Issues of using a sealed building cavity as duct instead of traditional ductwork

[DavidJ]

I didn't know Energy Gauge did calcs,so inquiring with our estimators ,they said it shows btus,but says on the screen they are btus per "X" sq ,feet,always higher then the Man. J calc.

I'm having a hard time interpreting this. Are you saying that your folks say that Energy Gauge shows a need for more BTUs or less BTUs than Man. J for the same structure? Did they indicate how far they find it to be off?

[adrianf]

paul

single story or 2 story

percentage of glass to living area

[dash]

I'm having a hard time interpreting this. Are you saying that your folks say that Energy Gauge shows a need for more BTUs or less BTUs than Man. J for the same structure? Did they indicate how far they find it to be off?

Sorry ,the energy gauge btus is always higher then the Manual J load calc.

[paul42]

paul

single story or 2 story

percentage of glass to living area

Difficult to describe - The house is built on a slope and is one story over an above ground walk out basement.

Living space has 10 foot ceilings & 175 sq. ft. of windows, 2,230 sq. ft. There are three small west facing windows that get some sun starting about 6pm. All of the other windows are completly shaded during the summer months.

The basement has a stepped floor, 6 to 10 ft ceilings, approximately 1,800 sq.ft. of useable storage space, and no windows. The baement is above ground, so three of the walls are frame construction. The fourth wall (east) is a steep dirt bank with a vapor barrier.

[DavidJ]

Sorry ,the energy gauge btus is always higher then the Manual J load calc.

That is interesting. When working with Calcs Plus we found that they calculated that the building needed a higher tonnage that what Energy Gauge said that the building needed. And I am quite confident, since I did it myself, that all the variables were keyed correctly into Energy Gauge.

There are several versions of Energy Gauge out there as seen at http://www.energygauge.com/. Do you know what version you guys are using? I don't know that they all calculate loads the same.

[paul42]

Yes, walls are not our area of greatest concern in Central Florida. However, once you've dealt with everything else, then they start constituting a larger piece of the total pie.

2,000 square feet per ton! Very impressive, especially reading your later post about all the company you had this weekend. So what's in your secret sauce to achieve that besides R-49 , or has that already been discussed on another thread on this site?

The secret sauce is
1. put the air handler and duct work in conditioned space
2. shade ALL the windows in the summer
3. control infiltration.

We laid out the house so that almost all of the windows are on the North or South side, and with a three foot overhang and large porches, they get no sun during the summer months. There are three small windows on the west end tucked up under the eaves that start to get a little sun around 6pm, and I paid extra for very low e glass in those.

Another approach to making the ceiling drywall airtight is to spend 2 or 3 hours in the attic with a foam gun before they blow in the cellulose. Get a gun with a longer nozzle, a decent headlamp, and the work goes fairly quick.

My wife and I love our new house - we set our thermostat at whatever is the most comfortable for us and our cooling bills are still a fraction of what our friends and neighbors are paying.