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5 Answers

Dehumidify only?

In Boston area, 5A region. I own a condo in an old building with average insulation and air sealing and a gas forced-air furnace.

I currently don't have central AC. My furnace needs replacing, and AC is cheaper as a package install. My city has about 400 cooling degree days per year, and my 1000 sqft condo is on the first floor and shaded by other buildings, so the heat is not too bad. Humidity is, however. A whole-house dehumidifier with a DIY install would be cheaper than AC, and we could conceivably take it with us if we moved. It would also handle humid days in the spring and fall.

In Mechanicals | Asked By Stephen Thrasher | Sep 6 12
6 Answers

Is it the average mean, or the average low temperature I should use to calculate BTU needs and condensation points?

So I am calculating whole wall R-values and condensation point within the wall.....
In my calculations so far I have used the average "low temp" of the coldest month. Actually I used a temperature just a bit 1-2 degrees colder than the average low temperature listed. But in further reading, I noted that some only use the average "mean" temperature of the coldest month, and not the average of the "low" temp. Which is it...cause it would "mean" the difference in a few inches of insulation on the exterior?

Zone 6A - 8200 or so Heating degree days

In Energy efficiency and durability | Asked By brad hardie | Sep 10 12
1 Answer

Insulating a crawl space that has partial infloor heating above and drain / water lines below

I'm having a bathroom installed in a sunroom conversion to 4 season room. Due to the layout of the room we were hoping to only install infloor heating to the bathroom portion as it won't get much heat off the rad system that exists on the main floor.

The entire room itself is over a non vented crawl space. I know I can either insulate the walls or the ceiling in the crawlspace. Using rigid xps foam what would be better to ensure moisture isn't built up as well as preventing pipes from not freezing in the winter? I get both hot humid summers and cold winters in Southern Ontario, Canada.

In GBA Pro help | Asked By Mike Tew | Sep 11 12
7 Answers

HELP - Lost thermal break at the slab meeting code

We are building a house in upstate NY on a floating insulated slab using ICF's on top of footers. We presented the attached original plan to the town and the building inspector came back with a requirement that we put 12 inches of concrete under our double wall with no part of the wall bearing on foam (see revised wall section). He was able to cite a section of the code that says a foundation wall must have a minimum width equal to the wall size (with two exceptions that don't apply to us). This is one argument that we will not win.

In GBA Pro help | Asked By Elizabeth Kormos | Sep 10 12
1 Answer

Refinance & Appraisal on Historic Net Zero Home

You've heard this before . . . no comps, no deal.

We're refinancing our 111-year-old net zero energy home. At my request the appraiser used PV Value and included the Appraisal Institute Green Addendum. He valued the home added $40-50k to the home for all the "green" features (including geothermal and 8.1kw solar resulting in net positive energy production over any rolling 12 month period). See GBA case study about home: http://www.greenbuildingadvisor.com/homes/mission-zero-house-net-zero-re....

In General questions | Asked By matthew grocoff | Sep 11 12
4 Answers

New ORNL Roof Design

Stumbled upon this new roof design by ORNL, what do you all think


In Energy efficiency and durability | Asked By Roger Lin | Sep 11 12
5 Answers

Range hood ruins energy remodel!

I installed this Broan hood in our kitchen this summer: http://www.broan.com/products/product/qp230ss30-under-cabinet-range-hood...

It has some nice attributes, mainly a nice, quiet, 100CFM low setting that works perfectly well for most things.

In Energy efficiency and durability | Asked By David Meiland | Sep 9 12
10 Answers

Interior side of exterior sheathing temperature calculation. Does the calculation change when you are calculating for the roof?

In a REMOTE or PERSIST type assembly, does the calculation for determining the temperature at the inside surface of the exterior sheathing differ between walls and roof? Or is the temperature calculation the same? For instance if you used the same exact assembly at the roof as you did on the walls - would the temperature or condensation point be different at the interior side of the sheathing?

Obviously I will be using higher r-values in the roof (R-60)minimum, and (R-40) minimum in the walls.

In Energy efficiency and durability | Asked By brad hardie | Sep 6 12
5 Answers

An excellent video of a blower-door test at a Passivhaus

Check out this excellent video of Skylar Swinford (of Hammer and Hand) describing a recent blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. at their current PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. project, dubbed the Karuna House:


Here's a link to the video on the Hammer and Hand web site. (Since the site is having problems, the YouTube link above is probably more dependable):

In Energy efficiency and durability | Asked By Martin Holladay | Sep 10 12
0 Answers

Insulating interior and exterior of block wall

Hi folks,

I have a block wall foundation in northern Vermont. The exterior (below grade) is faced with 2" rigid insulation all the way to the footing.

The inside of the walls are not insulated at all. And I have plenty of extra foil faced 2" rigid left over from a previous project. So I am thinking of using it to cover the inside walls too, and air seal their joints. I am thinking of fastening to the wall using adhesive only (PL or liquid nails).

Overall, anything else I should consider ahead of time or be aware of?

Thanks, Steve

In General questions | Asked By Steve Mattera | Sep 10 12
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