from Dave in Milwaukee, WI:
#664
My home heats up just fine, but does not seem to hold its temperature for a long period of time before the furnace runs again.
It can be influenced by the size/shape/height of your home.
All homes lose heat during cold weather. The greater the temperature difference is between the inside of your home and outside, the greater and faster the heat loss (the closer you set your thermostat to the outdoor temperature, the less heat is lost). In other words, the greatest driving force for heat loss is temperature difference.
Heat loss is also influenced by the size, shape, and height of your home, where it is located (urban, wooded, windy, etc.), and how well it is air-sealed and insulated. Other contributing factors are the number of windows, their orientation to the sun, the type of windows (fixed glass or moveable sashes), the overall efficiency of the windows (single pane, double pane, low-e coatings, storms), and the shading of the windows (trees, nearby buildings, etc.). The number (and size) of exterior doors is another variable. The number and size of “active” chimneys can also influence heat loss as they allow conditioned air to be drafted up their vertical shafts and vented to the exterior. That conditioned air is replaced by cold air that is reheated by your heating system.
Heating systems (furnaces, boilers, space heaters, heat pumps) produce heat to replace the heat that is lost. Their operation is usually controlled by a single thermostat (larger homes may have multiple thermostats to control multiple zones). Some people set their thermostat(s) at one temperature and leave it for the entire heating season, while other people adjust their thermostat(s) depending on their activities or occupancy on a daily basis. Others use programmable thermostats to raise/lower the temperature on a schedule, but can override it at any time.
Heating systems are manufactured in a variety of sizes to allow heating contractors to select one to roughly match the “predicted” heat loss of a home. These predictions are based on load calculations determined by the factors listed above. It is quite common for contractors to oversize heating systems accommodate extreme conditions on those rare occasions when temperatures fall below what is considered normal for a particular region/location. Oversizing can contribute to what is known as short cycling. The too large system produces excess heat for a short period of time and causes the thermostat to be satisfied prematurely. This can cause uneven heating, creating comfort issues, and reduce overall system efficiency.
Published Tuesday, January 19, 2010