Why Is My Upstairs So Hot? How Room Sensors Help

The short answer

Your upstairs runs hot because warm air collects high in the house, the roof soaks up summer sun right above your bedrooms, and the ducts feeding the second floor often run through a hot attic where leaks waste cooled air (DOE Energy Saver Guide). A single thermostat downstairs makes it worse: it shuts the system off once the first floor feels fine. Remote room sensors, such as the ecobee SmartSensor and the Nest Temperature Sensor, let the thermostat steer by the rooms you actually use. Sealing ducts, adding insulation and shading windows fix the causes underneath.

Why one room runs hot or cold

Google's own help page puts it plainly: most homes run at different temperatures from room to room because of windows, room size and sunlight, and a thermostat measures only the room it sits in (Google Nest sensor). The usual causes:

• Warm air rises. Heated air drifts up toward ceilings and upper floors. The Department of Energy even suggests running a ceiling fan clockwise in winter to push that warm air back down (DOE Energy Saver Guide).
• The roof and attic. Standard roofs can reach 150°F (66°C) or more in summer sun (DOE Energy Saver Guide). The rooms right under that roof feel it first.
• Sun-facing windows. Rooms with lots of glass heat up quickly when the sun shines and lose heat faster in winter (Google Nest sensor).
• Leaky or undersized ducts. The DOE says poorly sized, sealed or insulated ducts drive up energy bills, and ducts that leak into an attic or crawl space can add hundreds of dollars a year to heating and cooling costs (DOE Energy Saver Guide).
• Thin insulation and air leaks. ENERGY STAR lists rooms that run too hot or too cold as a sign of inadequate air sealing or insulation (ENERGY STAR heating and cooling guide).
• A thermostat in the wrong spot. ENERGY STAR advises mounting it on an interior wall, away from registers, appliances, lamps, doorways, fireplaces, skylights, windows, direct sun and drafts (ENERGY STAR heating and cooling guide).

Why is my house so cold in some rooms?

The same causes work in reverse. Cold rooms often trace back to leaky ducts, thin insulation, big windows or a thermostat that reads warmer than the rest of the house. ENERGY STAR ties stuffy or uncomfortable rooms to leaky or poorly insulated ductwork (ENERGY STAR heating and cooling guide). The DOE adds that blocked registers, stuck dampers, disconnected ducts or grilles that aim air poorly can all cause discomfort, and fixing them often helps (DOE Energy Saver Guide). Check that furniture and rugs leave your registers clear before you call anyone.

How the ecobee SmartSensor works

The ecobee SmartSensor reads two things: temperature and occupancy (ecobee SmartSensor). You place it in a room, and the thermostat folds that room's reading into its decisions.

• Sensor participation. Your ecobee runs on Comfort Settings such as Home, Away and Sleep. For each one, you choose which sensors count, and the thermostat averages their readings. You can even leave out the thermostat's own built-in sensor (ecobee sensor participation). Want the bedrooms to rule at night? Make only the bedroom sensors participate in Sleep.
• Smooth changes. When a sensor joins or leaves the average, ecobee phases it in or out over 30 minutes (ecobee sensor participation).
• Follow Me. With Follow Me on, the sensors detect which rooms are in use and the thermostat adjusts for comfort in those rooms (ecobee SmartSensor).

How the Nest Temperature Sensor works

The Nest Temperature Sensor measures temperature only (Google Nest sensor). It skips humidity and motion, and you decide which room matters when.

• Pick the sensor the thermostat follows. While a sensor is active, the thermostat uses its reading and ignores its own built-in sensor (Google Nest sensor).
• Schedule by time of day. You can tell the thermostat to follow the living room sensor in the evening and the bedroom sensor overnight. The 3rd gen Learning Thermostat and Thermostat E use 4 fixed time blocks; the 4th gen Learning Thermostat lets you choose 1-hour increments (Google Nest sensor).
• One sensor or an average. The Thermostat E and 3rd gen use one sensor at a time. The 4th gen can average several sensors you select (Google Nest sensor).
• A fallback. If a sensor stops reporting for more than 10 minutes, the thermostat switches back to its built-in sensor (Google Nest sensor).

Nest temperature sensor vs ecobee smart sensor

| | ecobee SmartSensor | Nest Temperature Sensor | |---|---|---| | Senses | Temperature and occupancy | Temperature only | | How many | Up to 32 sensors per account | Up to 6 per thermostat, 18 per home (Google's feature table lists 4 for the Thermostat E and 3rd gen) | | Battery | CR2477, up to 5 years | CR2 lithium, up to 2 years | | Range | Up to 60 ft (18 m) from the thermostat | About 50 ft (15 m), less through walls | | Works with | ecobee Smart Thermostat Premium, Enhanced, Essential and Lite, SmartThermostat with voice control, ecobee4, ecobee3 lite, ecobee3 | Nest Learning Thermostat (3rd and 4th gen), Nest Thermostat E |

Sources: ecobee SmartSensor; Google Nest sensor.

One limit applies to both brands. On a single-zone system, the whole house heats or cools together (Google Nest sensor). A sensor changes which room the thermostat aims for, so a cooler upstairs can mean a chillier downstairs. Sensors balance the trade-off; they can't run two temperatures at once.

Other fixes for uneven temperatures

• Seal and insulate ducts. The DOE calls insulating and sealing ducts in unconditioned spaces "usually very cost effective," and recommends a qualified professional test the work for combustion safety and airflow (DOE Energy Saver Guide).
• Close vents with caution. A Lawrence Berkeley National Laboratory study found that closing registers raised duct pressure and leakage, which often cancelled the savings. It recommended closing the registers farthest from the air handler first and warned that closing more than 60% can restrict airflow enough to trip a furnace's high-limit switch or freeze a cooling coil (Walker 2003).
• Check the dampers and registers. The DOE lists stuck dampers, blocked registers and grilles that aim air poorly as fixable sources of discomfort (DOE Energy Saver Guide). A technician can rebalance airflow between floors.
• Use fans. A ceiling fan lets you set the thermostat about 4°F (about 2°C) higher with no loss in comfort; turn it off when you leave the room (DOE Energy Saver Guide).
• Block the sun. Keep window coverings closed on summer days (DOE Energy Saver Guide). More ideas live in how to cool a room without AC.
• Zoning. Homes with multiple zones can run a programmable thermostat for each zone (ENERGY STAR heating and cooling guide).
• Ductless mini-splits. These heat pumps install without ducts and can heat and cool individual rooms or additions (DOE Energy Saver Guide).

Once the rooms behave, pick sensible setpoints with the best thermostat settings guide. Just Right can set an Apple Home thermostat for the day's weather and time of day. For the bigger picture of why the perfect temperature changes, start at the home page.

When to call an HVAC pro

Call a contractor when:

• One floor stays several degrees off no matter what you try.
• Your system short-cycles. ENERGY STAR notes that an oversized system turns on and off too often and leaves the house uncomfortable (ENERGY STAR heating and cooling guide).
• You suspect duct leaks in the attic or crawl space, or you want ducts resealed or replaced.
• You're weighing zoning, a mini-split or a new system. Ask for a proper sizing calculation (DOE Energy Saver Guide).

The bottom line

• Upstairs heat comes from rising warm air, roof and attic heat, sunny windows and leaky ducts.
• Fix a poorly placed thermostat first, and clear blocked registers.
• An ecobee SmartSensor reads temperature and occupancy and averages the rooms you choose. A Nest Temperature Sensor reads temperature and lets you pick which room the thermostat follows by time of day.
• Close vents sparingly, seal ducts, add fans and shade, and call a pro when one floor stays too hot or too cold.