or if you’re unsure about handling the task. Cleaning your evaporator coils once a year helps maintain optimal system performance and prolong the unit’s lifespan.
8. Blocked Ductwork
Blocked ductwork can prevent cool air from circulating properly, leading to uneven cooling and hot spots in your home. Common causes include debris accumulation, pest damage, or improper installation.
Professional Duct Cleaning
You can sometimes locate and remove blockages yourself, but you’ll often need to hire an HVAC cleaning company. These professionals have specialized tools to scope and clean ductwork. Regular professional cleaning can also improve indoor air quality and system efficiency.
Preventative Measures
Install high-quality air filters and schedule regular maintenance to help prevent blockages. Seal ductwork joints with mastic sealant to prevent air leaks and reduce the risk of blockages from dust and debris gathering at loose joints.
9. Aging or Inefficient AC Unit
AC components wear out and become less efficient over time, leading to reduced cooling performance and higher energy bills. It might be time to replace your AC unit if it’s 15–20 years old or older.
Benefits of Upgrading
Newer, high-efficiency AC models can provide better cooling performance, improved comfort, and significant energy savings.
Regular maintenance and tune-ups can help improve your unit’s efficiency until you’re ready to replace it. A qualified HVAC technician can catch small issues before they become big problems, extending the unit’s life. We recommend scheduling service annually.
Selecting a New Unit
Consider the Seasonal Energy Efficiency Ratio (SEER) rating when selecting a new AC unit. Higher SEER ratings indicate more efficient units, which can lead to substantial energy savings over the unit’s lifetime. Consult an HVAC professional to make sure you get the right-sized unit for your home.
10. Improperly Sized AC Unit
An AC unit that’s too small or too large for a home can lead to ineffective cooling. An undersized unit will struggle to cool the space, while an oversized one will cycle on and off frequently, causing temperature fluctuations and increased energy use.
Hire an HVAC technician to perform a Manual J load calculation. This determines the correct AC size for your home based on factors such as square footage, insulation levels, and local climate. An appropriately sized unit will help cool your home effectively without high energy bills.
Proper installation is just as important as selecting the right size. Even the best unit will perform poorly if not installed correctly.
FAQ About Why Your Home Is Hot
How can I tell if my air conditioner is not working efficiently?
Turn on your AC unit by lowering the set point on your thermostat. Then, hold your hand over a duct register. You should feel cold air moving somewhat fast. If it doesn’t feel cold or you don’t feel any airflow, you have an AC system issue. Another sign your AC unit is inefficient your thermostat never getting to the temperature you set.
When should I call an HVAC professional to help with my home's cooling issues?
You should call an HVAC company after ruling out common issues you can fix yourself. Check the thermostat, replace the air filter, and verify the breaker for your AC unit is on. You can troubleshoot things further, but you’ll likely need an HVAC technician to help you fix it anyway.
What are the most common reasons for uneven cooling in a home?
The most common reason for uneven cooling in a home is sun exposure. In the U.S., south-facing rooms get much more sun. This heats them more than the north side of the house. Other common culprits include an oversized AC unit and poor ductwork design.
