Why are some rooms hotter or colder than others?

20 12 2012

Having some rooms hotter or colder than others is a problem that can be found in almost every home.  There are many factors that could be the potential culprit, but the two most common are differing thermal criteria and/or improper system design.

Differing thermal criteria refers to actual construction qualities of a room.  In other words, the surface area of external walls, ceilings, and floors and the insulation values in each.  The size and type of windows and which way the windows face in relation to the sun.  Basically, it is any attribute of a room that can be a source of potential heat loss during winter or heat gain during summer.  If you have a room that has a significantly different thermal criteria than the rest of the house, then that room will need heating and cooling at different times than the rest of the house because it is gaining or losing heat at a different rate.  For instance, bonus rooms over a garage have a different thermal criteria because they have unconditioned space under them.  A sunroom will gain heat quicker during summer because of the amount of windows.  Now, if the thermostat for your system is located within the main body of the house and not in that room, then it will not know that the room needs heating or cooling because where it is located doesn’t need it.  This leads to uncomfortable temperatures in the room in question.  Solutions to fix these types of temperature issues range from installing zoning on your existing heating or cooling system or installing a new, typically much smaller, heating or cooling system just for that room (most common smaller system is a mini-split aka ductless heat pump).

Improper system design also leads to uncomfortable rooms.  This means that your heating or cooling system was not installed correctly to take care of the room.  Improper system design can range from under or oversized systems to the most common which is improperly sized or designed ductwork.  The best way to determine if it is a design aspect is to have a design consultant do a manual-j load calculation on your home (Brady Flanary does not charge for this service).  A design consultant can note the thermal criteria of every room and determine how much air flow every room needs and what size system is the best fit for your home.  Then compare that information to the actual design of what you have now.

So, if you have a problem room, take a look around.  If the culprit isn’t obvious, then give the experts a call.  Just know that there are always solutions to any heating or air conditioning problem.