Where Is the Best Place to Put a Thermostat?

A thermostat does not know how warm your house is. It knows how warm the air is at one spot on one wall, and it runs the furnace, boiler or heat pump until that spot is satisfied. Put it somewhere that tracks the rooms you live in, and the house is comfortable. Put it in a draft, a sunbeam or the path of a supply register, and you get a comfortable thermostat and an uncomfortable house. Location is one of the first things we look at on a thermostat service or replacement call, because no amount of programming fixes a thermostat that is reading the wrong air.

Why does thermostat location matter so much?

Thermostat location matters because the thermostat treats its own reading as the temperature of the entire house. If the spot runs warmer than the living space, the thermostat shuts the heat off early and the rooms stay cool. If it runs colder, the heat keeps going and the rest of the house overshoots. Either way the setpoint on the display stops meaning anything, and people start chasing comfort by turning the dial, which makes the pattern worse.

A misplaced thermostat also changes how the equipment runs. A thermostat that gets a blast of warm air a moment after the burners light will cut the call short, over and over, which is the classic setup for short cycling. One sitting on a cold wall will keep a heat call going long after the house is warm.

What makes a good thermostat location?

A good thermostat location is an interior wall in a central, regularly used room, where the air is typical of the house and nothing warms or cools that spot on its own. In most homes that means a living room or a main hallway wall that backs onto other heated rooms. Mounting height should follow the thermostat manufacturer's installation instructions. The checklist:

• An interior wall with heated space on both sides, not a wall to the outdoors or an unheated garage.
• A room people are in most of the day, near the middle of the house or the main living floor.
• Free air movement around it, not tucked behind a door, a bookcase or a curtain.
• Out of direct sunlight at every time of day, including low winter sun through a south window.
• Well away from supply registers, return grilles that pull air across it, and exterior doors.
• Away from heat sources: the kitchen range, lamps, televisions, a fireplace or a wood stove.

Which spots throw a thermostat off?

Bad thermostat locations and what they do to the rest of the house

Location	What the thermostat sees	What the house feels
Exterior wall in an older house	A cold wall surface and cold air in the cavity	Rooms run too warm
Above or across from a supply register	Warm air soon after each start	Short cycles, rooms run cool
Near an entry door	Cold blasts every time the door opens	Heat runs long, house overshoots
Kitchen or beside a lamp or TV	Heat from cooking or electronics	Rest of the house runs cool
Sunny wall	Solar warming during the day	Rooms cool off on bright days
Bottom or top of an open stairwell	Warm air rising past it	Upstairs and downstairs drift further apart
Near a wood stove	Radiant heat from the stove	Central heat stays off while far rooms chill

Why is an exterior wall a bad spot in an old Duluth-area house?

An exterior wall is a bad thermostat location in an older, lightly insulated house because the wall itself is cold, and the thermostat reads that cold as a cold house. Plenty of homes on the hillsides here were built with little or no insulation in the walls, and in a heating season with roughly 9,000–10,000 heating degree days, an outside wall spends months noticeably colder than the room air beside it. The thermostat keeps calling for heat to warm its own corner, and the rooms in the middle of the house get too warm.

The same thing happens out in older farmhouses around Willow River and Toivola, where the original thermostat often went on whatever wall was closest to the furnace wiring. In houses heated with propane or electric plus a wood stove, as many are around Wright, a thermostat within sight of the stove has a second problem: the stove's radiant heat satisfies it while bedrooms on the far side of the house get no central heat at all.

Can a stairwell or open staircase throw off a thermostat?

Yes. A thermostat at the bottom of an open stairwell in a tall house sits in the path of warm air rising to the upper floors, and that moving warm air shuts the heat off before the main floor is comfortable. Tall, narrow hillside houses with open staircases are the worst case. Heat rises up the stairwell, the upstairs overheats, the thermostat downstairs is flattered by the warm draft passing it, and the split between floors gets worse the harder the system works.

A thermostat at the top of the stairs does the opposite: it sits in the warmest air in the house and keeps the lower floors cold. When an upstairs-downstairs split is the complaint, the thermostat location is worth checking before anyone talks about bigger equipment, and balancing the duct system through ductwork and airflow work often helps as much as moving the control.

Can drafts behind the thermostat fool it?

Drafts coming through the wall behind a thermostat can fool it, because the hole drilled for the thermostat wire often opens into a wall cavity connected to the basement, the attic or an outside wall. Cold air travels up the cavity, comes out through the wire hole and flows across the thermostat's sensor from behind. The thermostat reads cold air the room never feels. Sealing the wire hole behind the thermostat base stops it, and it is something we check and do whenever a thermostat is off the wall for service or replacement.

What if moving the thermostat is not practical?

When moving a thermostat is not practical, a remote temperature sensor or zoning can fix the same problem. Many modern thermostats accept one or more wireless room sensors and can control to a single room or an average of several, so the thermostat can stay on its old wall while the reading comes from where people actually live. Zoning goes further, splitting the duct system into areas with their own thermostats and dampers, which suits tall houses with a persistent floor-to-floor split.

Actually moving a thermostat means running new low-voltage wire from the equipment to the new location, patching the old hole and sealing both wire penetrations. In a finished older house, finding a clean wire path is the real work. It is also a good moment to add a common wire, which a smart thermostat needs to run reliably, and to confirm the new display reads normally; our guide to what thermostat messages mean covers the ones you will see.

Signs your thermostat is in the wrong place

The signs of a badly located thermostat are rooms that sit colder or warmer than the setpoint, a thermostat that disagrees with a separate thermometer, and heat that starts and stops in short bursts. Short cycling can also come from an oversized furnace, a clogged filter or a failing part, so our guide to why a furnace short cycles is the place to rule those out. Sun-dependent comfort, a room that is fine on cloudy days and cold on sunny ones, points straight at location.

If the thermostat needs to move, needs a remote sensor, or the whole control needs replacing, that is our kind of job; it involves wiring back to the equipment and should be done with the power off at the furnace. Start with a look at thermostat relocation, sensors and smart controls, and let us pick the wall.