Attic Space Vs Plemum Space

Don t use the foamed attic space as a conditioned plenum.

Attic space vs plemum space.

Plenum trusses create a reverse bulkhead in the center of the attic space where ducting can be housed in an insulated area. Compare that with the daily 140 degree temperatures found in vented attics. This by definition is a plenum air space and requires plenum rated cable. That space typically has about a 10 12 degree difference than the conditioned space below it.

I wonder if the nec definition of the word plenum would actually apply to the entire attic space. The plenum truss bulkhead adds only the amount of inside conditioned space required to house the ductwork by modifying the roof framing to create a boxed in area in the otherwise unconditioned attic. Cabling between the many devices and to the users runs through this open floor space. So when we have a choice we prefer hvac systems located under the house.

A plenum space is a part of a building that can facilitate air circulation for heating and air conditioning systems by providing pathways for either heated conditioned or return airflows usually at greater than atmospheric pressure. The energy savings touted by unvented attics can be as high as 20. It s easy to see your point about eliminating ductwork from the attic. A two room addition on the 1st floor has limited attic space and a 4 crawl space.

Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum. A basement is below and an attic is above the main part of the house. It will increase your load and contaminate your house air if it has been converted from a ventilated attic to a sealed attic. This allows intensive cooling to be pumped through the space under the floor to cool the servers switches routers etc.

Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. Rarely will a sealed foam insulated attic deviate more than 15 degrees from the living space temperatures below it. Think about the volume of space normally associated with return air ducts vs the volume of space involved in an attic space. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.

However i have two questions if i want to centrally air condition my entire house.