Why is my upstairs so hot in summer?

Most hot upstairs rooms come down to heat entering from the attic or sun-facing windows faster than the air conditioner can deliver cool air to that floor. Check the attic insulation, the ducts that run through the attic, the eave vents and the windows before you assume the system is too small. Several of those checks take an hour and cost nothing.

Start by measuring the problem

Put a thermometer in the hottest upstairs room and one downstairs, and compare them in the late afternoon and again at bedtime. A room that is hot only in the afternoon points to the roof and the sun. A room that never cools off even at night points more toward ducts or airflow. Write down which rooms are worst, because the pattern is the clue.

The usual causes, in the order to check

Thin or uneven attic insulation. Look across the attic from the hatch. If the insulation is level with or below your floor joists, you should add more.^[1] Look at the eaves too: sometimes there is enough insulation in the middle of the attic and very little along the eaves.^[2] For how to add it, see how to add insulation to an attic. For what the code asks of new work, see what Virginia's energy code requires.

Leaky ducts in the attic. If your air handler or ducts sit in the attic, the cool air is travelling through the hottest space in the house. In a typical house, about 20 to 30 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.^[4] ENERGY STAR lists these signs of poor duct performance: you have rooms that are difficult to heat and cool, and your ducts are located in an attic, crawlspace, or the garage.^[4] Leaks on the return side matter too. Leaking return ducts suck hot/cold unconditioned air into the conditioned space.^[5]

Blocked or poorly vented eaves. A combination of continuous ridge vent along the peak of the roof and continuous soffit vents at the eaves provides the most effective ventilation.^[6] Insulation pushed against the soffit vents blocks the intake side. Do not rush to add a powered attic fan. Electrically powered roof ventilators are not recommended because they consume more energy than they save.^[6]

Sun through the windows. Single-pane windows (windows with only one layer of glass) typically do not have coatings to block solar heat in the summer, increasing air conditioning costs.^[7] Shades closed before the afternoon sun hits do more than shades closed after the room is already hot.

Air and equipment. A closed register, a dirty filter or a blocked return grille starves the upstairs of air. A system that runs constantly and still cannot catch up deserves a service visit; see how much AC repair costs in Virginia.

What you can do yourself

Work in the cool of the morning, because an attic in July can be dangerously hot. Stay on the joists, wear a dust mask and gloves, and stop if you feel dizzy.

Clear anything stuffed against the soffit vents by hand. Check that upstairs registers are open and replace a clogged filter. If you can see a flexible duct that has been kinked, crushed or pulled off its connection, reseat it and seal the joint with mastic sealant or metal tape. Never use duct tape, as it is not long-lasting.^[4]

Inside, the ENERGY STAR advice is simple. In the summer, use the ceiling fan in the counterclockwise direction.^[8] Ceiling fans cool people, not rooms. Switch them off when nobody is there.^[8]

Stop and call a pro if

• The insulation is wet or the framing is stained. ENERGY STAR lists this as a reason to hire a professional first: Wet or damp insulation, indicating a leaky roof.^[3]
• The attic has little or no ventilation, or exhaust vents end in the attic. ENERGY STAR lists both for professional correction before insulating: Little or no attic ventilation, and Kitchen, bathroom or clothes dryer vents that exhaust moist air directly into the attic space instead of outdoors.^[3]
• The ducts are badly damaged, buried, or you cannot reach them. A duct or HVAC contractor can test and seal them.
• The air conditioner runs but the air from the registers is warm. That is an equipment or refrigerant problem for a licensed HVAC contractor, not a home fix.
• You find vermiculite or old knob and tube wiring. Leave them alone and see how to add insulation to an attic.

Getting help in Virginia

If the fixes above are not enough, an energy-minded insulation contractor or HVAC company can find out whether the problem is insulation, ducts or the system itself. More guides are in home repair answers, and you can browse local help at insulation repair providers on Loclis.

When you want a crew to look at the attic, describe your hot room and local contractors will quote it.