What is a “cool” room?

A “cool” room is a room or area of a house that feels cooler than the surrounding rooms or areas. Sometimes this is one room, such as a bonus room over a garage. It can be a basement or perhaps it is just one area within a room which is noticeably cooler.

A cool room occurs when there is more heat lost from the room than is being supplied to it. There are two sides to the issue; heat loss and heat supply.

Our perception of temperature

Humans can detect a temperature difference as little as half of a degree. Our perception of being warm or being cool is also affected by age, level of activity, air movement and health. The perception of warm and cool is also affected by the humidity level. A hot humid room seems warmer than a hot dry room. A damp, cool room feels cooler than a dry cool room. A still environment feels warmer than one with air movement. Flooring products also make a difference (i.e. a tiled floor feels cooler than a carpeted floor.)

Matching expectations with construction reality

The concept behind maintaining a constant temperature is simple: supply enough heat to compensate for the heat lost. This is easier said than done when each area of a house loses heat at a different rate and often only one heating unit and control is used to supply heat.

The influence of the outdoor environment

All exterior climate conditions influence heat loss in a home.

Wind can affect heat loss in a house. The exposure of a room to the wind varies from one part of a house to the next. Some rooms are sheltered by neighbouring buildings, decks or trees while others are exposed to the sometimes-prevailing winds. Cold air mixed with wind produces a wind causing exposed walls to cool more quickly than sheltered walls. The effect can be more pronounced if the room is on a second story, over a walk-out basement or facing a lake or open field.

Barriers to the outdoor environment

In our homes the walls, floors, ceilings, windows and doors are all used as barriers to separate the outdoor environment from the indoor environment. These barriers do not stop the transfer of heat, they only slow it down. Controlling heat loss and gain is balanced with creating a strong envelope that buffers climactic effects while allowing natural light in.

Some materials used in constructing walls transfer heat more quickly than others. For example, wood members used for framing conduct more heat through the wall than the cavities between the wood studs that are filled with insulation. Additional wood is needed in some areas of walls to support windows or to tie wall corners together. These variations in materials results in slightly uneven temperatures from one wall to the next and across the surface of the wall.

Windows do not resist heat flow nearly as well as walls do. Windows can be said to be “thermal holes”. The insulation value of the windows is roughly 10% of the adjoining walls. When sun shines on windows, heat moves through the window into the house. If there is no sun shining on the window, heat flows from the house to the outdoors. Some rooms have very few windows while some rooms have large banks of windows, which can result in cold areas in a room.

Typical construction practice

Sometimes construction methods can be upgraded to minimize wall temperature differences, but these must be discussed with your builder before construction. Although missing insulation can contribute to a cool area, this is seldom the major cause of a cool room.

Required heating design parameters

Heating contractors must calculate the overall heat loss of a home in order to recommend the size of furnace that is capable of maintaining an indoor air temperature of 22°C in all living spaces and 18°C in unfurnished basements at the outside winter design temperatures. The winter design temperature varies slightly from one location in the province to the other but is based on the very cold days of the year. In order to deliver even heat to all areas of the house, the system must be balanced to provide sufficient flow to all rooms especially those with higher heat loss.

The heat delivery system

Supplying even heat in a home can be a challenge when one furnace is used. Some rooms are closer to the furnace and some are further away. As heated air moves along the ductwork, some heat is lost as it transfers through the duct and some is lost as air leaks out of unsealed joints in the ductwork. The ducting may detour around an obstruction such as a stairway to a bonus room or a beam supporting floor joists. The increase number of bends in the ducting results in more heat loss and reduced air flow.

To create even heat, the air used to transport the heat must circulate. If it does not, the effect is similar to blowing into a straw when one end is blocked. Debris, toys or a dirty furnace filter can also reduce air movement and restrict the heat supply. The path of air flow between heat supply duct and the cold-air return duct should also be open.


Usually there is one thermostat controlling heat to the whole house. The thermostat may be located in a room with less heat loss than the cool room, or in a hallway where nobody spends any significant time. In these situations, the heating system supplies heat to satisfy the room where the thermostat is located, which may not be enough for the cool room. The heat flow to each room can be increased or decreased by adjusting air flow rates to individual rooms at the room outlets or registers.

Improving heat to a cool room

Before a heating contractor is called in to check the performance of the heating system there are steps that you as a homeowner can take to correct a cold room situation.

Issues and potential solutions:

  • Adjust heat flow (floor registers) to decrease the airflow to the warm room and direct more air to the cold room
  • Ensure heat ducts are free of debris
  • Clean or replace the furnace filter, per your manufacturers recommended service intervals
  • Ensure heat ducts are not obstructed by furniture
  • Adjust heat flow (floor registers) to decrease the airflow to the warm room and direct more air to the cold room
  • Reduce the low temperature set time of a programmable thermostat
  • Run the furnace fan continually to circulate more air into and out of the cool area
  • Reduce the effect of a heat source, such as a fireplace, in the room with the thermostat
  • Add a supplemental heat source with its own thermostat to the cool room
  • Ensure the cold air return is not blocked
  • Undercut the door or leave the door to the room open to allow air circulation from the supply outlet and for heat to enter the room
  • Use a less dense floor covering product (i.e. carpet), or add a rug to the floor
  • Adjust registers in the home so more air is delivered into that room or install a dedicated duct fan.
  • Install or close existing curtains when the area is occupied, to add an extra insulation blanket (note, this can increase condensation on windows)
  • Add a space heater or electric heating appliance to offset the temperature
  • Ensure air from the heat source is not deflected away from the glass
  • Ensure the ducting is clear of debris and the furnace filter is clean
  • Increase heat flow to the window area by opening the register under the window and closing registers in other areas
  • Check the condition and seal of the window often, and replace worn or old weatherstripping to reduce air leakage
  • Install or close existing curtains when the area is occupied, to add an extra insulation blanket to the windows (note this can increase condensation on the window)

Still experiencing a cool room after trying the above suggestions? A heating contractor can confirm the sizing of the furnace in relation to the heat loss of the house.

They can calculate the amount of heat that the delivery system is capable of sending to the cool area and calculate whether the delivery capacity is sufficient for the calculated heat loss.

The content provided in this blog is for general information purposes only and nothing contained herein should be taken or relied upon as legal advice. Although every effort is made to ensure the accuracy of information shared on this blog, the information may inadvertently contain inaccuracies.