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4 Answers

How much AC tonnage do I need for a 6,700-sq.-ft. house?

I am building a 6700 sqft house in Brownsville, Texas. The house is not the usual wood frame but is being built from Areated Autoclaved Concrete also called Hebel Blocks. This is a very efficient insulating material. The inside walls are 6" thick and the perimeter walls 8. The ceiling heights vary from 10' to 18'. The living room has 6 windows that at 9'x6' and 2 windows 9'x2.5'. The rafters will received 6" open cell spray foam.

In General questions | Asked By Omar Jalil | Jun 6 12
21 Answers

Vapor-open exterior sheathing

In building up a list of vapor open exterior sheathings to recommend for cold climates (with the goal of creating walls that can dry to the outside and can accomplish the recommended 5:1 outside to inside perm ratio), I've found myself a bit stumped by how to measure the permeance of traditional diagonal 1x white pine sheathing.

In Green products and materials | Asked By Jesse Thompson | Jul 30 10
0 Answers

HRV/ERV and placement of intake


I was contemplating adding mechanical ventilation to my home in the Boston area. I've got a couple of questions I was hoping all you experts could help me with:

1) HRV Vs. ERV: Reading through the posts on HRV/ERV, I am still confused as to what would be the appropriate choice for my geographic location (Boston, MA). Some say HRV and others point to an ERV. We don't have an issue with moisture on the windows in the winter and during the summer the house "feels" humid for only short periods. Any thoughts on a choice here?

In General questions | Asked By Allan Wood | Jun 6 12
7 Answers

Wall assembly review?

Hello, again, GBAers.

I'm in the planning stages of a ~1850 sq. ft. PassivHaus-compliant home in Salt Lake City (5B) [1]. After reading Martin Holladay's post on the Belgian PassivHaus home rendered uninhabitable [2], I am hoping to get some feedback on my wall assembly design [3].



[1] http://1010-design.blogspot.com/2012/02/more-detail.html
[2] http://www.greenbuildingadvisor.com/blogs/dept/musings/belgian-passivhau...
[3] http://1010-design.blogspot.com/2012/06/wall-assembly.html

In Energy efficiency and durability | Asked By Jan Nielsen | Jun 5 12
3 Answers

Does a heat pump always make sense?

We thought to replace a 10 SEER AC unit and a 45-year-old oil furnace with a heat pump. When we look at the potential savings to purchase a 3T unit, it doesn't add up. In our 2400 sq ft home, we use 450 gallons of oil/year and $400 (worst case) of electricity for the AC. We would need to add a 20kW heater to the heat pump in order to replace the furnace.

Should we just wait until the furnace or AC break?

In Mechanicals | Asked By Mike Stelts | Jun 4 12
2 Answers

Laars tankles water heater

I was at my in-laws summer house over the weekend and went into the mechanical room. I was surprised by how warm the room was. They have a Laars Mascot tankless condensing boiler for hot water and radiant heat.

There was no water being used and the radiant system was not calling for heat.

Since this is an on demand system, I figured it would not give off much, if any, heat since the house had been vacant for at least a week.

In Mechanicals | Asked By Kevin Karlberg | Jun 5 12
3 Answers

Sun porch for solar gain?

I'm retro fitting a small ranch with 12" cellulose walls, 20" cellulose cold attic, warm crawl space. It has a long screen porch along the south west wall. I am considering enclosing it with folding patio doors so it can generate solar gain during the cold seasons and still open up during the summer. I am in South Jersey.

In addition, I am planning to add mini-splits to heat and cool the space. It currently is electric baseboard ( no gas in the area). The finished house will be 2 stories and about 2200 sq ft.

In Green building techniques | Asked By Michael Arnold | Jun 4 12
2 Answers

Air tightness & testing?

The common method of expressing test results of air tightness tests is air changes per hour. @ 50 pascals. How is the building volume calculated? Does it include exterior wall volume (use outside dimensions)? Does it include an unheated basement? or crawlspace? In testing are vents for ventilation systems (HRV.ERV) capped? Are dryer or range vents capped? What is "state of the art" air tightness? What are best known test results?

In PassivHaus | Asked By Jerry Liebler | Jun 4 12
4 Answers

HELP! apprehensive about adding exterior XPS insulation

Hello everyone, this is my first post as an avid DIY homeowner. I have renovated multiple homes and I am a big fan of adding 2" XPS insulation board to the exterior as part of a window and siding upgrade.

This "NEW" house just sent me a curve ball. I just discovered that my "NEW" 1982 home in upstate New York (zone 6) has 1/2" foil faced polyiso between the studs and exterior sheathing.

In Energy efficiency and durability | Asked By Brandt Minkler | Jun 3 12
5 Answers

Exterior EPS foam fasteners?

Does anyone have a recommendation for fasteners for exterior foam application? I am applying 6-7" of exterior EPS foam in two layers (2x3", overlapping joints). Ideally I am looking for pneumatic nails with washers so that the fastener does not penetrate the foam.


In Green products and materials | Asked By Erik Lobeck | Jun 4 12
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