I’m sure everyone has noticed when climbing a ladder during the winter to change a light bulb the air is much warmer at the top of the room than it is as the bottom. Hot air rises, otherwise we wouldn’t enjoy a balloon race at the summer picnic. Indoor air quality is affected by air movement (both hot and cold), by heat and by moisture intrusion.
There is a direct connection between heat loss and heat gain as it relates to your home’s protective skin, also known as the building envelope. Ideally your home should maximize heat retention during the winter and minimize heat gain during the summer. The best energy efficient design should incorporate a well sealed and insulated wall structure that helps protect you from temperature change and block unwanted moisture and air from entering your home. These mechanisms are known as transmission and air leakage.
Thermal resistance (your home’s wall insulation# and surface area are two factors that govern the rate of heat transmission. Air leakage is measured in CFM #cubic feet per minute# and depends on the surface area of the holes in your home and the pressure differences between the outside and inside. A large difference in temperature, known as ∆T #Delta “T”#, creates a greater pressure. Maintaining a balanced interior pressure will improve indoor air quality. Sealing or reducing the number of air leaks in your home not only stops unwanted air infiltration #both cold or warm air# but also lowers the amount of moisture that rides along the air flow path and helps maintain pressure balance.
A second source of pressure change occurs when air leaks in through the building skin as a result of your home’s air conditioner. Air leakage into your home is often 2-3 times greater when the air handler #your air conditioners’ fan motor# is operating. The unit “de-pressurizes” your home and increases the opportunity for air infiltration. Stopping the holes will lower the pressure difference.
A third, and often overlooked, pressure change can occur as a result of leaky ducts in either the supply or the return air chamber of your heating system. This type of unbalanced system can also create a depressurized “combustion appliance zone” #CAZ#. An example would be a back drafting chimney #and its accompanying odor# or a flame roll-out of the water heater. Both have been known to cause house fires. Also, if you’ve noticed that as you shut a bedroom door the last few inches the door is “sucked shut”, you should have a balance test performed on your heating system. These “out of balance” pressure zones can create unhealthy conditions by pulling unwanted air from a water heater exhaust #can create dangerous level of carbon monoxide# or an increased level of soil gases #radon).
Maintain your home by regularly checking for and repairing air leaks to your heating system and your home’s skin. Doing so will keep you family healthy and lower your energy bills at the same time.
