Heating hot water in a home is about 15% of your utility bill.
Cooling your house in the summer can account for half of your utility bill and heating is about 36% of it.
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Where Does the Air Come From?
The Energy code requires all these openings to be caulked, have a gasket or be sealed.
The Sizing is Always too Little
Studies done by the Department of Energy have shown that return air systems (ducts/chases) are undersized the majority of the time.
Manual D states "The return air system MUST establish a low resistance return air path between every room and the return side of the blower cabinet. If these paths are not established, the air flow through some or all of the supply air outlets will be affected."
Part of the static pressure in every duct system is created by the return air system.
The effects of inadequate return air paths are as follows:
Duct leakage on the return side can case the structure to have an excessive positive pressure, this however is accomplished by drawing hot/cold air from outside the envelope and will lead to many problems not the least of which is loss of capacity. This will have a serious effect on the system's ability to control humidity within the structure.
Ventilation Air is Necessary to Accomplish
Adding controlled ventilation in hot-humid climates seems to be a contradiction. However, supplying outside air increased the latent load. The key is to provide the amount of air that is needed and not 1 CFM more. Next address the resulting latent load.
The problem, however, can be a little more difficult if the effect of duct leakage is considered. The truth is that most structures suffer from EXCESSIVE air changes as a result of duct leakage when the air handle operates as a result of supply duct leakage. The key is to stop the uncontrolled ventilation by sealing all ducts properly then add controlled ventilation. This approach will typically lower the latent load.
Recent studies have shown that duct leakage can cause an induced air change of 150 to 200 CFM or more. In stark contrast controlled ventilation of approximately 60 CFM would reduce the infiltration load to 90 to 140 CFM resulting in a lower latent load.
Remember that it is only necessary to provide enough outside air to place the structure in a slight positive pressure with respect to the outside. Research shows a 1 to 2 Pascal positive pressure with respect to the outside is sufficient.
The proper approach to ventilation in a hot-humid climate is to size and install the system correctly. This will help in minimizing the need for outside air.
A quality installation should be achieved if ALL of the following are accomplished:
The necessity for completing heat gain/loss calculations and completion of an accurate duct design cannot be overemphasized. In the end, this is the only method to ensure that the system to be installed will function in concert with the structure.
Once this has been accomplished, then the need for a professional installation of all the components that are required for a complete HVAC system within a given structure cannot be stated strongly enough. Anything less can lead to complications that depending on the structure may not be able to be corrected at a cost that the structure owner could manage.
Any one of the following or some combination thereof could cause the cooling/heating system to be incapable of maintaining temperature set-point and or maintaining control of humidity levels within the structure.