Knee wall attic space contains HVAC & ducts. Should I re-insulate, power ventilate or both?
jsgift
| Posted in Energy, Heating & Insulation on
Our finished 3rd floor is insulated as shown in the figure below, with the knee wall insulated as shown on the left side of the figure. We live in NC. Though some tall trees provide decent morning and late afternoon shade, the attic space gets pretty hot in the summer. Our 3rd floor HVAC and ducts are in the knee wall and above the collar beams, respectively, and 2nd floor ducts are in the knee wall. It has been that way for over a decade without incident, but our electric bill is above average. To reduce our electric bill and increase the life expectancy of our HVAC system, which of the following options would you recommend?
1. Re-insulate so the knee walls are insulated as on the right side of the figure below.
2. Add insulation insulation to the knee walls as shown on the right side of the figure, keeping the knee wall and floor insulation that is already there.
3. Do nothing to the insulation.
Options 4, 5 and 6 would be doing any of the above while adding an appropriately sized and properly mounted gable fan to (presumably) pull air up the ridge wall and out the gable vent.
Replies
HVAC in unconditioned attics is pet peeve.
How is that something which is so obviously a bad idea standard practice? I'd insulate the roof as on the right side of your drawing and bring the HVAC into the thermal envelope.
Power venting
Also, I would not power vent the attic. That's almost always a bad idea as well. Usually, the soffit vents can't provide enough make-up air, so the fan depressurizes the attic and sucks the remaining make-up air from the conditioned space, actually increasing your cooling load. Take a look at greenbuildingadvisor.com for some good discussions on this topic.