Three Ways Heat Moves

If You’re Not Careful Your Money Will Go With It

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With the temperature on the thermometer hovering near the 100-degree mark over the last few weeks, I’ve been thinking about the need for keeping the outside temperature out and the inside temperature in. This is more relevant if you live in a home that is 40 years old or older. A home built before the mid-seventies it more likely to be effected by the outside temperatures. Not enough insulation, single pane windows and air infiltration are all issues that may need some attention.

 

Understanding how heat moves in and out of your home can help you determine what projects to consider and which ones should be first. A basic misunderstanding is that heat flows upward. Although hot air rises because it is less dense than cool air, heat is unaffected by gravity and flows in all directions. For example, if you apply a heat source to the center of a metal block, the bottom will get just as hot as the top and sides. This heat spreads in all directions and at the same rate. When the air in an attic or fireplace gets hot it rises the air begins to rise. This creates a draft or natural up flow. This is why vented ridges on roofs work so well.

 

Heat moves through your home in three different ways. Each of them needs to be considered and each will require different methods or products to minimize this heat transfer.

 

  • First is conduction, which would apply to the metal block example above or the handle of a cast iron skillet on your stove. This is how most of the heat moves through the walls, ceiling and floors in your home. The temperature difference on either side of a wall determines how fast and which direction the heat will flow through it. The higher the R-value of insulation in that wall the slower the heat transfer.
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  • Convection transfer is similar to conduction, but occurs in fluids and gases. When it is windy outside, cold air increases the loss of heat from the wall more than if the air was still. This is the “wind chill” factor you hear weather forecasters talk about. Convection ovens use this form of heat transfer to cook by moving hot air. This is why they cook faster than conventional ovens.
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  • The last type of heat transfer is radiation, which is probably the most difficult to understand. Radiation does not need a transfer material to move heat. This is how the sun warms the earth though millions of miles of empty space or how the top of a steak gets seared in the broiler. Radiant heat transfer is generally more of an issue in the summer, but shouldn’t be ignored during the winter. Radiant heat is not blocked by standard insulation, but rather by reflectivity. An example of this would be the way dark colors of roofing, siding, etc. absorb heat and light colors reflect it.For example, if your home has a particularly cold wall on the northwest, there is likely both conductive and convective heat loss to blame. Adequate wall insulation and high quality windows and doors in the wall would be the best place to begin. Also wind breaks, i.e. evergreen trees or privacy fences, can help. There are several small ways to make improvements, including new weather stripping, filling voids in foundations with spray foam, sealing around electrical and plumbing openings, etc.NOW would be a good time to give some consideration to these issues. Investing in these kinds of home improvements can help keep you warmer in the winter, cooler in the summer, as well as provide an economic payback with lower utility bills. Do what you can to keep the money in your home and minimize transferring it with the heat.
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