home heating & cooling systems
(continuation)

ducts

The delivery system is often an overlooked element in a home's heating, ventilation & air-conditioning (HVAC) installation. Regardless of the efficiency ratings of heating & cooling systems, they all rely on properly designed, installed & insulated ducts to deliver the heated & cooled air.

Proper duct sealing & insulation affect a house's comfort & energy use significantly. Poorly designed ducts & poor duct work can cause uneven air distribution, poor house ventilation & problems w/ humidity levels. The resulting conditions are areas that are too cold or too hot, an increase in dust & other contaminants being circulated & growth of mold & mildew.

sealing materials

Routinely, instances have been found where sections of ducts were never installed, connected, or had broken or fallen away completely, leaving gaps in the system.

Using duct tape to seal duct joints & seams has been prohibited in a number of building codes because it will peel & crack when exposed to humidity & temperature changes.

The term "mastic" is commonly used to describe a number of sealing systems, including some types of adhesive tapes. Mastic is a gooey paste recommended for sealing duct gaps & seams.

insulation

In a typical home, many supply & return ducts are routed through unconditioned spaces such as the attic, basement/crawl space, or garage. Because of the temperature extremes in these spaces, even a perfectly sealed duct system will lose energy across the duct surface. Studies have found that uninsulated ducts can lose about the same amount of energy through conduction as they do through leaks.

To reduce this energy loss, route ducts through conditioned spaces where possible & insulate them well in unconditioned spaces. You can insulate by simply wrapping insulation (usually fiberglass insulating sheets) around installed, secured & sealed duct systems, or by using flexible, pre-insulated ducts. Sealed & insulated metal ducts tend to perform better & last much longer than flexible insulated ducts. Poorly suspended ducts, especially flexible ducts, can sag over time, restricting airflow through the system. Also, the corrugated inner surface of flexible ducts resists airflow.

duct testing methods

It is a good idea to test a home to make sure it has an adequate duct network & that sealing methods are working as they should. A typical forced-air distribution system's duct network delivers conditioned air from the furnace, heat pump, or air-conditioner to the registers in the living spaces & air from these areas back to the appliance to be heated or cooled.

Several organizations have developed testing methods to determine residential duct tightness & several utilities have started test programs. Homeowners should not test & repair ducts themselves, but hire qualified experts.

heating systems

heat pumps

A heat pump can save as much as 30 to 40 percent of the electricity you use for heating. Gas heat pumps as well as electric heat pumps are available for home use.

Heat pumps are rated for heating & cooling in terms of capacity & efficiency. Capacity ratings are generally in British thermal units per hour. Heating efficiency for air source heat pumps is indicated by the Heating Season Performance Factor (HSPF). Heat pump efficiency depends on outdoor temperature. The performance of an air source heat pump in heating mode decreases w/ the drop in outside temperature.

During the cooling period the heat pump operates as a central air conditioner. The Seasonal Energy Efficiency Rating (SEER) tells you the seasonal cooling performance.

Federal efficiency standards require conventional heat pumps to have an HSPF rating of at least 6.8 & a SEER rating of at least 10.0. The most efficient air source heat pumps have an HSPF rating between 7.7 & 10.0.

heat pump energy saving tips when buying & using