The Physics of Heat Loss
Fall is here. The days are getting shorter and you'll be digging out that winter clothing soon. But before you turn up your thermostat to accommodate the colder weather outside, learn a little bit about how the heating in your house actually works, and how heat loss can occur. Sometimes the only result of cranking up the thermostat is to crank up your electric bill, if your home is experiencing extreme heat loss. So find out how heat travels through your home and what you can do to keep it where you want it.
A law of physics is that energy always flows from warmer to colder areas. This is called conduction. For example, when you sit down on a chair, heat flows from your body into the chair.
Then if you stand up and touch the chair cushion a few minutes later, it will feel warm. This happens because of molecular movement. When you sat down on that chair, your body heat caused the molecules in the chair to start moving faster. Once they started moving, they hit other molecules nearby until all of the molecules near the top of the seat were moving and transferring heat throughout the entire object.
Heat conduction only works through direct contact of solid objects. An example of this in your home would be in your flooring. If your floors are warm or heated, they will help warm up any furniture, carpets, or other objects touching the floors, which will in turn stabilize the heated temperature you've set for your rooms.
When we conduct heat to air or water, it is called convection. This is how we heat our homes. Our heat sources (furnace, boiler, etc.) conduct heat into the air, which then moves away from the heat source towards cooler areas in the room. This phenomenon is called a convection current.
If your room is sealed properly, the convection current will work in your favor to heat up your room quickly and cozily. If you have air leakage to the outside, convective heat loss will occur as your warm air seeks to flow out toward the cold air. This may occur through air leaks around windows, doors, floors, ceilings, and walls.
The third form of heat transfer is radiation, whereby a hot object emits infrared radiation at the speed of light. The radiation is absorbed by anything nearby which is cooler than the hot object. This absorption causes temperature to rise, without heating the air in between the hot and cold objects.
You can feel heat radiation when you hold your hand near your stovetop burner or electric heater. In your house, heat radiation is often lost through the wall immediately behind a radiator if that wall is not insulated.
DIY Fixes for the Main Forms of Home Heat Loss
If your home is not properly maintained to keep heat indoors, your heaters will have to work much harder and longer to keep you warm. This will result in a waste of energy and money. So, if you want to do something that's good for your wallet and the environment, check your home for ways to reduce heat loss.
- Start by looking for air leakage near your windows, doors, floors, walls, and ceilings. If you can feel or see drafts coming in around things like:
- plumbing vents
- electrical outlets
- window frames
- door frames
- recessed lighting
apply caulk or weather stripping to seal the leak.
- Be sure to close the chimney damper so it won’t act like an open window, sucking air up and out through the chimney. You could lose up to 30% of your heat through an open damper.
- If you have an unheated attic accessed through a folding staircase, check the opening's edges for warm air leaking into the (cold) attic from the (toasty) house. An easy test is to switch on the attic light, close the door from below, and look for specks of light around the opening. Visible light means there is space for warm air to escape. Cover these spaces with weatherstripping to keep heat where it belongs.
- Consider adding extra insulation to keep even more heat inside. Start with wall hangings, thick curtains, and rugs. Apply double glazing to your windows and if you want to take on a bigger project, add better insulation to your walls and attic. But be sure to check for air leaks before taking on any costly projects. A little carpet, caulk, and weatherstripping go a long way toward keeping you warmer and energy bills lower.
For installation and maintenance of energy-efficient heating and cooling equipment, contact an expert HVAC contractor.