Heating Your Home: How Heat Spreads

September 17, 2014
niki dube

There Are 3 Types of Heat: Radiation, Conduction and Convection

Heat transfers in and out of your home three different ways. An effective insulation solution addresses each of these heat types and how it spreads. The principles of heat are best understand through these three characteristics. Understanding them will enable you to develop a home insulation solution for maximum results, both financial and comfort.

What Is Radiation?

Heat TransferRadiation is the primary source of heat generated by the sun. As the materials in your home (e.g., walls, floor, ceiling, etc.) absorb the sun’s radiant energy, this creates conductive heat. Surrounding materials further absorb the conductive heat through convection when surrounding air carries the conductive heat to other objects.

This is the hot air in the room that makes all things too warm. This is called convection.

Radiant foil is your home’s first defense against the hot rays of the summer sun. Up to 97% of radiant heat is reflected back out with high quality radiant foil as a barrier. Generally applied to attics, foil can also be applied to walls. As a secondary benefit, radiant foil, if double sided, will reflect your home’s conductive heat back into the home during winter.  It is the same principle as wrapping your BBQ chicken in aluminum foil after taking if off the grill.

When installing radiant foil, it is critical to allow at least a three inch pocket of air against the outside layer, between the foil and the insulation. Otherwise, the foil will instead create conductive heat with the objects it rests against. To function properly, radiant foil needs air to breath and reflect.

What Is Conduction?

Conduction is the transfer of heat from one object to another (like from hot coffee to the mug to your hands). Insulation prevents conduction. It’s a barrier to outside hot or cold temperatures.

Air is a poor conductor of temperatures. By introducing a protective barrier to outside temperatures, you prevent conduction of cold or hot air in your home.

Insulation comes in many different types of materials: fiberglass, stone wool, denim, and cellulose. Each possesses different R values, which is simply the measure of resistance to heat. The higher R value, the great resistance.

Recommended insulation levelsSource

For instance, if you are insulating an attic, you will want to know the right R value to achieve. By using the Department of Energy map below, you can see that for zone 4, Washington, DC, R30 (about 11” inches of blown in insulation) to R60 (about 20” of blown in insulation) is recommended. For the walls, the amount of cavity space, 4 or 6 inches, will limit the highest R value achievable.

The Energy Star chart above shows recommended R values for homes by region.

What Is Convection?

Convection is the flow of air that transfers and spreads heat or cold. Since air is a poor medium for conduction or holding heat or cold, circulation is good and healthy for homes in general and attics in particular. While buttoning up your attic to prevent air leaks sounds like a good idea, it is important to maintain air flow to move moist, warm air out during summer.

Attics need to cycle air up and out. Generally the flow begins at the soffit and exits through a vent or attic fan. Baffle vents enable this cycle of air in and out. Without the venting, your attic would heat up, encourage mold and force the insulation to work too hard.

The excessive heat also places extra demand on our HVAC system including the cold or hot air flowing through the ducts. Excess heat can also limit the life of your roof shingles.

Understanding the principles of heat and various modes should give you a better understanding of how to effectively manage the temperature controlled air within your home and reduce your energy bill.

Want to live more comfortably and save money? Contact Max for a free consultation and estimate. Call or email today — Max@maxinsulation.us or (202) 750-2180. Ask for Max.